Electrical equipment,
wiring and batteries
for a boat

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This page updated: June 2012

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Batteries     Battery

Battery ratings:
  • CA: Cranking Amps: current flow the battery can deliver for 30 seconds at 32 F without dropping below 1.2 volts per cell (total of 7.2 volts for a 12-volt battery).
  • MCA: Marine Cranking Amps: same as CA.
  • CCA: Cold Cranking Amps: similar to CA and MCA, but at 0 F.
    Usually CA or MCA equals approx 1.25 times CCA.
  • HCA: Hot Cranking Amps: similar to CA etc, but at 80 F.

  • RC: Reserve Capacity: number of minutes over which the battery can deliver 25 Amps of current at 80 F without falling below 1.75 V per cell (about 88% of capacity, or 10.5 V on a 12 V battery).
  • AH: Amp-Hours: inverse of RC, being instead the amount of charge that a battery can deliver at 80 F over a specified number of hours (usually 20) without dropping below 1.75 V / cell. A battery that can deliver 5 A of current for 20 hours has a 100 AH rating.

  • Weight: in pounds (heavier gives more capacity, in general).

  • Size: Group 24, group 27, group 31, 4D, etc.

Two kinds of batteries:
  • Starting.

    Produces short burst of high power.
    Use to drive engine starter motor.

    From Ample Power:
    The simplest, and least expensive battery is the starting battery. It is constructed with many very thin plates. The combined surface area of the many plates allows high currents to flow through the battery ... great for the purpose of starting engines. The starting battery can't be deeply discharged without a significant risk of destruction. A recent study showed that no starter battery survived more than 18 deep discharge cycles ... most survived no more than 3 deep discharges.

  • Deep-cycle.

    Produces steady flow of power over a relatively long period of time.
    Use to drive appliances, inverter (to produce AC), lights.

    From Ample Power:
    To enable deep discharges, the plates must be made thicker and the insulating separators made from more expensive materials than the paper used in starting batteries. Thicker, but fewer plates means that the battery won't sustain as high a rate of current, but will permit deeper discharges without imminent failure. Golf cart batteries and heavy duty 8D units are thus designed with the purpose of supplying moderate currents for sustained periods. They aren't a true deep-cycle battery, however, and should be charged soon after any extensive discharge.

    By making the plates thicker yet, and using expensive fiberglass matte separators, a battery can be made which provides a great many deep cycles ... 400 or more 100% discharges. This kind of unit is called a traction battery and will cost several times as much as golf cart batteries in the same capacity range. Batteries made by Surrette and Rolls use very thick plates and offer great longevity when low rate discharges are followed by long slow charges.

Several battery technologies:
  • Dry-cell (e.g. AAA, AA, C, D batteries for flashlights and such).
    Often last less than a month at sea in Tropics; alkalines best.
    Recharging small batteries article in 6/2001 issue of Practical Sailor.
    Typical capacities of these batteries: 9V = 625 mAH at 9 V, AAA = 1250 mAH at 1.5 V, D = 20500 mAH at 1.5 V.

  • Wet-cell (aka "flooded"; usually lead/lead-oxide/sulphuric-acid/water).

  • Gel-cell.
    Accept 10% to 15% higher charge rate; can discharge deeper; have significantly lower self-discharge rate; no fluid maintenance; won't leak if rolled.
    But they are more expensive; more finicky about charge voltage; have less AH for the same physical size; live for fewer cycles than a traditional flooded battery; hard to replace when overseas. "Sealed" in that you can't check/add water, but they still have small vents that can emit hydrogen.

  • AGM (Absorbed Glass Mat).
    Charge at same rate as flooded batteries.
    No fluid maintenance; won't leak if rolled.
    More expensive; hard to replace when overseas. "Sealed" in that you can't check/add water, but they still have small vents that can emit hydrogen.

  • TPPL (Thin Plate Pure Lead).
    Very high charge-acceptance rates (CARs), so high that they can burn out alternators or trip breakers on shorepower for battery-chargers.
    Nigel Calder's "Battery revolution" New technology, so price and lifetime are unclear.

  • Wet NiCad (Nickel-Cadmium).
    Can be totally discharged and can accept a 100% recharge rate. But have low recharge efficiency.
    From Beau on the IRBS live-aboard mailing list:
    Be careful of NiCad. They have no series resistance. This means that the entire power of the battery can be dumped into whatever is absorbing the current, like a wrench or screwdriver. A lead-acid battery has enough series resistance to limit the current to a few hundred amps. To see 150 Amp/Hours dumped in a few seconds is a scary sight. Extreme care should be taken to put fuses in any NiCad battery pack to limit the dump rate; you can weld with these.

    Also, NiCad batteries typically have a maximum cycle count of about 200 to 300 cycles.
  • NiMH (Nickel-metal-hydride).
  • Lithium-Ion.
    Very high charge-acceptance rates (CARs), so high that they can burn out alternators or trip breakers on shorepower for battery-chargers.
    Can be discharged down to 20% state of charge (SOC) repeatedly without shortening life.
    Almost no energy losses when discharging and recharging.
    Extremely expensive, partly because every cell must be microprocessor-controlled to avoid over-charging or under-charging relative to other cells (cell-balancing).
    Nigel Calder's "Battery revolution"

  • LiFePO4 (lithium iron phosphate).
    Wikipedia's "Lithium iron phosphate battery" New technology, so price and lifetime are unclear.

Paraphrased from "This Old Boat" by Don Casey:
  • Auto/starting batteries: thin plates, hundreds of amps in a few seconds, immediately recharged, damaged by deep discharge.

  • Deep-cycle batteries: thick plates, deep discharge over period of time before recharge, don't discharge below 50% of capacity.

  • Gel batteries: allow deep discharge and rapid recharge, can be fully discharged but rapid recharge limits life, and max life is less than that of deep-cycle batteries.

Summarized from article by Stephen Sommer in 1/2004 issue of Southwinds magazine:
  • Flooded batteries: require good ventilation, because they vent hydrogen and corrosive vapor, mostly while charging. Cheapest and most forgiving of abuse (overcharging, hot environment), but not forgiving of neglect (check water level often).

  • "Sealed" batteries (gel and AGM) really are not totally sealed; they can emit hydrogen.

  • All batteries, even "sealed" batteries, produce heat while charging, so need some ventilation.

  • AGM's have a higher surge power capability than gel-cells. If using a relatively small bank for engine starting or an inverter with a large surge capability, prefer AGM's.

  • "Sealed" batteries are 2 to 4 times as expensive as flooded batteries.

  • Gel-cells may have longer service life than AGM's.

From Andina Marie Foster on The Live-Aboard List:
> I know it's not the best thing to mix batteries but:
> If you had 2 used AGM batteries, one 75 AH and the other
> 100 AH what would happen if you put them in the same bank?

They will work just fine.
Matching type (AGM) is the most important.
Matching age and history is second important.
Matching capacity is least important.

Someone's paraphrase of Nigel Calder:
If you are not living aboard, and the boat is untended for long periods and deep discharging is inevitable, gel batteries will give better service. If you do live aboard and can provide proper flooded battery maintenance (specifically keeping water levels up, preventing deep discharge, and periodic equalization charging) on a continuous basis, flooded batteries give much higher performance per unit weight / volume and better durability.

From Frank Holden on Cruising World message board:
"Gels dislike overcharging more than most and are probably the easiest to fry in a terminal way."
[Tom Neale agrees.]

From article by Jan S. Irons in Nov 2008 issue of Blue Water Sailing magazine:
"Outside of the USA, gel cells or AGM batteries are difficult to find, so when our gel cells failed to hold a charge, we had to reconfigure our system to wet cells."

From AIM in Marathon FL:
  • Gel batteries retain 100% of the energy pumped into them by a charger; flooded batteries retain only about 80%.

  • Gel batteries self-discharge about 1% per month (Practical Sailor editor says 3% per month at 68 F); flooded batteries self-discharge about 2% per day.

  • Gel battery manufacturers have tested with chargers from Raritan and Sentry; get those chargers. Want a charger with no float voltage at all for gel batteries.

  • The best rating to consider for house batteries is "minutes of discharge at X amps"; you decide which standard value of X (8, 15, 25, etc) makes sense for you.

BoatSafe's "Marine Battery Primer"
David Pascoe's "Solving Chronic Battery Problems"
Bill Darden's "Car and Deep Cycle Battery FAQ"
Ample Power primer
BatteryStuff.com's "Battery Articles"
von Wentzel's "Battery Types: Flooded versus AGM and Gel"
phred Tinseth's "Batteries -- and Other Electric Stuff"
Uve Rick's Battery Page
SailNet - Tom Wood's "Standard Onboard Charging Systems"
BoatU.S.'s "12 Volt Electrical Systems"
SailNet - Tom Wood's "Creating a 12-Volt Spreadsheet"
Ron Romaine's "Offshore Electrical Systems"
SailNet - Kevin Jeffrey's "Battery Bank Design"
SailNet - Kevin Jeffrey's "Choosing Batteries"
West Marine articles
Larry Janke's "Common Battery Myths"
Mo Girard's "Pulse Battery Technology" (about PulseTech)
AGM batteries reviewed in 10/15/2000 issue of Practical Sailor
Deep-cycle battery test in 1/15/2001 issue of Practical Sailor

From Norm on the IRBS live-aboard mailing list, 31 Aug 1999:
My suggestion is to combine all your deep-cycle house batteries into one bank for simplicity.

Reduce voltage differences in the bank by making sure all the wires are the same wire size, all the short jumpers connecting the six volt batteries into twelve volt batteries are the same length, all the longer wires connecting the pairs of six volt batteries into the parallel bank are the same length. The idea being that the voltage drops across all the wires in all the battery pairs will be the same if all the wires are the same.

The battery wires should have ring terminals soldered on to them. You can use copper tubing to make your own terminals ... snip ...

Clean your battery terminals well. I use a knife to scrape, followed by a small wire brush. Apply Vaseline/baking soda mixture (described below in "hints") liberally to all connections when making them up.

If you wish to go even further to insure equal voltages, you can "CrossConnect" the bank, that is - connect together all the points of equal voltage with jumpers. Imagine a drawing of a battery bank of three pair of 6 volt batteries connected series/parallel to form a 12 volt house battery with the positive end of the bank at the top of the page and the negative end of the bank at the bottom of the page and the 6 volt batteries in two horizontal rows with all positive terminals up and all negative terminals down. In addition to all the normal connection wires, make up 12 more jumpers. Use them to connect all the positive terminals of all the upper row of batteries together, then all the negative terminals of those batteries. Then all the positive terminals of the lower row of batteries together and finally all the negative terminals of the lower row of batteries. This way you can insure that equal voltage points are as equal as you can get them.

... snip ...

The best solution might be to mount another, generic, internally regulated alternator on the main engine just to charge the engine starting battery while the big, expensive, alternator/regulator takes care of the house battery. This situation would have the most independence and (except for the mechanical aspects) simplicity. This is the way it is when I am using just my genset and it works very well.

Some hints for flooded batteries:

The hydrometer is the last word in state-of-charge.

Melt a jar of Vaseline in some hot water and stir in some baking soda to make a good battery terminal protectant.

Check batteries every month for specific gravity, water, tightness of terminal fasteners, cleanliness, and security of tie-downs. I discovered a dead cell in a 8D during a monthly hydrometer check and was able to exchange it for a new one while it was still under the 100% part of the warranty (Sam's Club) and I could still start my main engine.

Very carefully pour some baking soda/water solution over the battery tops, wires, and terminals to neutralize the acid that collects there (youraren't they?). Avoid at all costs getting any inside - use plain distilled water if you have any qualms about contaminating the electrolyte.

Do an equalize charge at least once a month - every two weeks is better.

Keep a record book on all the above.
Anonymous comments on the above message:
> ... combine all your deep-cycle house batteries into one bank for simplicity.

Redundancy and flexibility are key to successful cruising. The suggestion above puts all your eggs in one basket, which is a sure invitation to trouble.

> ... Reduce voltage differences in the bank by making sure all the wires are the same wire size, all the wires are the same length. ...

This may be fine in a system designed to operate a cabin in the woods, and is theoretically correct, but (within reason) is unnecessary on a cruising boat.

> The battery wires should have ring terminals soldered on to them. ...

Never solder 12 volt connections on a boat. The marine environment causes solder to corrode like crazy, and vibration causes it to crack. The major marine retailers sell solder in their stores - only for the purpose of soldering RF connections, like those found on the PL-259 connectors on your VHF radio antenna. Those same retailers sell crimp type connectors for use in 12 volt systems because they work. These are the same connectors used on the major airliners ... 747's etc, they use them for the same reasons - they work.

> If you wish to go even further to insure equal voltages, you can
> "CrossConnect" the bank ...

This is an unnecessary complication that eliminates redundancy and versatility. It could make underway repairs very difficult to do.

> The hydrometer is the last word in state-of-charge.

Yes, on a per cell basis. The digital multi-meter is the best quick check of a battery or battery bank.

> Do an equalize charge at least once a month - every two weeks is better.

The last time I discussed this with battery manufacturers and charging systems manufacturers, they recommended a FULL CHARGE [i.e. controlled current until batteries reach a particular voltage; takes longer than normal] every two weeks and equalization only when the amp hour capacity begins to decline.

From Norm on the IRBS live-aboard mailing list:
I have to disagree on [someone's proposed] two bank house battery scheme.

When a bank needs recharging, you can recharge it and still support loads.

Recharging one 220 AH bank separately is the same wear and tear as it would be charging two banks in parallel. Provided your charger can keep up, the battery has no way to know how many batteries are in parallel with it.

I can see no efficiency disadvantages in using two banks per se, except for some losses in the switching arrangements in the charge and discharge circuits, but the additional complexity of switching the load and the charger from bank to bank makes it more likely that a bank will be either over discharged or under charged from time to time. Chronic undercharging is the biggest cause of premature battery failure.

It appears to me that the advantages of redundancy are small compared to the likelihood of problems due to switching complexities. For example, since we normally only discharge to the 50% floor, there is plenty of reserve power (Trojan recommends no more than 80% of capacity for best life so the 50% level is quite conservative) left in the batteries when charge time comes around. And if you are set up with solar and/or wind there is the distinct possibility of only occasionally reaching the 50% discharge floor if you have enough RE power to keep up with your loads.

I can't see how allowing one bank to wait until is called up again will do any good. Any advantage gained by using each bank for half the time may be more than lost by pulling twice the amps when discharging from that bank. Machines do not have to "rest" between uses, in fact most machines are "happier" in continuous, moderate loads because operation parameters, mainly temperature, stabilize. Large temperature changes are not well "liked" by machines in general.

But the strongest reason I can offer is that it just isn't done by people who live on batteries on a daily basis. I have lived for two and a half years with a single house bank (recharged every day or two with a genset). In addition, the community of Home Power readers, thousands of whom live on batteries, all use single banks of batteries. Of the scores of systems I have read about in Home Power and the many liveaboard boats I have been aboard, it just is not done.

In my experience the biggest factors in satisfactory battery operation is buying high quality batteries (I prefer Trojan, but I hear Surette makes fine batteries too), insuring they are fully charged at each charge cycle, and maintaining a "hands-on" relationship with your batteries.

About every two weeks I do an equalizing charge (with genset and Trace inverter/charger) on my house batteries (we also do laundry and make water at the same time). Then I pull all the caps and check the specific gravity (and insure there is electrolyte enough) in each cell. They are 1.280 when equalized. When I put the caps back on I wipe any dripped acid off, then mix a little baking soda into water and apply it carefully to the battery tops and terminals with a paint brush, wiping off the neutralized acid as I go. Finally I smear a little baking soda laced Vaseline on the terminals.

I don't do a regular equalizing charge on the 8D starting battery and the genset alternator keeps it charged up, but I do the hydrometer check monthly then carefully wash the top of the battery off with the engine room fresh water hose.

One more thing. I found that simply setting the charging parameters on the Trace is not enough. The voltage levels I programmed into the Trace are not reflected at the battery. After discovering my house batteries were not being full charged, I found that I had to measure the actual voltage on the battery terminals and set the charger somewhat higher to produce the voltages that Trojan recommends at the battery. And yes, the Trace does have voltage sensing wires going to the battery (and a temperature sensor). Such is the real world ...
From Larry DeMers on the IRBS live-aboard mailing list:
I understand your point of view, paraphrased in this summary. You don't like a multibattery house bank because:
1. too complicated and could lead to confusion sometime.
2. Redundancy is not important enough to cause the extra complications.

My response is that redundancy to a sailor is far, far different than it is to a home power user. He is at home already, and will not suffer unusually if his power should fail due to battery failure or some electrical problem. To me, redundancy is absolutely necessary on a boat that leaves the dock much. I do not count on luck, therefore the high degree of redundancy on my boat.


From Bruce Wachtell:
The conventional rule of thumb for discharge of deep cycle batteries is 50%, but this rule is a little deceptive. What is more important than the degree of discharge is the recharge environment. In the automotive environment, little or no damage is done during deep discharge. You can take a totally discharged battery and recharge it to its original specification provided you keep the battery absolutely still during the recharge process. Once discharged the irreparable damage is done by shock vibration that results in the lead sulfate precipitate on the plates sloughing off and dropping to the bottom of the cell, never to be reconverted. This is particularly true with conventional rectangular lead plate batteries. The AGM technology mitigates this potential by the use of glass mats that helps to keep the lead sulfate on the plates. In any event, the worst thing you can do to a discharged battery is to jump start it and go bouncing down the road. The only beneficiary of that behavior is the battery company.

Battery charging stages:
  1. Bulk: charge at high current until about 75% charged.
  2. Acceptance: reduce current steadily and keep going until 100% charged.
  3. Float: maintain fully-charged battery.
  4. Equalization: overcharge at low current until voltage stops rising, to remove sulfation.

West Marine's "Smart Battery Charging"

Wiring affects how much current is drawn from each battery:
SmartGauge's "Interconnecting Batteries"

From Susan Meckley on The Live-Aboard List:
I would strongly suggest that you consider a "battery combiner" also.

It is an item that is connected between the positive terminal of the start bank, and the positive terminal of the house bank.

Whenever a higher-than-normal voltage (i.e. charging) is detected, both positive terminals are connected together. However, when the voltage drops back to normal (i.e. not charging) the two banks are isolated.

The benefit of a combiner, rather than an isolator, is that the isolator is old technology and has a 0.7 VDC voltage drop, while a combiner has only a 0.07 VDC voltage drop [at alternator max output current; goes to zero at trickle/float].

My experience:
I bought a Blue Sea Systems "120 A SI ACR", part number 7610, in 3/2007.

Installing it was fairly easy: you insert it into positive cable run between starting battery bank and rest of system (charging sources and house batteries), and have a separate positive cable from starting battery bank to engine starter motor solenoid. Plus two thin wires: a ground wire from combiner to system ground, and a "starting isolation" wire from small terminal on engine starter motor solenoid to combiner. This lets the combiner isolate the batteries the instant it sees voltage in the starting circuit when you turn the ignition key.

One thing that causes some head-scratching before installation: it doesn't matter which side of the combiner (A or B) the starting batteries are on. It combines if it sees charging voltage on either side; after thinking about it for a while, that makes sense. The device is symmetrical.

One thing I like about this particular combiner: it combines when it sees 13.0V on either side. The West System and Yandina combiners combine at 13.3V, which seems a little high to me. I guess it depends on what kind of charging you do; I often use just solar, and on some days it doesn't often get to 13.3V.

From Gary Elder:
A couple of thoughts about your 12v system: If it is time to replace your batteries, consider replacing your old charger with a properly sized new 'smart' charger at the same time. A high output alternator with it's own smart regulator is a good idea also, if you plan to be away from shore power much or if you plan to use a lot of amp hours. Batteries 'like' to be fully charged at least every 2 - 3 weeks and your old ferro-resonant charger and old regulator are not capable of ever doing a full charge. Each time you exceed that magic 2 - 3 week interval, it becomes more difficult to do a full charge - eventually the battery plates become so 'sulfated' that a full charge is impossible. Pricey stuff, but the new batteries will like it.

You may also want to consider that 4D and 8D batteries are real dinosaurs of battery design. Essentially, they are truck/bus starting batteries that will withstand some deep cycling.

I am a big fan of golf cart batteries because they are true deep-cycle batteries that give lots of bang for the buck. Trojan T105 is my favorite. The downside of these batteries is that they require modifying the battery box. Not a big deal, just a minor irritation.

From Garbonzo on Cruising World message board:
First of all, all batteries are not alike, as you know.

The slower and more gently you charge a battery, in general, the longer it will last. But all types of batteries have characteristic maximum charging rates and maximum set point voltages above which they will be very unhappy. For example, a deep-cycle battery of flooded cell design (eg golf cart type) has a max charge rate in the 15-25% percent of capacity so you could perhaps charge a 400 amp-hour bank at a sustained rate of 75-100 amps. Gel cells and AGM type batteries can tolerate somewhat more, up to 40% or even higher, but of course they are much more expensive. Gassing voltage for gel cells which represents the max voltage that can be applied is in the 14.2 to 14.4 region. I don't recall what it is for flooded cell batteries but it may be higher.

An automotive system is designed around keeping a mostly full battery fully charged, and supplying all of the vehicles power needs when the engine is on.

A marine charging system, as least in the typical case on this board, attempts to charge a deeply discharged battery up to full capacity in the shortest time period without frying it.

These are very different purposes. The alternators are really not that different except that marine alternators (on a good day) are designed for relatively long periods at high amp rates, eg. 70-150 amps for 3 hours or so.

The regulators (three step) are designed to charge fast and safe. They do this by applying maximum field voltage to the alternator early in the charge (Bulk Charge Step), hold a constant voltage (eg 14.4 volts or higher depending on battery type) and decreasing alternator current for a specific period of time (Absorption Step) and then dropping to 13.7 or so volts on the Float step. There are many variations to this theme, but they all intend to put the most current in amps-hours back into the battery in as short a period of time. The good regulators are temperature compensated so they vary the applied voltage to suit the battery temperature.

From Larry Janke's "Knowing your batteries - Part 4" on Sailing World:
[Why you shouldn't use a cheap single-stage charger from an automotive store:]

These chargers are not appropriate for charging deep-cycle battery banks as they charge slowly and cannot fully recharge to rated battery capacity in any reasonable period of time. There are no automatic current or voltage adjustments during the recharge cycle and without constant monitoring, the single stage charger will excessively gas the battery, causing electrolyte loss, and may overheat and warp the plates causing premature failure.

... charge current drops quickly, necessitating very long charge time, and if you are not there to monitor the process your batteries will pay the price. Additionally these chargers usually have steel cases not well suited to the marine environment, are not ignition protected and utilize inexpensive minimal specification transformers to drop the voltage from 120 to 12 volts rather than isolation transformers utilized in quality chargers designed for marine applications. A further problem in that the DC negative and AC neutral are connected, with the subsequent potential hazard of electric shock, severe injury or death. Neither are they ignition protected, especially important in gasoline engine powered boats. A final and important drawback is that these types of chargers will allow substantial amounts of alternating current known as AC ripple to pass through into the batteries, a condition which is very destructive to battery plates. AC ripple should not be more than .5% of float voltage. These chargers do not belong on boats.

From Jim Manzari on the IRBS live-aboard mailing list:

If you're interested in treating batteries better, I would suggest limiting discharge to no more than about 80-90% of full capacity. The total number of charge-discharge cycles, before capacity is seriously reduced, varies according to the depth of discharge. For a typical deep-discharge lead-acid battery ...

Depth of dischargeCycles

From John / Truelove on the IRBS live-aboard mailing list:
This is just impractical, IMHO. At first, I was like Scrooge, asking "Do you really need that fan on?", baby-sitting the Link 2000 like a new-born, and praying for more wind and/or sun, trying to keep the "% remaining" high. As far as I know, Heart, Trojan (and others) still recommend that for live-aboard marine use, 50-85% is the target and it seems to work for us. At 80%, we would have to limit our use to 132aH before recharging. As conservative as we are, that isn't enough, and charging from 80-100% takes a loooooooooong time. T-105s are $60 in Trinidad, and most whom I've talked to get 5 years out of 'em, and most don't have 4-stage chargers. That's $6 per month for a 660aH bank, not too bad, IMHO!
From PVB on Cruising World message board:
The best-kept secret of 12 volt systems is that the bigger the battery bank, the fewer the problems. With a really big amp-hour capacity, routine discharges represent quite a small percentage of total capacity, so the battery bank's life is dramatically extended. Additionally, it's much easier to pump amps back into a big bank, so recharging is speeded up. ... A couple of years back, I upgraded my system with a 660 amp-hour bank, and I haven't had any battery problems since. If I had room, I'd put a few more batteries in.

From Lyn Williams on The Live-Aboard List:
Having more than one bank of batteries and switching between them has one saving feature - if any kind of disaster overtakes one bank of batteries, then you just MIGHT have a backup bank, depending on your charging system and maintenance program.

Arrayed against this possible saving feature are some disadvantages.

1. Battery life is affected greatly by percentage of discharge. If you put all of your batteries into ONE bank instead of two, then your percentage of discharge is less so your batteries WILL last longer.

2. If your charging system is such that it only charges one bank at the time, then there is a possibility that the alternate bank will not be charged as frequently as it should. Lead-acid storage batteries do self-discharge with time, at a rate which depends on battery construction. Older battery types typically self-discharge at a rate of approximately 5% per week. This is probably the source of the old wives tale that a battery sitting on a concrete floor will be discharged by the concrete. After a week of self-discharge, sulfate crystals are already getting large enough to reduce the useful lifetime of the battery, especially if the battery is then subjected to stresses like bouncing or excessive charging.

From Dennis / True Mettle on the SailNet liveaboard-list:
I have a SGC-2000 ADSP SSB radio. On transmit it draws 25 amps, on receive it draws 2.5, on standby without the crystal oven heater turned on it draws 1.0 amps. With the Pactor-II modem I can download mail in under 1 minute with 80 percent transmit cycle. With Kantronics KAM+ the same thing takes about 3 minutes with about 60 percent transmit. I normally use the radio to pull email once a day, I check in to the Pacific Maritimers Net every day, and I pull a weather fax down about 3 times a day.

In amp hours I don't really know what this actually runs. I have an E-meter on the boat and it tells me that the 6.5 amp fridge, 8 hours of anchor light, 3 hours of TV and 2 hours of reading lights, unknown number of minutes water pumps etc take about 150 amp-hours/day. This is realistic due to my power demands. I do have an 880 amp/hour battery stack (440 usable).

My RADAR draws 2.5 amps but I only put it on at night or fog, my nav lights take another 4 amps, the VHF (for the amount I use it) draws just under an amp on RX, I have not measured the power draw on TX as it's infrequent unless I am involved in some kind of rescue.

I recharge the batteries in the morning of the 3rd day with 3 hours of 150amp/hour alternator but I can safely go 5 days before things start crashing due to low battery voltage. The biggest killer of power is my laptop inverter. The little 90 watt inverter draws 9 amps when loaded up.

From sidebar by Ed Sherman in 12/1999 issue of Cruising World magazine:
... you shouldn't rely on voltage readings taken immediately after charging to determine a battery's actual state of charge. For that you need to either let them settle out for a while or put a load on them to remove the surface charge. Settle out for how long ? The "stabilization period" varies ... half an hour to 48 hours ... three hours usually does the trick.

From Gary Elder:
For wet-cell batteries only:
12.70 volts == fully charged
12.45 volts == 3/4 charged
12.20 volts == half charged
11.95 volts == 1/4 charged
11.70 volts == fully discharged
From Clymer Mercury outboard manual:
For wet-cell batteries only, unloaded, after resting for 30 minutes:
12.7 volts == fully charged
12.4 volts == 3/4 charged
12.2 volts == half charged
12.1 volts == 1/4 charged
From "Electrical Tests and Repairs" article by Tom Wood in 4/2001 issue of Sail magazine:
For wet-cell batteries only, unloaded, at 97 degrees Fahrenheit:
12.67 volts == fully charged
12.34 volts == 3/4 charged
12.04 volts == half charged
11.80 volts == 1/4 charged
11.68 volts == fully discharged

At 77F, all values are 0.04V lower than those at 97F.
At 57F, subtract another 0.04V.

From "Electrical Tests and Repairs" article by Tom Wood in 4/2001 issue of Sail magazine:
Hydrometer reading, for wet-cell batteries only, unloaded, at 97 degrees Fahrenheit:
1.272 == fully charged
1.217 == 3/4 charged
1.167 == half charged
1.127 == 1/4 charged
1.107 == fully discharged

At 77F, all values are 0.007 lower than those at 97F.
At 57F, subtract another 0.007.

From Trojan User's Guide: "Open circuit voltage testing is the least preferred method of evaluating the performance of a battery. ... For accurate voltage readings, batteries must remain idle at least 6 hours (but preferably up to 24 hours)."

From HandyBob:
How about this revolutionary idea: If you want to know how to charge a battery, try looking at the battery manufacturer's recommendations instead of believing the charger manufacturers. On Trojan's web site you will find that they recommend a 14.8 volt daily charge, not 14.4 like everybody else will tell you. They also say to continue charging at that voltage until a specific gravity test shows the battery to be full, not to shut the charge off immediately or even early like most chargers operate. Interstate will tell you similar things. The popular opinions on charging AGM or other sealed batteries are also wrong. Every charger I have seen, as well as every solar charge controller, is set too low. I have heard people say that this last .4 volts is insignificant, but they are very wrong. Oh, you can charge at 14.4 volts if you are plugged into shore power for days, but running the generator for a few hours or having your solar controller shut off as soon as it reaches the set point does not work. ...

[But this may have to be temperature-compensated. For example, Link 2000 manual says accept voltage for flooded batteries is 14.8 V at 50 F, 14.4 V at 70 F, 14.0 V at 90 F.]


... Wire that is not way oversized will not efficiently transmit DC power to your batteries. (Look up the history on Edison vs. Westinghouse; there is a reason we don't use DC power transmission.) ...


A $200 recording "smart" meter like a Trimetric 2020 or a Link is a necessity if you want to boondock on battery power in an RV. It is the water level gauge for the batteries and tells you the actual level of charge. This will tell you if your charger is actually working (converters powered by generators do not) and when to run it. Cover the voltmeter with a piece of tape.


Buy a three-stage charge controller that is adjustable and set it as recommended by the battery manufacturer (14.8 V if you have wet cell golf cart batteries). ...


Insist on the charge controller being located as close to the batteries as possible. In no case should it be even six feet away. The voltage drop between it and the batteries will prevent your expensive power from reaching your batteries and getting them fully charged. Also, insist that the wire between the controller and the batteries be oversized, at least one size larger than required by the amp rating in order to limit the voltage drop to less than 1%. The wire from the roof to the charge controller needs to be sized for a maximum of 3% voltage drop. The overall drop, panels to batteries, needs to be close to 5 or 6%. ... The voltage drop from the panels to the controller doesn't hurt if kept to a reasonable level, but from there to the batteries it is critical.


FUSING: This just flabbergasts me, but I run into unfused wiring all the time in RV's, some of it installed by the original RV manufacturer, and some installed by "professional" RV technicians. I say "fuse" on purpose. I don't like the automotive-type automatic circuit breakers. First, you can't turn them off like you can pull a fuse for disconnecting; and second, breakers are mechanical devices that are prone to failure. I have also found a few that were drawing a phantom load. Don't use the in-line fuses with springs behind them for a heavy, constant load like solar charging. They tend to get warm and eventually melt down. This is true even for the larger ones in a clear plastic case that the solar dealers sell. I use the big stab-in automotive type or the 250 V cartridge type commercial fuses and holders. One of the folks I sent this to came up with a brilliant suggestion for fusing the solar leads; a two-pole fused air-conditioner electrical box with a pull-out disconnect. They are available 30 and 60 amp and have #4 lugs for the big wires we need to use. Connect the input from the panels to the controller on one side and the output from the controller to the batteries on the other. Disconnecting the entire solar system is then one simple motion. They are dependable and cheap. The bottom line is that every single positive wire needs to be fused within inches of the battery so that it will be protected should it ever rub against something metal and cause a short, starting a fire, or worse. Batteries have been known to explode if shorted to ground.

Battery Monitors:
These monitor the battery voltages and the currents in and out of the batteries. Some of them count amp-hours in and out. Some have proprietary integrations with battery chargers and inverter/chargers. Some act as alternator regulators too.

My experience:
I bought a Heart Link 2000 in 4/2002. (Don't buy the "wiring kit" they offer; it is an overpriced piece of twisted-pair wire. Make your own by twisting stranded boat wire.)

Installing it was fairly easy: you wire the negative cable from each battery through a "shunt" that comes with the battery monitor, several small wires go from shunt to monitor, several small wires go from battery positives to monitor, and the monitor panel has to be mounted somewhere visible. If space near the shunt is tight, it is easier to connect the small wires before the big cables.

Works like a charm. But solar-charging or wind-charging defeats the automatic tracking of amp-hours used since last charge: it expects one big engine-charging session and then a long series of discharges, and doesn't understand many small discharge-charge cycles. Not a big deal.

I wanted digital number readouts, not LEDs that indicated coarse levels such as 0/20/40/80/100 percent.

Sometimes it's hard to figure out all the piece-parts you need to order; some suppliers list the shunt separately.

For the very popular Xantrex products, price-shop around the internet. I found Heart Link 2000 prices ranging from $500 at West Marine to $350 at SailNet in 2002.

Some suppliers:
Ample Power
Cruising Equipment

Battery problem diagnosis,
summarized from "Boatowner's Mechanical and Electrical Manual" by Nigel Calder:
  • Full voltage under no load, and steadily falling voltage under load: low on usable capacity; if voltage comes up quickly on charging, limited amount of active material left on plates.

  • Wet-cell that never needs topping-up with water: battery is being undercharged.

  • Wet-cell that needs frequent topping-up with water: battery is being overcharged.

  • Wet-cell with one cell that needs frequent topping-up with water: cell is shorted.

From Arild Jensen on The Live-Aboard List:
> suggestions on testing batteries and their charge-holding
> capabilities? How do we determine how 'tired' they are?

For this test I use an old electric clock and a small 300W inverter driving a 100 watt 120 volt light bulb. The small inverter has a low-voltage cut-off point of 10.5V which is considered the dead battery point by most battery manufacturers. The 100W bulb produces a 10 amp draw on the 12V side of the inverter. If you prefer the 20 amp curve, use a 200 watt bulb. The electric motor clock is simply there to let you know the elapsed time of the test so you don't have to stand there watching. I set the time to 12:00 at start and the clock will stop when the inverter cuts off at the 10.5V low point. The inverter acts to maintain the constant current draw of 10 amps over the duration of the test. Don't use a big 2000 watt inverter for this test since the idling (parasitic load) current will skew your results.

My opinion: how to tell if your batteries are worn out:
Your batteries are "worn out" of they start acting like much lower-capacity batteries; that is, if they start charging and discharging much quicker than usual. For example, if when new, your batteries charged from 12.3V to 13.8V in an hour, and now they charge that much in 15 minutes, they are acting like they have much less capacity than they did before. Same going the other direction.

From Norm on the IRBS live-aboard mailing list:
The Equalizing Charge

In many of the inverter/charger applications, batteries are subjected to less than ideal operation conditions. This can result in significant differences in the state-of-charge level between the individual battery cells. Furthermore, the low charge rates and extended periods at partial charge levels can result in both stratified battery electrolyte and inactive areas of battery plate material. If the condition is allowed to remain for extended periods of time, the battery can "sulfate" and become unusable.

To correct this condition, many manufacturers recommend a periodic "equalization" charge to mix up the electrolyte, re-activate unused battery plate material, and bring up all of the individual cells to a full state of charge. This requires that the battery be given a controlled "overcharge" by increasing the charge voltage for a limited period of time. The voltage and time required are both dependent upon the amount of correction required. The more frequently the batteries are equalized, the lower the equalize voltage and shorter the time period.

Equalizing a battery is only recommended on unsealed or vented batteries. The process will cause the electrolyte to gas and will release hydrogen and oxygen in the process. The chance of explosion due to the accumulation of these gasses is therefore a realistic hazard. Thus batteries must be provided with good ventilation and no ignition sources must be present. Some users have found that the battery cell caps are subject to clogging during an equalization charge and therefore remove them during this process. Since the batteries may rapidly bubble while being charged, it is advised that the battery be refilled only after the equalization process is finished (if the battery electrolyte level is low, add enough to cover the plates before charging).

The battery manufacturer or supplier should be consulted before equalizing to provide the recommended process and settings. Every hour the temperature of each battery should be checked by momentarily feeling the battery case with your hand. If the batteries become excessively warm (too hot to keep your hand on) during the equalization process, terminate the charging immediately. Let the batteries cool before checking the need for further equalization charging.

(the above quoted from the Trace 2512 inverter/charger manual by Trace Engineering, (360) 435-8826, makers of high quality inverters)

The Equalizing Charge

When the individual cells in a lead-acid battery begin to show differences in their states of charge, it is time to run an equalizing charge. These internal differences result from differences in temperature and rates of local action between cells. These differences can be measured in either voltage or specific gravity. The only cure for these inequalities is a controlled overcharge of all cells - the equalizing charge.

In order to equalize a battery it must first be fully charged. The state of charge of the battery may be determined from Fig. 2-12 (buy the book! - - Norm). The voltage limit is then raised to 2.75 volts for a single cell, corresponding to 16.5 volts for a 12 volt system. This voltage is dependent on temperature and will have to be raised for cold batteries. The battery charge is continued at the C/20 (C = the capacity of the battery bank in amp/hours) rate for 6 to 10 hours, or until all inequalities in the cells are eliminated. The equalizing charge is actually a constant current overcharge. Equalization should not be carried out at rates greater that C/20.

Caution should be observed as the system voltages, while equalizing, are quite high. A 12 volt system may reach over 16.5 volts during equalization, much too high for many 12 volt appliances. Be sure to turn off all voltage-sensitive devices during the equalization charge.

During the equalization process, the battery will gas profusely. Care should be taken to provide adequate ventilation during all charging processes, especially during equalization. The gasses (hydrogen and oxygen) emitted from a lead-acid battery during charging are explosive. Keep flames and sparks well away from the battery during all charging. The more rapid gassing during equalization results in increased water consumption of the cells - keep your eye on the electrolyte levels.

If equalization is not periodically carried out, the weaker cells within the battery pack will become overdischarged and wear out quickly. Lead-acid deep-cycle batteries should be equalized every five to ten cycles or monthly, whichever comes first. The same equalization is necessary for lead-acid batteries in float or shallow cycle service.

Equalization can be used to restore some of the capacity of aging batteries. It is also effective in dealing with the sulphation which results from sitting discharged for extended periods of time. If the batteries are in very poor condition, they may take up to five equalizing charges to restore them to service. The equalizing charge will not restore totally worn out batteries, but it will help us keep our batteries working efficiently for as long as possible.

(quoted from "The Complete Battery Book" by Richard Perez, editor of Home Power magazine)

From John Bierrie on the IRBS live-aboard mailing list:
The information Norm provided concerning equalizing batteries is good and accurate as far as it goes. There are two items which should be mentioned though.

1. Never, never, never (emphasis!) try to equalize a Gel Cell battery! The resulting explosion could cause serious injury, death and property damage. See U.S. Coast Guard Warning statement # 78 (I believe) for details.

2. AGM batteries can and should be equalized, but at different settings and timing than wet type lead acid batteries. Lifeline / Concorde recommends that their AGM batteries be equalized on a yearly basis. The equalization voltage of 15.5 volts should be applied for 3 hours at a rate not to exceed 2-4% of the battery's amp/hr capacity. At no time should the voltage exceed 16 volts. Though the batteries will not explode from this, they will be killed very quickly. Note: any battery "can" explode, but AGM's are less likely to ...

Lifeline's AGM batteries additionally do not tolerate being completely discharged very well. Should they ever be put in this condition, it is likely that their capacity will be severely affected. You will notice that though the batteries will accept a charge, the capacity will quickly (far more so than normal) dissipate (either at rest or under load). Should this happen, you will need to equalize the batteries, use them for a week or two (discharging at least 25% between charges) and then equalize them again in order to get their capacity back to normal.

From Richard on the IRBS live-aboard mailing list:
Never never let an equalize charge run free. At least it must have a timed shutoff (about six hours). Most recommend that the user turn off the cycle when the SG of the batteries is equal.

From John / Truelove on the IRBS live-aboard mailing list:
I happened to meet Heart's International sales manager in Trinidad last May. One of the things he told me was, "People equalize way too much. Once or twice a year is enough. Once a month is too much and is detrimental to the longevity of the batteries." I have been out of the loop on the latest thinking on this subject, so perhaps someone on the list can shed some more light on this.
From Larry DeMers on the IRBS live-aboard mailing list:
I agree with you. Equalizing once every 6 months is plenty, but that would be modified by your use and battery size and demand. If the bank is small, the demand high, then perhaps you are used to deeper discharges, and these create more sulphation on the plates ...

From Andina Marie Foster on The Live-Aboard List:
The word equalization is thoroughly misunderstood and misused. Naming pulse devices and liquid battery magic as equalization products is totally misleading.

Equalization is not intended to desulfate batteries.

Equalization is not intended to stir up electrolyte.

Equalization is not intended to prevent stratification.

Equalization is primarily charge EQUALIZATION as the name indicates.

It is intended to equalize the charge in the individual cells so they all have a matched capacity. Like a chain, your battery is only as good as the weakest link (cell). When the weakest cell is discharged, no more current will flow through it, and if it does, then permanent damage is done to that cell. Despite good controls, the cells in a battery don't match exactly when manufactured. So when you charge to say 14.2 volts you don't have exactly 14.2/6 = 2.37 volts on each cell. The weakest cell is going to have less and the others will have more. So each time you use the battery this weakest cell gets the deepest discharge and will tend to age faster, making the situation worse. But if you stop charging at say 14.2 volts, you never get the weakest cell back to full charge.

EQUALIZATION equalizes the cells - that is where the name originated. By charging the battery to a higher voltage you intentionally overcharge all the good cells in order to force charge into the weak cell(s) and get them back to full charge. The overcharged cells can't get more than 100% charge so they gas and bubble due to the overcharging while the weak cell charges up. They all then start the next discharge cycle EQUALLY from 100%.

It is true that the gassing and bubbling during equalization has other benefits, although the cell that needs it the most is probably still charging and not getting any benefit from the gassing and bubbling.

So if you use pulse devices to decrease sulfating they do NOTHING for equalization. You can't substitute a pulse device for equalization.
From Craig Parsons on The Live-Aboard List:
However equalisation does, through a controlled overcharge, help dissolve solidified sulfate deposits amongst other things - by default it achieves all the items in your "not intended to" list - my understanding was that the individual cells were not in equilibrium because of the sulphate deposits on the plates?
From S/V Princess Thalia on The Live-Aboard List:
That is correct, when the batteries lead plates are coated with sulfur, they allow much of the current to create the chemical reaction bring the viscosity of the sulfuric acid up and charge the cell. Eventually the acid turns in to clear water and just boils without any results.

Battery Equaliser ($20 for 12 oz; "A small amount of Battery Equaliser added to each cell will mix with the existing electrolyte solution. The improved battery chemistry will dissolve existing sulfation and prevent new deposits from forming for years to come. Follow normal battery maintenance and double battery life with only one treatment.")

From Andina Marie Foster on The Live-Aboard List:
... in the past, liquid battery rejuvenators have been a target for various scams so at the risk of doing harm to a good product I strongly suspect it provides no benefit too. Had a chemical been available to magically restore batteries it would be on every WalMart shelf. The attraction for scam is that it is very difficult to evaluate without extensive scientific testing.

"8D" and "Group 27" refer to the physical size of a battery; see BCI Battery Group Size Chart.

Paraphrased from "The Boatowners Mechanical and Electrical Manual" by Nigel Calder:
  • A typical deep-cycle 8D battery has a capacity of 200 AH and weighs about 150 pounds.

  • Batteries in parallel are bad: one dead cell pulls down all, and self-discharge increases.

  • Battery capacity should be 4X the demand between charging; charging capability should be 1/3 of battery capacity, plus any extraneous load during charging.

  • Keep electronic equipment away from batteries (corrosive fumes).

  • Need good ventilation to dissipate battery heat while recharging (sparkproof fan directed at base of batteries).

Golf-cart batteries:
6V golf-cart batteries better than 12V deep-cycle batteries:
  • Less weight per battery (60+ lb for 6V, 100+ lb for 12V).
  • Plates may be thicker (many 12V's are thickened car batteries ?).
  • Slightly cheaper per AH, for some reason (maybe production volume ?).
  • Less to replace when a cell dies or a case cracks.
  • Can fit them into odd-shaped compartment.
  • Require more cables/connectors: more potential corrosion and current-loss points.
  • Nobody makes cheap battery boxes for golf-cart batteries.

Golf cart battery approximate (they vary) physical size: 10 1/4" wide by 7" deep by 12" tall.

Most golf cart batteries are approximately 220 AH.

From Greg Hanka on the IRBS live-aboard mailing list:
Golf cart batteries are deep-cycle batteries *plus* vibration resistance. Since vibration is a major killer of flooded cells, especially on boats, vibration-resistance will hugely prolong their life -- up to the level of gel cells (which are inherently vibration resistant). The fact that golf cart batteries are 6V is an accident of market inertia. They could just as easily be 12V and still be vibration resistant -- in fact, some of the larger traction batteries are. It's not an issue of voltage or plate thickness or plate count; it is something else, such as paste composition or grid layout.

The low price of golf cart batteries makes them the most cost-effective type of flooded battery available. ...

From Norm on the IRBS live-aboard mailing list:
Golf cart batteries are excellent for house batteries. They are made for deep-cycle use. "Marine" batteries are a nonsense, advertising, term designed to get more money from you. Golf cart batteries, which are a generic deep-cycle battery, are made with fewer, stronger, plates and are designed for deep discharge. ...

[But "Stowaway" brand is bad, Trojan is good ?]

From Lyn Williams on The Live-Aboard List:
I like my combination of two Trojan 6V golf-cart batteries in series, with that combination wired in parallel with an identical pair. This results in 450 AH of storage capacity at a cost of just under $50 per 6V battery (cost when I bought them 3 years ago). However, this system is not for those who can not take time to learn about and give proper care to their batteries.

Don't even think about trying to use automotive batteries for sailboat applications. If the battery specs include phrases like "cold cranking power" or "marine cranking amps", you are looking at an automotive or marine starting battery, while a sailboat needs a deep discharge or deep-cycle battery. A deep-cycle battery will have an "AH" (ampere-hour) rating displayed prominently. If don't see the AH rating without asking about it, chances are that it is not a deep-cycle battery.

An automotive battery is not rated for deep discharges, but is designed to put out a high current for a very few seconds -- followed by almost immediate full recharge. By discharging the battery a deeper percentage without immediate recharging, you are actually using up the life of your battery and hastening the day when the replacement must be bought.

In order to make a series/parallel system work well for an extended time, you need to keep all the batteries identical by starting with all new batteries at the time the system is set up, and monitor them carefully to make certain they stay very similar in performance.

Be very careful to follow the good book about rates of charge and discharge. Deep-cycle batteries are typically rate to deliver a certain discharge rate for 20 hours. If you discharge at a faster rate than 5%, part of the stored charge will be converted to heat and will be wasted.

Keep the percentages of discharge as low as possible - trying to stay under 10% - but never over 50%.

Battery discharging is where you have a major influence on the life of your battery. The percentage of discharge before recharging has a major effect on battery life. A battery which is rated for 350 charge/discharge cycles to 50% of capacity may be able to withstand thousands of charge/discharge cycles if the discharge percentage is limited to 5 or 10 percent.

A good way of killing a battery is to frequently leave it partially discharged for several days. Battery life time is greatly affected by the length of time the battery is permitted to stay partially discharged (just as close to zero time as you can arrange, and never more than a day or two).

You will need a good digital voltmeter to monitor your battery; the old-fashioned analog meter scale is not good enough if you wish to get maximum life from your battery.

You will need to learn the relationship between the battery terminal voltage and the state of discharge of your battery. While the exact numbers depend on the manufacturer's specs, lead-acid storage batteries are typically fully charged if the terminal voltage measures 12.7 volts 24 hours after the last charge or discharge operation. Similarly, they are fully discharged if the voltage is 11.7 volts 24 hours after the last charge/discharge operation. Within 24 hours of either a charge or discharge operation, measuring the terminal voltage will not show the true status of the battery.

There are several important phases during the charging operation. Learn them well if you wish to minimize your replacement costs. Improper charging is one of the fastest ways of killing a good battery. Follow the manufacturer's suggestions. Reputable battery manufacturers have data sheets showing all relevant battery specs, as well as technical sheets describing correct charging procedures. If your battery manufacturer is not willing to produce these sheets, then you have obviously chosen the wrong battery manufacturer.

Using tap water instead of distilled water to replace evaporated liquid is another way to kill a battery.

From Rick Morel on The Live-Aboard List:
I don't think you can beat golf cart batteries (unless you have room for forklift batteries). Their Amp Hours tend to be "bigger" than others. This odd statement comes from the fact that golf cart batteries are rated at a higher current draw than the others. Note that the more current you draw from a battery, the lower the AH capacity. For instance, one may be 100-AH at a 10A draw, but may drop down to 70-AH at a 20A draw. Those figures are for illustration only, I really don't remember particulars from the time we ran tests on various batteries. This explains the "better draw per minute value" above.

Another thing to note is that many folks state that since golf carts are deep-cycle, don't use them for starting. This is totally WRONG. They're fine for starting. One has to remember they are made to supply current continuously at about 75A and to supply startup currents to 1,000A or more.

I'll end this with the three best ways, in order, to shorten the life of any battery.

1: Continuously overcharge. ie, don't use an auto-cutoff charger and just leave it on.

2: Allow the electrolyte to go below the plates more than once.

3: Continuously allow more than 24 hours to go by with the battery not at full charge.

From Norm on The Live-Aboard List:
Yes, you can use golf cart batteries for starting IF they will deliver the required amps. Starting batteries are made with more, thinner, plates to reduce internal resistance and increase maximum current to dump more current quickly into the starter.

Although I have not heard anything about this, my guess is that if golf cart batteries will start spin your engine properly, even at low temperatures, then they would be better as a starting battery because they are more ruggedly built.

From Susan Meckley on World-Cruising mailing list:
I like 6 vdc wired in series parallel. When a battery fails it is usually only one cell. 12 vdc you throw away six cells. 6 vdc you are getting rid of only 3 cells ... and it is easy to wire around the bad 6 vdc cell till you reach port.

From Norm on the IRBS live-aboard mailing list:
The normal, and most honest, rating for the deep-cycle batteries is the 20 hour amp-hour rating. The most common and useful for engine starting batteries is the CCA (cold cranking amps) rating.
From Don Boyd on Cruising World message board:
... the amp-hour is simply an estimate of what a deep-cycle battery is rated at over a 20 hour discharge rate, so if a battery will deliver 10 amp to a load for 20 hours, it's rated at 200 amp hours. ...

From Greg Hanka on the IRBS live-aboard mailing list:
Finally I've found some plate thickness numbers:

typical automotive: 0.040"
typical golfcart: 0.070" to 0.110"
Trojan L-16 and US Battery L-16: 0.090"
Trojan T-105: 0.090"
Concorde AGM: 0.115"
Rolls CH-375: 0.150"
Rolls 6 CS-25 P (forklift): 0.265"

For what it's worth. This is all I could find on the internet.

Parallel connection:
Batteries shouldn't be connected in parallel permanently: a shorted cell in one of them can cause a huge current flow from the good battery to the bad one, and a tremendous heat buildup.

From Brian Woloshin on Cruising World message board:
I would not recommend paralleling two batteries unless they are both new. Minor differences have developed in the batteries because they have been operating independently. The stronger one will constantly be discharging into the weaker one.

I use four 250 AH 6V batteries in series/parallel to get a 500 AH bank and also have a separate engine start battery. The 500 AH bank has been run this way since new and has run great. I have seen attempts to parallel different size/brand batteries with very poor results.

From John / Truelove on the IRBS live-aboard mailing list:
... We have an AB machine with a small (4 cu ft) well-insulated box. In the Caribbean, the unit runs about 5 minutes out of every 15 and draws 5A. That's 40 ah/day. Realistically, following provisioning, it's much more until the food is chilled, which takes hours of constant operation. I figure we are closer to 75 aH/D on average. ...

Yandina's battery-combiner info
Battery packs for jumping dead batteries, reviewed in 11/15/2000 issue of Practical Sailor.

From Philip on Liveaboard list:
Not all rechargeable-battery chargers are equal. Some will destroy your expensive batteries in a short time. If you have one that charges real fast, watch out. Feel the battery. If it is very warm or, forbid, hot you have a battery destroyer. These NiMH batteries dry out and become useless quickly when charged too fast.

Any charger that will fully charge a AAA 1500 - 2000 mAh battery in less 18-24 hours is highly suspect. Some have temperature regulation and reduce the charging current accordingly. Others regulate the charge rate by voltage; these are more expensive, but will save you money in the long run.

When installing new batteries:
Removing old batteries:
  • Baking soda is your friend. Keep a layer on your hands at all times.
  • Put down plastic sheets to keep acid off carpets.
  • After the batteries are out of the engine compartment, wash battery boxes and shelf with baking soda and water.
Installing new batteries:
  • Check and fill water before installing. Easiest to do it then, and water may be very low because dealer hasn't been topping it off. In fact, check the water level before you buy the battery, in the store.
  • Do full charge before putting loads on.
  • Probably a good idea to do an equalization too.
Discarding old batteries:
  • Use hydrometer to remove some of the electrolyte before transporting them, to reduce the risk of spills.
  • Scrub the outsides with baking soda, and leave some caked on the top, to neutralize any acid that leaks.
  • Wrap them in plastic sheeting before transporting them.
  • Vendor of new batteries may want old ones as trade-ins, to avoid "core charge". Or they may charge a disposal fee.

Zap-Stop Alternator Protector (discontinued ?):
Yandina FAQ
From Colin Foster on Cruising World message board:
The Zap Stop explained:

A zap stop is not a fuse. It is not associated directly with the ignition or battery switch. It connects between any 12 volt circuit and ground with 12 volts across it. While the voltage remains within normal operating limits, it has zero effect, but if the voltage rises too high, it starts to conduct electricity and absorb the high voltage to protect alternator diodes, electronics, light bulbs, etc.

A typical installation point is across the alternator output. Alternators can self destruct if disconnected from their load (battery) while they are charging. The reason is the current put out by the alternator is being regulated by the regulator and it uses battery voltage to determine how much current to produce. If you remove it from the load while it is charging, the voltage suddenly rises since the current no longer has a load to absorb it. This sudden rise is immediately detected by the regulator but it has to change the excitation voltage on the alternator and this process takes a few thousandths of a second before it is again under control. During those few thousandths of a second, the voltage can reach hundreds of volts - enough to self-destruct the alternator and any other electronic devices that were disconnected from the battery with it.

The zap stop can absorb hundreds of amps for a few thousandths of a second and limit this voltage spike to safe limits to provide the protection. All boats should install one across their alternator as a safety precaution, especially if using an isolator or if the alternator output can be switched. With a battery combiner, however, the alternator output is always directly connected to a battery so they are not necessary.

Another place for them is across the bus bar that supplies power to your electronics panel to protect against a voltage spike, in particular for protection from the induced voltage of a nearby lightning strike that just missed you.

They cannot protect against loss of regulation on an external sense alternator where the sense lead becomes disconnected or grounded. Although they absorb the initial spike, if it lasts for more than a few thousandths of a second, the zap stop will overheat and self-destruct too. With say 25 volts across it, and say 200 amps flowing through it, the heat build up is 5,000 watts so it can only absorb this for a few thousandths of a second before overheating.

West Marine sells the Heart brand - price about $25.


A Zapstop will be hard pressed to suppress a large alternator that suddenly goes open circuit under a high load. They have a very limited capacity and will be often destroyed by this kind of overload, but hopefully absorb enough of the spike to save the alternator as they martyr themselves.

Northern Arizona Wind and Sun's "Hydrocaps or Water Miser caps"

From article by Dan McCosh in 4/2006 issue of Sail magazine:
There are new battery-testers on the market that apply a low-voltage AC signal to the battery to measure its internal resistance, which indicates capacity. From Midtronics.

Adding acid to revive old batteries:
Auto-parts stores sell a bottle of battery acid you can add to a battery.

From Bernard Chalecki: "I never heard of a battery needing acid unless you spilled it out."

From Bill:
I wouldn't put fresh acid in my batteries if I were you. I'm not a real expert but I'm going to give you my educated guess about wet cell batteries. Charging batteries, especially when they're charged a little fast, removes water, H2O in the form of oxygen and hydrogen, but the sulfur stays in the battery as a compound on the plates. If you add more acid you'll overload the battery with sulfur which will crystallize between the plates and kill the battery.


SailNet - Kevin Jeffrey's "Electrical Power on Board"
Don Casey's "Electrical Connections"
SailNet - Don Casey's "Electrical Work Rules"
BoatUS Wiring article
David Pascoe's "Tips on Electrical System Use and Maintenance"
SailNet - Chris Brignoli's "Keeping Wiring Woes at Bay" (DC wire crimping/soldering)
Robb Zuk's "Marine Electrical Check List"
12-Volt Systems article by Kevin Jeffrey in 6/2000 issue of Blue Water Sailing magazine
Electrical system checking article by Ed Sherman in 4/2000 issue of Cruising World magazine
"Electrical Tests and Repairs" article by Tom Wood in 4/2001 issue of Sail magazine
"Charting a Balanced Power System" article (how to diagram your system) by Kevin Jeffrey in issue 2000 #2 of DIY Boat Owner magazine
Charging article by Nigel Calder in 9/2001 issue of Sail magazine
DC power audit article by Nigel Calder in 7/2001 issue of Sail magazine
"Simple Device for 9-Volt Power" (12V-to-9V voltage reducer) by Donald Boone in issue 2000 #2 of DIY Boat Owner magazine
the12volt.com's "Technical Information for Mobile Electronics Installers"

Types of grounds (most separate):
  • DC.
  • AC (the green "ground" wire, not the white "neutral" wire).
  • Bonding (tying sea-water-exposed metals to an anode, to prevent corrosion).
  • RF (radio antenna counterpoise).
  • Lightning (want one big, straight path from top of mast to water).
  • Fuel system (filler plate to tank to engine, so no static buildup).

Stan Honey's "Marine Grounding Systems"
Stan Honey's "Marine Grounding Systems"

From Dave Richardson on the WorldCruising mailing list:
... Ensure that all AC grounds are totally separate from ships systems DC grounds. You cannot have common AC and DC grounds. Also ensure that battery chargers and the like don't obviate this isolation. After all installations, disconnect the battery negative end, and double-check with a low-sensitivity voltmeter to ensure there is no leakage path. In fact, this is worth doing any time there is a wiring change, just in case. If AC and DC grounds are commoned you are setting yourself up for high potential (100% positive) of stray currents which eat up props, zincs, through-hulls and anything else including a common-grounded engine. ...
But ABYC and Metal Boat Quarterly's "Corrosion, Zincs and Bonding" say otherwise:
AC shore power should pass through isolation transformer, and then internal AC ground should be connected to DC ground, to the bonding system (if any) and to seawater.
And from Peter Kennedy on rec.boats.electronics newsgroup:
ABYC standard E8 8.5.3 specifically requires that the AC ground and the DC negative be connected together. The simple explanation for this is that if you are sitting on the engine block and reach over to touch the air conditioner, you would like them to be both connected together electrically already so that it is not you that it is making the connection.

DC ground must be connected to sea. If this connection is not through the propeller shaft, it should be established through a "dynaplate".

From John / Truelove on The Live-Aboard List:
Here is what I recommend:

If you have metal thru-hulls do not connect them together or to anything else.

Connect both batteries' negatives to the engine block unless using a shunt such as is furnished with a Heart or other monitoring system. In that case follow their instructions.

Ideally, you will have a Dynaplate or equal on the hull below the mast. If not, consider installing one. Connect the base of the mast to the plate with a *straight* run of 4/0 copper terminated in crimped and soldered ring lugs. If you want to ground the shrouds as well, I suggest you run heavy 2" wide copper strap from the cap shroud chainplates along the inside of the hull to the Dynaplate. Again, run it straight. It's been reported that lightning doesn't like turning corners. I also suggest that you replace the grounding stud on the dynaplate with a 1/2" bronze carriage bolt. There have been reported instances of lightning vaporizing the standard stud, resulting in a hole thru the plate. If you ground the chainplates, attach the straps to the same ground stud point as the mast is connected to. Do not attach anything else to this plate! If for some reason you feel you need another ground plate, install one, preferably far away from this one.

I am not a proponent of connecting the AC ground to the DC negative, or, for that matter, to anything else. Others on the list have stated that they have inverters with internal relays which may connect the AC ground to the DC negative. For this reason, and others, I do not bring the shore power ground aboard the boat. If you wish to, do not connect it to the neutral of the incoming 120 VAC. Connect the incoming AC ground wire only to the case of the inverter, if you wish to. That should result in the AC outlets being grounded.

This now will leave you with the dilemma of how to achieve an RF ground plane for your SSB radio. My advice, based on having tried it almost every other way, is to run two copper straps, one from the transceiver and one from the coupler to the same point on the engine block. If you use a 2-pole breaker on the DC power to the transceiver, and leave it off except when using the radio, you will avoid having the RF ground become an additional DC ground path.

DC wiring:
DC wiring should be color-coded:
BlackNegative mainsReturn wire to battery
WhiteNegative mainsReturn wire to battery
RedPositive mainsMain power
GreenBondingNon-current boat bonding system
Dark grayNavigation lightsFrom switch or fuse to lights
Dark grayTachometerTachometer sender to gauge
PurpleIgnitionIgnition switch to coil and instruments
PurpleInstrument feedDistribution panel to instruments
Dark blueLightsDistribution panel to lights
Light blueOil pressureOil pressure sender to gauge
BrownGeneratorArmature to regulator
BrownAlternator charge lightGenerator or Alternator terminal to charge light
BrownPumpsSwitch or fuse to pump
TanWater temperatureTemperature sender to gauge
YellowGenerator or AlternatorField to regulator field
YellowBilge blowerSwitch or fuse to blower motor
Yellow with red stripeStarterSwitch to solenoid
OrangeAccessoriesAmmeter to alternator or generator output, and accessory fuses to switches
OrangeAccessory common feedDistribution panel to accessory switch
PinkFuel gaugeFuel tank sender to gauge

  • Use a separate negative return wire for each device; don't use boat's metal frame as electrical path.

  • Negative return wire for each device should be as heavy as the positive wire: same current passes through each.

  • DC wiring near compasses should be twisted-pair to stop magnetic fields.

  • From Charles Kanter: DC wiring should have curlicues to give extra wire, reduce RFI, and reduce paths for lightning.

  • DC outlets inside cabin: use waterproof marine outlets instead of "cigarette lighter" outlets: more reliable.

  • Don't use household AC switches in marine DC circuits. The higher current and the DC nature of it will cause arcing when turning the switch off.

  • Put extra connectors in long runs of low-current DC wiring (navigation lights, etc) to make it easier to test, easier to pull mast, etc ?

AC wiring:
AC wiring (both standard and 3-phase) should be color-coded:
Wire Color (USA)Terminal ColorUse
Black or RedBrass or Gold or CopperHot
WhiteNickel or SilverNeutral
GreenGreenAC Ground
From Maurice Nunas on the IRBS live-aboard mailing list:
... Outside the US and Canada, and a few other US-satellite countries, there are only three wires, the wire colour changes, and the frequency changes to 50-Hertz. The safety ground is still GREEN (with or without tracer). The other ones can vary, but usually the neutral is blue and the hot is brown. There is no consistency in the plug style or how it is wired. I've found nearly everything! BE VERY CAREFUL! ...

From Lee Haefele on The Live-Aboard List:
I was horrified to find out that wire gauge vs capacity used in the USA (ie: 14 gauge is 15A, 12 GA is 20A, 10 GA is 30A), still gets very hot if the current is maintained long term. I have cable TV systems that are 24 X 7 operation at full current. My 20A circuits, running 15A actual, now have 10 GA wiring; outlets that accepted 10 GA wire had to be special-ordered. Keep the long-term current at about 60% of the wire "rating".
From Lew on The Live-Aboard List:
You are beginning to touch on why thermal magnetic circuit-breakers found in shore side panels are thermally derated by 20% as standard per NEC.

Using your example above, a 15A circuit-breaker is rated to handle 12A on a continuous basis. The 14 AWG wire insulation system protected by that 15A circuit-breaker is actually designed to handle 12A on a continuous basis.

It is one of the basic reasons that thermal-magnetic circuit-breakers are essentially worthless on board a vessel.

  • AC wire: BC5W2 or AWM or UL1426 best, MTW or HHW maybe.

  • AC wire: approximately, 14 gauge carries 15 amps, 12 gauge carries 20 amps. But you might have to derate for increased temperature.

  • All AC outlets should be 3-prong.

  • Most common AC wiring mistake: connecting AC neutral to DC ground.

From Ron Rogers on The Live-Aboard List:
I find bonding interesting. My Crealock 37 (1983 vintage) was not bonded and all thru-hulls continued to look like bronze (Groco). My 1973 Dyer 29 and my current 1985 Willard 40 are bonded. All thru-hulls have turned black.

From Kenneth McKelvie on The Live-Aboard List:
UK, and therefore I presume EU, standards do not permit bonding of thruhulls, for the reasons given in other replies and, I am told by the manufacturer of my boat, because every bonded item will be affected equally and therefore may fail at about the same time. At least if only one item is affected, you may spot that it is discolouring faster than the others and investigate.

From an article quoted in a message on BoaterEd forum:
Do not bond any thru-hulls or other immersed metal that can be electrically isolated. Specifically, keep your metal keel/ballast, your metal rudder shaft, your engine/prop, and all thru-hulls electrically isolated, from each other, and from the engine.

It's worth understanding the reason. In an increasing number of marinas, there are substantial DC electric currents running through the water. If your bits of immersed metal are bonded, the electric current will take the lower resistance path offered by your boat in preference to the water near your boat, and the current will flow into one of your bits of metal, through your bonding wires, and then out another bit of metal. The anodic bit of metal or thru-hull that has the misfortune to be on the "out current" side of the current running through your bonding system will also become "out metal" and will disappear, sometimes rapidly.

Your zinc is only intended to protect against the modest galvanic potentials and therefore currents that are caused by the dissimilar metals that are immersed and electrically connected together on your own boat. Your zinc is incapable of supplying enough galvanic potential to protect against substantial DC currents that may be flowing in the water. These DC currents in the water will cause electrolytic corrosion to your bonded thru-hulls or metal parts.

By using capacitors to block DC connections in a few key areas, it is possible to have perfect ground systems for AC, DC, RF, lightning, and corrosion, and have a boat that is immune to stray DC currents that are traveling through the water in "hot marinas".

In the old days, the technique of bonding everything together worked okay. In its defense, the "bond everything together" approach makes your boat less sensitive to electrolytic corrosion that can result from faulty wiring on your own boat. The problem is, the "bond everything" approach leaves your boat totally defenseless to wiring errors in nearby boats and nearby industry, that cause stray DC currents to run through the water.

Today the technique of bonding everything together would still work fine if your boat spent all of its time on the high seas, in remote anchorages, or in marinas that were wired perfectly and in which all of the nearby yachts were wired perfectly. Having underwater metal bonded together in crowded marina's today, however, is asking for expensive trouble. ...

Paraphrased from "The Boatowners Mechanical and Electrical Manual" by Nigel Calder:
  • Want 2-pole (hot and neutral) breakers on AC circuits.
  • Want voltage and frequency meters on AC main circuit.
  • Want GFI's on individual AC circuits instead of one central GFI.

Paraphrased from "This Old Boat" by Don Casey:
  • Voltage drop from battery to any point in DC wiring should be 3% or less. [Also, test drop from battery to back of radio when microphone is keyed on.]
  • Wire on a boat should always be multi-strand, not solid.
  • Use tinned wire for corrosion resistance.
  • Solder all connections.
  • Looping wire around a terminal screw is not as good as soldering a ring fitting onto the wire.
  • For on-deck 12-volt outlets: use Dri-Plugs.
  • Fuses are more reliable than breakers.
  • Follow ABYC color-code recommendations for wiring.

Fuses and circuit-breakers and GFCI's:
Fuses / circuit breakers are to protect wiring from overheating due to over-current, not to protect the batteries or the appliance being powered. So they should be current-sized according to the wire size.

Circuit-protection characteristics:
  • Current rating (typical max current; will open at 20% above this).
  • Opening speed.
  • Interrupt rating (current which can arc across open fuse/breaker).
  • Voltage rating (maximum operating voltage).
  • AC or DC (many fuses work with both).
  • Vapor-proof (ignition-protected) ?

Fuse types:
  • AGC == fast-acting.
  • MDL == time-delay (for motors with high start current).

SailNet - Chris Brignoli's "The Value of Circuit Breakers and Fuses"
Fuse / circuit breaker article by Kevin Jeffrey in issue 2002 #2 of DIY Boat Owner magazine

From Lew Hodgett on the IRBS live-aboard mailing list:
Re: Is there a difference between AC circuit breakers (household type) and DC circuit breakers?

There is a major difference between thermal-magnetic circuit-breaker's used in a load center or panel board (household type) for shore side building distribution systems and circuit-breakers, usually hydraulic, found on a boat.

The thermal-magnetic circuit-breaker found in your home is specifically designed to handle an AC load with no particular design attention given to DC service. If you check the DC rating, you will find it to be a small fraction of the AC rating.

A circuit-breaker designed for DC service requires a much more robust arc chute design than an AC circuit-breaker.

A circuit-breaker designed for DC service is not a thermal-magnetic device but rather a magnetic device.

For a given configuration and rating, the price differential between a thermal magnetic plug in circuit-breaker suitable for home service and a hydraulic circuit-breaker designed for DC marine service might be as much as 5:1.

Even the AC marine service circuit-breakers found on a boat, will have a price differential of at least 2:1 vs the household type.

There are many other major differences, but the above gives you an idea.

Bottom line ...

Leave the house circuit-breakers in the house. Trying to compare household circuit-breakers and marine circuit-breakers found on a boat is like trying to compare apples and oranges.

From Brian Woloshin on Cruising World message board:
... all DC circuit breakers sold for marine use have the same mounting dimensions.

Actually, these circuit breakers are only made by a couple of companies and are relabeled (and repriced) by the marine equipment resellers. They are not made specifically for marine use; their most common use is in industrial-grade electronics and computers.
From Leon Sisson on Cruising World message board:
I agree with Brian -- the mounting form factor seems to be fairly generic for a given current range. Before running out to order circuit breakers from the cheapest source you can find, be aware that they don't all have the same wiring terminals on the back. I like the ones with screw terminals, preferably with flat spade tabs in addition for wiring in pilot lights, circuit monitoring logic, etc. Some breakers have only the flat tabs, even up to 20A.

Somewhere around 50A the physical dimensions of the breakers seem to change. They'll still mount on the same side-by-side centers (3/4"?), but the "long" panel dimension gets longer, and they need more "depth" behind the panel.
From SG on Cruising World message board:
Occasionally, it's necessary to use a circuit breaker that is a "slow blow" type. Your peak initial motor load might cause a marginal sizing to keep tripping.

From Marce Schulz on The Live-Aboard List:
An arc-fault circuit-interrupter is a circuit breaker that performs like a regular one (tripping on overloads and short circuits) plus it contains an electronic chip that will detect arcing faults, which are so brief as to be undetectable by conventional breakers, and are apparently the cause of a large percentage of electrical fires. An AFCI is not the same as a GFCI, which only detects a leak to ground (as well as overloads and short circuits.) AFCIs have been around for a while and they've made their way into the National Electric Code.

... Arcing faults happen when wiring ages or deteriorates, and in the case of boats, planes, cars and motor homes, from corrosion and abrasion, etc. And an arc fault fire usually starts in some hidden area (where the wiring is) so they can really get started by the time they're detected by a smoke alarm. ...

From Procyon on Cruising World message board:
> Is there a difference between "marine" GFCI outlets
> and the ones at Home Depot for 1/4 of the price?

[General consensus seems to be "no".]

They range from about $4 for cheap to $22 for GF5362 industrial. A high quality for good price is a GF5252 for about $8. There is a difference in construction and components, the more money the more abuse it can take. The biggest difference though are the contact and construction of the ground bus. More expensive units have a one-piece ground rather then rivets to the mounting strap. Also a big difference on being able to handle constant high loads, like tools. A middle road like the GF5252 will resist corrosion and handle loads well above its 15 amp rating. It should never go bad so why pay more ?

From Pierre Mitham on the IRBS live-aboard mailing list:
... to make a good electrical connection you need to do the following to EACH connector that you use:
  1. Scrape the end of the connector where the crimp turns in to the lug.
  2. Slide a piece of adhesive lined heat shrink tube onto the wire to be crimped.
  3. Strip the wire 3/8" from the end.
  4. Slide on the crimp connector and crimp with the proper tool.
  5. Tip solder the end of the crimp to seal it (that's why we scraped the end of the crimp, to remove the oxidization). [Use rosin flux, not acid flux.]
  6. Heat shrink the tube over the crimp, leaving just the lug exposed.
  7. Add a drop of corrosion block to the lug before you attach it to the appliance/terminal strip.
From Steve on rec.boats.electronics newsgroup:
... It is important to bundle soldered connections so that they are supported on both sides. Vibration can break the wire at either end of the area soldered or affected by the heat of your soldering. Using heat shrink tubing over soldered joints adds to their strength also. Properly supported soldered joints don't come loose and don't have corrosion problems. ...

From Arild Jensen on The Live-Aboard List:
Welding cable is rubber-covered. Rubber disintegrates when exposed to oil, grease, ozone etc.

BTW Welding cable is considered a disposable product. Welders drag the cables all over the ground, splash it with molten metal droplets etc. Its a given that it has to be replaced every few month or a year, depending on abuse.

Welding cable is not tinned since it is not expected to remain in use long enough for corrosion to be a factor.

This is why surveyors fail welding cable for permanent marine installations.
From Norm on The Live-Aboard List:
The primary problem with welding wire is it's flexibility, which it gets by being constructed of many very fine wires just a few thousands of an inch in diameter.

When corrosion attacks the copper, the few thousands get eaten up quickly and you have no more copper.

Normal 1/0 wire, or even starter wire, had much bigger strands, so that a few thousands of an inch corrosion is still a small percentage of the strand, so it lasts much longer.

From Fred Terns on the SailNet liveaboard-list:
Whenever a "strange" 12 volt electrical problem is experienced, CLEAN THE BATTERY TERMINALS and CONNECTIONS. Even if you cleaned them just the day before, especially if you just cleaned them the day before. It costs nothing to perform this simple maintenance and it takes very little time.

Hand-held batteries:
From John / Truelove on the IRBS live-aboard mailing list:
I find that the NiCd batteries in my ICOM M1 and M1+ will not hold a full charge for long, especially in the heat of the tropics. They must be recharged every week or so, else the capacity is much reduced. ICOM says this is normal ...
From Jim / Ganesha on the IRBS live-aboard mailing list:
You might want to try and find equivalent batteries in Nickel Hydride, they are becoming fairly common now. A major advantage is they do not suffer from discharge memory.

Another thing we have done is have the handheld VHF that accepts alkaline batteries as well as the NiCd primary. We kept spare alkalines in the abandon ship bag.
From Mark Mech on the IRBS live-aboard mailing list:
Nicads lose 1% per day if they are in good shape. NiMh don't lose much and can be substituted for Nicads, but you need a good peak detection charger or you will fry them.
From Larry DeMers on the IRBS live-aboard mailing list:
Nickel Metal Hydride batteries would be a good replacement for those Nicad rechargeables. You will need a charger for them, but they will hang onto their charge for a very long time by comparison. As mentioned by another poster, they have no memory either, so they can be stored dead, and then recharged for use. For an emergency use only VHF, maybe Lithium Ion batteries would be even better. They have a shelf life of 10 years or better, before losing 10% of their capacity. ...

On-line stores:
Electronic Goldmine (discount, surplus, kits, etc)
Best Boat Wire and Cables

Proper disposal of old electronics and batteries:
Some manufacturers have recycling or disposal programs; check with your local computer or phone store.

See the Radio-Frequency Interference (RFI) section of my Radio On A Boat page

Electrical Corrosion

"I zinc, therefore I am."

  • Stray Current (often called "electrolysis", maybe inaccurately): corrosion caused by stray electrical currents seeking a ground.

  • Galvanic: corrosion caused by interaction of two dissimilar metals (forming a battery).

Anodes may be zinc, aluminum or magnesium, depending on where you boat, the hull material, and the type of metal in underwater fittings.

Don Casey's "Sacrificial Zincs"
BoatU.S.'s "Zincs"
Gene K. Wineland's "Combating Corrosion"
Yandina's "A Non Technical Education On Boat Electrolysis"
Jefa Rudder's "Electrolysis"
Metal Boat Quarterly's "Corrosion, Zincs and Bonding"
Robb Zuk's "Marine Electrical Check List"
Colin Foster's "Galvanic Isolator Explained" (and plans to build one)
"The Galvanic Isolator" article by Ed Sherman in 9/2000 issue of Cruising World magazine
"Corrosion Control" article by Sue Canfield in issue 2003 #2 of DIY Boat Owner magazine
Anodes article by Jan Mundy in issue 2003 #2 of DIY Boat Owner magazine

From Joe DeMers on Cal mailing list:
> Ground/bond what is the difference, I thought
> one was an adjective and the other a noun.

Nope - a common mistake. Ground wire is the electrical return conductor that completes the electrical circuit to the battery ground terminal. Bonding wires only connect metal masses aboard the boat. Bonding wires are designed to carry only very minimal current, and are not included in the boat's DC system (except where it's attached to the battery negative terminal). The bonding idea is to make all underwater metal at the same electrical potential, so no galvanic corrosion can take place.

Zinc (anode) locations:
Your boat may have many more zincs than you suspect; don't overlook:
  • Outboard motor.
  • Any heat-exchanger with salt-water flow: engine, genset, any water-cooled refrigerator, freezer or air-conditioner.
  • Any salt-water-injected exhaust elbow: engine, genset.
  • Gearbox.
  • Cam (insert that makes chamber non-circular) in engine raw water pump may be sacrificial.
  • Oil coolers.
  • Muffler.
  • Watermaker.
  • Head.
  • Any salt-water piping.
  • Keel.
  • Centerboard trunk.
  • Propeller and shaft (inside and/or outside hull).

Corrosion test kit (reference electrode / half-cell):
Kel Marine test set ($90)
Guest #2435 / West Marine 296584 ($70)?
Professional Mariner #20008 ($170) ?

From Brian Woloshin on Cruising World message board:
Checking for stray currents:

It is very possible one of your neighbors is the cause of the [rapidly disappearing zincs] problem. To check, get about a square foot plate of any decent conductor and a good digital multimeter. Hang the plate in the water on a wire and put the meter on AC. Compare the plate to the marina electrical ground. There should be no voltage difference.

Also compare between the plate and prop shaft and see if there is a difference there.

Nigel Calder in 9/2008 issue of Sail magazine:
"... stray current will corrode whatever metal discharges it back into the water, while galvanic corrosion will initially be concentrated at the zinc ..."

Zinc testing:
Use a sensitive voltmeter with a piece of pure silver on one probe.
Put the silver in the water, and the other probe on the metal being protected.
If < 500 mv, metal is underprotected.
If > 700 mv, too much zinc.
(This assumes fiberglass boat with bronze through-hulls.)

From "Corrosion Control" article by Sue Canfield in issue 2003 #2 of DIY Boat Owner magazine:
  • If a low-resistance electrical path is not maintained among parts and anodes, electrical corrosion can occur. Test for continuity (measure resistance) while boat is out of the water; can't do it in the water.

  • If the anodes provide too little voltage, bonding actually will promote electrical corrosion, by providing the path for current to flow.

  • Testing bonding performance (in-water):
    1. Disconnect all power sources (shore power, batteries, solar, wind generator).
    2. Dangle Ag/AgCl reference electrode over the side, more than a foot below the surface. Best if several feet from the parts being tested (but no closer). Connect to negative lead of multimeter.
    3. Measure voltage between each fitting and the reference electrode.
    4. All voltages should be the same. If not, bonding wires are faulty.
    5. Bonding system voltage should be at least 200 mV negative, relative to potential of least noble metal being protected. (Potential of bronze is around 300 mV.)
    6. If voltage is less than 200 mV relative, add more anode.
    7. Overprotection can create problems, especially for wood or aluminum boats.
    8. Reconnect batteries.
    9. Turn on DC circuits, one at a time, checking bonding system voltage (at any point) each time. If the voltage changes, that DC circuit is leaking stray current.
    10. Reconnect shore power. Wait a moment. Measure bonding system voltage (at any point). If the voltage has changed, stray current is flowing through shore power ground wire; install a galvanic isolator or isolation transformer.
    11. Turn on AC circuits, one at a time, checking bonding system voltage (at any point) each time. If the voltage changes, that AC circuit is leaking stray current. This is not a corrosion threat, but worse: it's a shock hazard.

Galvanic Isolator:
From Colin Foster on Cruising World message board:
The Galvanic Isolator explained.

The purpose is to disconnect your wet metal parts from the dock supply in order to prevent electrolysis. The trouble is, however, you need them connected together so that if there is an electrical short on the boat, it doesn't make the boat alive at 120 volts or worse - gives you quite a kick when you step off an aluminum dock!!

The galvanic isolator relies on the fact that electrolysis voltages are quite low - usually less than one volt - whereas electrical failure voltages are quite high. Silicon diodes, which are used to conduct electricity in one direction but block it in the reverse direction, have a built-in forward voltage drop of about 0.6 volts. It is not like a resistor voltage drop - no current has to flow to create the drop - so below 0.6 volts it is disconnected, above this it conducts with very little resistance to current flow.

Since we don't know the polarity of the fault voltage, and if it is an AC fault, it will be flowing both ways, two diodes are placed in parallel pointing opposite directions so there is always one available to conduct, but at low voltages, both are switched off and no electrolytic current can flow.

Since some electrolytic voltages are higher than 0.6 volts, a good galvanic isolator should have two diodes in series in each direction to give a 1.2 volt isolation. Some also add a capacitor to increase the ability to conduct AC current, however I personally think this is a mistake as it does allow low level AC currents to flow and cause electrolytic type activity, even if not true electrolysis.

The diodes have to have enough capacity to pop a shore power circuit breaker if there is a short on your boat. This can require a capacity of more than 100 amps. Galvanic isolator diodes are designed to carry this current for a very short time - long enough to blow the circuit breaker plus a safety margin - but they cannot carry it for very long without overheating.


There are two ways for a galvanic isolator to fail: either the diodes are shorted, or they are blown open. You can test them with a digital voltmeter that can read positive and negative voltages. At any time, with the voltmeter on the DC range, put it across the shore power side to the boat side. There should always be some residual electrolytic voltage (unless you are hauled out) so the meter should read something less than one volt. If it always reads zero, the diodes are shorted out. If it reads greater than about 1.2 volts then the diodes are open circuit. Switch to AC volts and check again since if AC is flowing, the DC meter setting may not show any activity.

From Colin Foster on The Live-Aboard List, 7/2002:
West Marine are coming out with a new galvanic isolator. It is only 4"x4"x1.5", suitable for up to 50 amp shore power or 2 X 30 amp shore power, fully waterproof, and the discount retail is expected to be about $100. It meets all ABYC specifications except it does not come with a built in remote indicator panel. You can download the draft copy of the owner's manual from http://www.yandina.com/manuals.htm and click on Galvanic Isolator. There are also instructions on how to build your own for less than $20 at http://www.yandina.com/galvanicIsolator.htm

FYI, I am not a disinterested party, I manufacture the West Marine brand galvanic isolators.

Want an isolator with a capacitor inside, so a diode failure does not break the ground connection.

Mercury Marine Quickilver Galvanic Isolator kit (part 18478a3).

Isolation Transformer:
From Arild Jensen on The Live-Aboard List:
> what size I should get ?

Transformers are not rated in amps or watts, but in kilovolt amps or KVA for shorthand.

30 amp 120 V service requires a 6 kW isolation transformer.

50 amp service requires a 12 kVA isolation transformer.

Be aware that there are two types of 50 Amp services. You can get a 3-wire 50 amp which is strictly 120 V, or a 4-wire 50 Amp service which gets you 120/240 V.

When you have a 4-wire 50 Amp shore power service, it's normal practice to just connect the two hot lines L1 and L2 for a straight 220 V service. The isolation transformer has a center-tapped winding on the output side to give you the 120 V. The center tap becomes your neutral for the 120 V and it is grounded.

You should also be aware that there is a big difference between a real marine isolation transformer and a polarization transformer. The latter does not confer real isolation to the boat, nor does it have all the other little details such as a shield between the windings.

GPS (Global Positioning System)

Bad ways people use GPS:
Some suspect that more boats are lost now than before the advent of GPS:
  • Too many sailors assume that auto-pilot and GPS are infallible, and that they don't have to keep a good watch.

  • Often the GPS and chart coordinates (datums) are different by miles, or the chart is wrong (even latest electronic charts).

  • GPS doesn't prevent collisions, especially with someone using the same waypoints but on a reciprocal course.

  • GPS may tempt people to sail in low-visibility conditions.

  • GPS can be far less accurate when fewer satellites are visible, or they are bunched in one part of the sky (especially outside USA, and in high latitudes).

  • It is easy to fool yourself into believing the push-button, precise answer from the GPS instead of the evidence right before your eyes (breakers, water color change, etc).

  • A single wrong digit programmed into the GPS or read from it can be hard to notice and have large effects.

  • GPS can display positions in different modes (i.e. degrees/minutes/seconds or degrees/minutes/decimal) with four modes possible and any difference in mode will leave you off. Miles off.

  • When you program a waypoint into the GPS, is it a safe place to sail, or an obstacle to avoid ? Will you remember which type it is a day or two later ?

Also, GPS leads people to point the boat directly toward the next waypoint, without considering that currents or winds might make it more efficient to sail a different course.

From "The Voyager's Handbook" by Beth Leonard:
Almost all of the boats that were lost during the course of our circumnavigation were lost closing with land at night. Some were trying to enter reef passes in the dark - something they never would have considered had they not had a GPS aboard.

From Gary Elder:
There seems to be a trend now to market GPS chart plotters and let the older, more basic GPS's go away. Chart plotters are wonderful toys, but some people think they can be dangerous because they don't require any piloting or navigation skills to use. Also, the nav charts contained in those great little boxes are frequently not current. I have seen many people purchase chart plotters BECAUSE they can make whatever passage they want without ever having to learn anything about navigation. Some experienced navigators/cruisers feel that chart plotters 'breed complacency' which can lead to trouble.

From Dennis Biby on The Live-Aboard List:
[Re: using waypoints from web sites and cruising guides:]
... why would anyone use someone else's waypoints? Maybe for fishing holes, wreck diving, or ?, but I don't see their value for navigation. Even if they are offered for an area where the channel wanders around, it seems they would only be of value if you knew when they were created and by whom and then decided to place your safety in their hands. ...

SailNet - Bill Biewenga's "The Importance of DR"

My instinct is to use GPS for 2 things only:
1- What is current position (lat/long) ?
2- What is current Speed Over Ground ?

BoatSafe's "GPS Overview"
West Marine's "Selecting a GPS Receiver"
How Stuff Works' "How a GPS Receiver Works"
GPS's reviewed in 4/1/2000 issue of Practical Sailor.
Peter Bennett's "NMEA FAQ"
Joe Mehaffey and Jack Yeazel's "GPS Information"

GPS / Chart Discrepancies,
summarized from letter from Steve Salmon and Tina Olton in 6/2000 issue of Seven Seas Cruising Association bulletin:
  • GPS and chart may have different datums (formulas for shape of Earth).
    All GPS's use WGS84 datum.
    • If chart uses WGS84, no conversion needed.
    • For some chart datums, some GPS's will do conversion for you.
    • Some charts have legend telling how to convert chart coordinates to WGS84.
    • If chart datum unspecified or unknown to GPS, use compass bearings to get fix on chart, read GPS, and calculate GPS-to-chart conversion for that chart.

  • Chart may be wrong; be skeptical, be careful, sail with your eyes open.

From Eric Thompson on The Live-Aboard List:
NMEA 0183 uses 2 wires in each direction, i.e. is differential. This makes for a VERY noise-resistant communication if the interface is installed correctly. When I was working for Trimble Navigation part of my job was to test our units interfaced with as many other units as possible. The permutations are amazing. Furuno thinks it is a current loop system so you need a resistor to ground to develop voltage so the listener can "hear" it. Many manufacturers have the + and - signals reversed. Those who wrote the "Standard" (I've read it) did their level best to make it as confusing as they could.


Standard NMEA 0183 is 4800 baud, 8 data bits, 1 stop bit, no parity. Data out from your laptop serial port should be connected to "Input -" on the Furuno. Then try a 1000 ohm resistor to ground from the "Input +" pin. (Furuno thinks NMEA is a "current loop" type signal). THEN make sure the radar and the laptop SHARE the same ground (the serial port on the laptop and the i/o port on the radar both should have a separate 'ground' pin connected together).

If this does not work you may need to buy a "RS422" i/o card for your laptop. The NMEA IS rs-422!

From Mike Cox 2/2012:
Most GPS antenna's are compatible. The most important thing is the voltage to the antenna. The newer series going back about 5-8 years all use 5V; the very old series use 12V. I think you said you have a Garmin GPS - should be 5V.

From Xavier 2/2012:
Garmin and most other manufactures for that matter have 3 different types of GPS antennas:

1. The plug on the end is BNC only has a center pin and uses coax for the wire. Resistance on this type of antenna should measure about 50 ohms if good.

2. 0183 smart antennas. These usually have 7 pins. They work off the NMEA 0183 standard. If you cut the plug off you will find individual wires. Red goes to 12 VDC, black goes to negative, yellow to accessory on, blue is data in which gets connected to data out on your GPS, white is data out which gets connected to data in on your GPS.

3. N2k smart antenna. This antenna does not have a cable. It has a plug on the bottom of the antenna. This will work only with newer systems that accept NMEA 2000.

GPS can be jammed fairly easily, since the signals coming down from the satellites are very low-power.

Lightning Protection

Lightning striking tree

There are two things that cause damage: the direct path of the lightning strike, and the electric fields produced by it. The direct strike is capable of destroying just about anything; the best you can do is give it a straight, highly conductive, relatively harmless path to ground. The electric fields can induce destructive currents in wiring and circuits, blowing them out; you can protect against these by disconnecting things in advance, installing surge suppressors, and putting some items in metal boxes.

SailNet - Don Casey's "Lightning Precautions"
William J. Becker's "Boating-Lightning Protection"
Bill Laudeman's "Understanding Lightning Protection"
SailNet - Kathy Barron's "Lightning Strike!"
SailNet - Kathy Barron's "The Path to Lightning Protection"
Lightning protection article by Susan Canfield in issue 2002 #1 of DIY Boat Owner magazine
West Marine's "Lightning Protection"
Article by Alastair Buchan in 12/2001 issue of Cruising World magazine
Earl Hinz's "Lightning Protection for Multihulls"
Ewen M. Thomson's "Lightning and Boats"
Metal Boat Quarterly's "Corrosion, Zincs and Bonding"
Florida Live Lightning Tracker

Comm-Omni International lightning and transient surge protection

Attaching a copper grounding strap to the bottom of an aluminum mast:
separate them with stainless steel, and clean the connection annually.

Paraphrased from "The Boatowners Mechanical and Electrical Manual" by Nigel Calder:
  • GE MOV V36ZA80 Metal Oxide Varistors across DC power leads to equipment.

  • When in lightning danger, disconnect from shore power.

  • Lightning strike nearby may affect compass deviation.

From Will on Cruising World message board (not about lightning):
Buy a bunch of MOVs and protect all your circuits, don't forget to add a series diode in the positive lead that's if your equipment can handle the voltage drop. MOVs have no impact on voltage or circuit operation. You can pick MOVs up from Radio Shack etc, 2 dollars each. Make sure you buy one that has at least 5 volts above your max operating voltage.

From Ken, Jackie and Daniel on the WorldCruising mailing list:
... Please DO NOT use MOV's on your 12 volt electrical system. These are used in AC electrical systems to 'absorb' surges caused by lightning strikes. There also are versions that work on 12 volt systems. They are cheap and very dangerous. While they WILL absorb some of the high voltage spikes they WILL stop working without warning leaving your gear completely vulnerable while you think it's being protected. But that's not the real problem. When MOV's are exposed to sustained overvoltages (as occurs in charging system / battery charger failures) they have a tendency to BURST INTO FLAMES. One of our friends in Australia almost lost their boat to fire due to one of these cheap MOV's. The damage was considerable. The STO-P protector I mentioned does not use these. It's more expensive but delivers the goods in complete safety. ...

From John / Truelove on IRBS live-aboard mailing list:
IMHO, one of the worst things to do is to bond thru-hulls, pulpits, etc. together and thus offer lightning a guided tour throughout your boat.

We have a single 4/0 copper wire from the step to an oversize bolt on a big dynaplate directly below the mast. One inch copper straps run from the chainplates directly to this same connection. This was done by the OO, and (hope I'm not tempting fate!) in 20 years of cruising the Bahamas, Caribbean, or docked in Cape Canaveral, never a strike. I'm not about to change anything.

Further, I don't think it's a good idea to hide below during a thunderstorm if underway, leaving the helm unattended, unless you are at sea and have RADAR. The chances of running into another boat (or dragging in an anchorage) are much greater than your chances of being hit by lightning. Three years ago I spent a very scary half-hour in the cockpit keeping the boat (under power *and* anchored) - away from all the other dragging boats in the Wrightsville Beach anchorage - the worst thunderstorm I've seen in my 50+ years. I certainly wasn't thrilled to be outside, but if I hadn't been, we would have been on the beach with the others who stayed below.

From Lew Hodgett on The Live-Aboard List:
Introducing lightning into a discussion about bonding is like trying to have a discussion about oranges and apples.

As far as lightning protection bonding is concerned, I'm from the school that considers it a complete waste of time and money.

Very little is known about lightning except that it doesn't like to change direction.

That fact renders almost any attempt to provide bonding protection on a vessel as less than useless, IMHO.

Grounding plate should be solid bronze, not a sintered bronze Dynaplate (which are porous and can explode when lightning passes through).

From Bruce Clark on Cruising World message board:
A number of years ago I had the 'interesting' experience of being hit by lightning (the boat, not me) on a passage to Bermuda in a Nonsuch 30. I was on watch (22:00) when we were hit and saw the Windex falling downward in a semi-liquid state. At the time there was probably half an inch of water in the cockpit from the intense rain but I did not feel anything. The strike blew out all of the nav lights except one and fried the voltage regulator -- other than that, no damage. The boat had a grounding strap from the masthead to keel. On the Nonsuch this involves a 90 degree bend with the cable travelling horizontally about 10 feet. Also, there is no standing rigging.

The remarkable thing about the experience was that we were hit only once and only after about 2 hours of the most remarkable lightning display I could ever imagine. Lightning frequently hit the water quite close to us and there were hundreds of strikes with no appreciable delay between the lightning and the thunder. What I took from this is that it is harder to get hit than it might appear at first glance. What we did during the strike was sit in awe of what was happening -- it was totally incredible. I seem to remember one of the crew saying something about not leaving a full bottle of single malt scotch if he was going to die -- he took it to bed with him when he went off watch.

In the area where I sail (Lake Ontario) there are forecasts of the possibility of thunderstorms on at least half the days in the summer. If I only went out in nice weather my sailing would be much restricted. I think the chances of me being killed by lightning are a lot less than those of being killed driving to the yacht club.

From Will on Cruising World message board:
I got hit in Fjord Land New Zealand and despite all the measures I lost every piece of electronic equipment, including the alernator and all pumps. I also lost my windlass. This was on a steel boat. My backstay insulators looked like swiss cheese. What I found amazing was the numerous puncture holes around the prop shaft, I initially thought it was the stern gland leaking. When I hauled out and checked everything I found these nice clean puncture holes about 2 mm that had punctured 5mm steel. I was not on the boat when it occurred, I doubt if any measures could have been taken to prevent this level of disaster. I thank my lucky stars that I was not on board. When you're dealing with mega joules of energy I don't think there are hard and fast rules that apply across the board. I would add that there are companies like PolyPhase who make numerous devices that protect electronic equipment that make claim to withstand multiple direct hits. The broadcast industry seems to rely on these devices, but as we all know now and again these do fail.

From Dave Gibson on Cruising World message board:
... The generally accepted theory (at our club anyway) is that grounding attracts lightning, so you should either be grounded right, or not at all. Factory grounding is too light and can't dissipate a lightning charge, holing the boat ... [He disconnected his factory-installed grounding wires.]

... Whenever we're on the boat and there is a threat of a storm, I attach automobile booster cables to my backstay and drop the other end in the lake, hoping that lightning will take the shortest path from the top of my mast to the water. ...

From Jeff Eaton on the SailNet's Gulfstar mailing list:
Lightning is so capricious that there is no guarantee that whatever you do will be the right thing. A local rigger here in Ft. Lauderdale has sold every commercial lightning device available, and every one has been hit. His very tongue-in-cheek suggestion is that the best idea might be a large green garbage pail over the top of the mast. Seriously, the best thing is to find what makes you the most comfortable, perhaps with some input from your insurance company, and go with it. Good luck!

From Gary Elder on the Morgan mailing list:
Lightning is certainly strange stuff. No two strikes ever seem to be the same. I've been lucky, only one minor one to deal with, but I have been privileged to talk to many people who have really been 'nailed'.

Each of them had a similar story to tell ... Some (spell that most) insurance companies will try to get you to settle your claim too early. Finding major electrical/electronic damage is easy, but you may still be finding damage to basic electrical circuits six or eight months later. Have all the inspections done, be careful with what you sign, and go slow.

From DarthZ on the Morgan mailing list:
I have had my boat hit three times in four years here at Indian Shores. It is strange, motors will work one day and literally fail the next day. I have had pumps that were less than 9 months old that were working after the strike only to fail three months after I got my boat back from repair. If in doubt replace an item; it will fail when you need it the most. Be sure and check the bottom of the keel for small holes.

From Ron Rogers on The Live-Aboard List:
I had a lightning strike 30 yards off my starboard bow while in a slip and connected to shore power. Things were damaged that did not appear to be damaged. Things that were factory repaired failed within a year.

A buddy had access to an electron microscope and examined my RG8U, mil spec, Belden antenna cable. At that magnification, the interior insulation was fused in a multitude of places. This was done in comparison with a new piece of Belden cable.

All my electronic/electrical gear had to be replaced. Many electronics firms like NorthStar and Datamarine refused to attempt a factory repair after looking at the equipment. They declared the equipment to be a total loss. ICOM did repairs which failed within the year.

From Ed on "Angel Louise":
[Catamaran hit by lightning 6/2010 in Melbourne FL, with about $16K of damage.]

We have a grounding plate, wired all through-hulls together, lightning rod and cable from mast. We think it came through the water from a strike of the ICW near us.


We weren't directly hit on our mast by a lightning bolt, but it struck the water right next to us. Or as our friend Lester Forbes calls it: a "sideswipe". If lightning hits the mast - you'll likely get some crispy instruments aloft, like fried wind indicators and fried antennas. We did not have that. But we did have a bunch of electronic$ aboard that got toasted as the electrons and extremely high voltage took a path into the boat and actually burned holes in circuit boards and charred components in various electronics. We were originally not going to report it to our Dutch marine insurance company, as we have $3K deductible insurance, but finally decided to do so when we saw an estimate was pegged around $16K.

Both of our original $4,700 list price chart-plotter / radar displays (in inside and outside steering stations), the $1800 Radar antenna on the mast, network elements that wired it all together and controlled them and the autopilot commands, and two expensive instruments hooked to the autopilot, all turned belly-up and died. We also had two Engine Hobbs meters hit. And hope it is nothing worse.

Putting equipment in a metal "Faraday cage" to shield it from lightning:
supposedly aluminum foil is not thick enough, and the cage should be grounded.

Lights      Lightbulb

Interior lights:
  • Incandescent (screw-base, or car-type):
    Easily available.
    Least efficient (10 lumens/watt).

  • Halogen incandescent:
    More light but more heat, gives off some UV, damaged by overvoltage.
    Small and fairly cheap.
    A little more efficient (14 lumens/watt).

  • Xenon incandescent:
    20 percent less efficient than a halogen, but superior in every other way.

  • Fluorescent: large-area lighting.
    More light over large area with less heat and power than any other type.
    Starting takes a lot of energy and decreases bulb life.
    Electronic-ballast is better: has surge protection, can be dimmed, doesn't emit RFI, prolongs bulb life, reduces flicker.
    Very efficient (50+ lumens/watt).
    Can't be dimmed.
    "Warm-white" or "full-spectrum" gives nicer light, "cool-white" is slightly more efficient.

  • Compact fluorescent.
    Do web search for "12V fluorescent screw-in bulbs" to get replacements for incandescent bulbs.
    Home Depot sells a 12V "EcoBulb".

  • Cold-cathode fluorescent:
    Most efficient (80 lumens/watt).
    Can be dimmed.
    Superior to normal fluorescent in every way except cost.

  • LED:
    Very efficient, run cool, but not much light output, and high cost (but they're improving).
    From 9/2004 issue of Practical Sailor:
    "LEDS achieve their brightness by a combination of factors, but two of the biggest factors are the reflector that the LED chip sits in and the lens above the chip. To achieve its high brightness, the LED light spread is very narrow comapred to other lamp types."

  • Oil:
    More light than incandescent.
    Need gimbals, maybe soot-hood.

  • Propane camping lamp for use in cockpit ?
    Cheap, but will boat motion affect it ?

  • Kerosene lamp with citronella oil for use in cockpit ?

Color Temperatures:
  • 1800K: candle flame.
  • 2000K: sunlight at dawn or dusk.
  • 2700-2800K: 100-watt tungsten-incandescent lamp.
  • 3000K: typical 12 VDC halogen bulb.
  • 3000-3300K: standard "warm white" fluorescent.
  • 5000-6000K: direct sunlight at noon.

LED replacement for halogen reading light:
From Lee Church:
For LED replacement for halogen reading light, I would recommend a couple of things:
  • Get a warm rather than cool spectrum light. I got the cool white, and it looks too much like a fluorescent light. The warm light might be better for reading anyway; less glare from the white pages.
  • Get a light that can handle up to 15 VDC. The ones that only go up to 14 volts are great if you have a regulator on them, but you won't have one, so when you charge your batteries you may well go over 14 V (I should hope you do when you charge!). The lights that handle up to 15 V may actually not be as bright but they have less chance of you ending their life early.
  • I think a recessed light with a glass/plastic lens is a great idea. Though the ones with the LEDs sticking out give more light per milliamp, I think I would rather have one that looks more like a light. It also will mean when you look at it from the side you won't have the glare that I get when the LEDs stick out of the socket a bit.
  • While I got a 32 LED MR16, I found the 12 LED MR11 (smaller bulb) produces enough light to read by as well, it's really the color/temperature that annoys me (the cool white). So, a 24 LED MR16 should be fine for reading.

Bottom line? A warm temperature/color 24 LED higher maximum voltage (15 V?) light in a lens-covered MR16 socket is what I would give a shot at.

MR16 / GX5.3 / GU10 base: two pins 5.2 mm apart.
MR11 / G-4 base: two pins 4 mm apart.
For $2, can buy a ceramic socket to change your fixture from one to another, or to a "universal" socket (for example, Super Bright LEDs socket).

Instead of buying expensive 15-volt-tolerant LEDs, buy cheaper 12-volt-only LED and put a current-limiting resistor in series with it. The resistance needed is R = Vdrop / I. For example, to run a 12-volt LED when batteries are at 14 volts, you need Vdrop = 2 volts. If the LED draws 80 milliamps of current (I), then R = 2 / .080 = 25 Ohms resistor needed.

Good (but expensive) warm-white 11-15 VDC LED bulbs: Doctor LED (but site only takes PayPal).

My experience:
I wanted to replace a halogen bulb in a reading light that's in my berth. The fixture is a foot from my head as I lie in bed reading.

In 1/2007, I bought a 12V 15-LED warm-white bulb from EBay store LEDBulb.bizz for $5.40 plus $4 shipping. The box says the bulb is a "LEDlamp Ultra Bright MR 11 12V AC/DC". The bulb manufacturer trademark is "PC" with a picture of a flying bird in the middle. Or "POC" with the bird inside the "O".

Since it's a 12V bulb, not a 10-15V bulb, I use it only at night when the battery voltage is down below 12.7V or so. I didn't put a current-limiting resistor in series with it.

The color is a little "cooler" than an incandescent, but works fine for me.

The light is more focused than I expected; adding a lens might fix that. A lens might dim it a little, so a 24-LED bulb might be needed.

The bulb generates zero heat and uses less power than my battery monitor can measure, so I'm very happy with it.

In 1/2007, the few 12V LED-bulb vendors all seem to be small operations with various quirks in their web-stores. Often it is hard to figure out what type of base their bulbs have, or how to specify color when ordering. Most only accept PayPal; some won't ship to PO boxes or outside USA. Some have punitive shipping costs or surcharges for small orders.

LED replacement for wide-area cabin overhead light:
From Lee Church:
LED lighting for area lighting is tricky business, particularly if you are trying to out-perform fluorescent. Because LEDs are so directional, they are hard to use for room lighting, as they create a lot of shadows. One large light will be like having a spotlight in your cabin ...

... I found a bunch of Seasense 8-LED lights at Walmart for $1 apiece ($1 for each 8-LED light assembly). [Modified them and] mounted 6 of them in the main cabin; to shield the eye from the direct light I mounted them behind the handholds on the cabin ceiling ... In total I have 48 LEDs in the main cabin which draw roughly 475 milliamps (depending on supply voltage of course). This lighting doesn't provide as much light as the fluorescent (7W two-bulb over sink), but is in between accent lighting and cabin lighting. ... [The main cabin light still is a 15W incandescent fixture.] ... For cabin lighting that would not require additional lights, my 7 x 8 settee area could use a total of 96 LEDs rather than the 48 I have in place.

From Sam Densler on The Live-Aboard List 4/2007:
Tried the 40-LED bars that intend to replace the fluorescents and was disappointed. I replaced all of the other lights in the boat with LEDs but the fluorescents stay until someone designs an LED set that can broadcast light like the fluorescent.

My experience:
In 12/2008, I bought a 12V 38-LED white bulb with normal screw-in base ($17 for 2, including shipping, from goldenpsx on EBay), to replace a 25W incandescent in my main cabin.

The 38-LED bulb is not as bright as the 25W bulb it replaced. Maybe a 60-LED bulb would be as bright.

SailNet - Tom Wood's "Proper Cabin Lighting"
Article by David Brady in 4/2003 issue of Cruising World magazine
Mo Girard's "Light Up Your Life!"

Alpenglow (fluorescent) is good (low power consumption). Hand-made by Bob Stoeckley, PO Box 415, Eureka MT 59917, 406-889-3586.

Fluorescent lights make DGPS receiver stop working, affect marine SSB and Ham radio, affect depth-sounder ?

Kerosene lamps are too hot for belowdecks in hot climates, too unreliable abovedecks.

From SailNet - Sue and Larry:
  • Use white or light fabric on cushions. (Leather or ultra-leather coverings don't stain like cloth. We had ultra-leather on Safari, and loved it.)
  • A large mirror on the bulkhead will reflect light wonderfully back into the cabin. If you can strategically place one or more of your lights near the mirror, you will get the greatest benefit.
  • Many people change the area around the ports on the inside of the cabin-house to white. You'll be amazed at the difference in brightness.
  • High gloss varnish will reflect more light than a satin or oiled finish. If you don't want to go full-bore with the gloss, try using it on the trim pieces only. This often provides a nice effect without being too glossy.

From Rick Kennerly on The Live-Aboard List:
... install small round or rectangular mirrors on the bulkhead behind all lamps. This nearly doubles the light they give out.

From Chris McKesson:
The halogen lights that have been recommended by others are also what we have come to use. Our breakthrough, though, has been to find a source with greater variety of styles at about half the price ...

I find that stores such as IKEA (my preference) and sometimes Home Depot both sell a wide range of lighting units which use the two-pin 10W or 20W 12V bulbs. These units have 110VAC-to-12VDC converters included somewhere: A couple that we have used have the converters in the power cord, in the form of a wall dongle that the homeowner plugs in. In other cases we have used some nice gooseneck type desk units which have the converter embedded in the base of the unit.

For use on the boat all you have to do is snip out and throw away the converter, and wire directly to the 12V side of the equation.

We have found under-counter lights (which we used in the galley) for $12 a pair (with bulbs) and the gooseneck desk lamps (with bulb) for about $10 each. Replacement bulbs at IKEA are $2.50, versus as much as $20 in a marine store.

From article by Nigel Calder in Feb/Mar 2004 issue of Professional BoatBuilder magazine:
  • Incandescent and halogen bulbs suffer greatly from over-voltage; running them while battery-charging at 14.4 V might cut their lifetime to 20% of the rated lifetime. Many larger yachts use a DC-to-DC converter to give a stable 12 volts for the lighting circuits.

  • All "DC" fluorescents contain an inverter that produces AC (and also RFI).

  • No difference between tubes for "AC" and "DC" fixtures. Any tube of correct wattage, size, and pins will work.

  • As soon as fluorescent tube starts to act up (slow to come on, flicker, purple flash when starting, ends of tube blackened), replace it. This helps to protect the ballast. In dual-tube unit, both tubes should be replaced at same time.

  • Larger-diameter 15-watt fluorescent tubes are more efficient and durable than the 13-watt tubes commonly used on boats.

  • Fluorescent tubes should have high humidity rating, often stamped "HH".

  • Most common fluorescent fixtures are from Thin-Lite, but those from Frensch (Imtra) and Alpenglow are better. Frensch Resolux are very good.

Exterior lights:
Navigation lights:
SailNet - Tom Wood's "The Davis Mega-Light"
Navigation lights tested in 1/15/2002 issue of Practical Sailor.

From Jim / Ganesha on the IRBS live-aboard mailing list:
When we pulled the mast on Ganesha last year we added a Davis Mega-Light ... only draws .074 amps per hour and is auto on/off. (Actually they are not LED but a very small incandescent bulb, looks like what we used to refer to as "grain of wheat" bulb used in scenery on model railroads. I believe a bulb like this when used with very low current has an extremely long life.)

I highly recommend it , but with some caveats.

It is not very bright - claims by the manufacturer aside; however it is much better than nothing. It does draw next to nothing with regards to power consumption.

Because of the these factors we also installed a new tricolor/anchor/strobe from Aqua Signal at the masthead. If we are in a heavy-traffic area where we really feel the need to make our presence known, we use the main anchor light, or where the small light could be easily "lost" such as in anchorages where there are a fair number of lights on the shore. In "deserted" anchorages we use just the small Davis light. We also use the Davis light when we go ashore during the day. That way we know at least some anchor light will come on when it gets dark and we haven't gotten back to the boat.

From Rick Kennerly on IRBS live-aboard mailing list:
There is a company turning out a white LED cluster anchor light that is USCG approved, uses almost no energy and has photo cell to turn the light on and off.

On a related issue, a couple of people were concerned about the brightness (or lack thereof) the Davis unit, one even replacing the bulb with a higher power wattage.

I'm actually less concerned about that. Actually, for years I've set two anchor lights, one is the built-in one at the masthead and the other a Guest marker light that I hang in the foretriangle just 4 foot off the deck.

The one up waving at the stars is well out of the field of vision of someone zipping around the anchorage in a dinghy. So, its brightness isn't all that critical. That's the reason I hang the second one -- in hopes that it will catch the eye of some half-looped dinghy jockey trying to find his boat.

I also have the boat name as 2" letters in reflective red and green forward with white patches aft, so anyone with a flashlight sweeping the area ahead of them will get a cue that we're there.

My experience with the Davis Mega-Light Masthead 3310:
The instructions don't tell you which bulb is which ! 1893 is the "bright" bulb; 1892 is the "energy-efficient" bulb.

The packaging is deceptive: they never say whether it is an approved anchor light; they call it a "masthead" light. They told me: both bulbs are 2 NM visibility, but one or both doesn't meet the candlepower requirement, so the light is unapproved. I installed it as an anchor light anyway.

Over the next several years, I went through four of these fixtures; the photo-cell circuit keeps dying ! Heard from at least one other boat that's had similar problems with them. Don't buy them; they're crap.

After climbing the mast a dozen or more times to fix the anchor light, I've decided to remove it entirely from the mast and put it down lower (hanging from the boom, or on top of the pilothouse).

LED lights (navigation and interior):
Deep Creek Design (web site is gone)
Orca Green

All of the major marine stores are starting to carry LED lights of some form.

From Ken James on The Live-Aboard List:
> LED running lights from Defender for under $50 each.

That sounds like the Perko sidelights. They are reasonably well designed, but you must mount them in the correct place on your boat (they cannot be mounted just 'anywhere' or you get too much sector bleed over) and they use a linear regulator to supply power to the LEDs, a not very efficient approach.

LED lights (exterior non-navigation, and interior):

Cold-cathode dimmable fluorescents from Taylorbrite
Sarana's "Cold Cathode Fluorescent Lamps"

6/2009: USCG issued alert that Compact Fluorescent Lights (CFL) may interfere with certain communications equipment.

From Marilyn Morgan on IRBS live-aboard mailing list:
... LEDs don't burn out as such, like traditional incandescent lamps do, but they do lose brightness and/or shift in color over the course of their lives. So at the end of however many hours of life the manufacturer predicts, your light may still be burning, but it may be too dim or too off-color to serve its purpose. You may want to ask the manufacturer whether they have accounted for loss of brightness and/or color-shift in their life predictions. ...

From Sarana's "Cool Stuff":
If you are looking for LEDs to use on your boat, buy the brightest ones you can find, 1500 mcd to 6000+ mcd. ... Don't waste your time with any LED's that are less than 1500 mcd. Be careful because manufacturers play with the specs by narrowing the "visible cone" to increase the mcd rating. So look for something with at least a 20-degree cone (or larger) and 1500 mcd or more.

Big LED flashlights: some quick searching on the web 12/2006 showed me that many of the prices advertised are deceptive. The prices are for flashlight only; the battery and charger are extra.

LED spotlight/floodlight: LED Mega Beam, $200 from Hella Marine, draws just 7 watts.


  • Power.
  • Range.
  • Resolution / horizontal beam angle (smaller angle is better).
  • Vertical beam angle (bigger angle compensates for heeling better).
  • Screen type: CRT or LCD.
  • Screen size (pixels).
  • Screen night-viewing mode: brightness control, or color-change (better).
  • Periodic scan (watch/sleep) mode ? Guard zone and alarm ?
  • Mount: fixed, gimballed (automatically leveling), or manually leveled.
  • Navigation data input ?

As of 1/2009, "HD RADAR" (murky definition, but generally DSP-based) is available, and solid-state / non-magnetron scanners are coming.

BoatU.S.'s "About RADAR"
SailNet - Jim Sexton's "RADAR Basics"
West Marine's "How to Select a RADAR"
SailNet - Liza Copeland's "The Wonders of Radar"
"Multiple Targets" article by Dryw Lloyd in 1/2001 issue of Blue Water Sailing magazine.
RADAR article by Larry Douglas in issue 2000 #3 of DIY Boat Owner magazine.
See low-power LCD RADAR reviews in Practical Sailor's 1999 Gear-Buying Guide.
RADARs tested in 11/1/2000 issue of Practical Sailor
Entry-Level LCD RADARs tested in 9/2004 issue of Practical Sailor
Four low-end RADARs tested in "Compact RADAR" article by Ed Sherman in 10/2001 issue of Cruising World magazine
HD RADAR article by Ben Ellison in 9/2008 issue of Sail magazine.

From Brian Woloshin on Cruising World message board:
I have a 4kw CRT RADAR mast mounted about 25 feet high. It does not have a leveling mount. I find that on rare occasions I lose a scan or two due to rolling or pitching - not enough to convince me I need a leveling mount. All I need to do is wait a few seconds for the next good scan. I do not leave the RADAR on continuously while cruising, it draws too much power. Most of the time you will use RADAR in poor visibility conditions or to track a vessel to see if you are on a collision course, not rough sea state conditions.

The CRT is the principal power draw on a CRT RADAR. The power pulse is so short that 2KW or 4KW will make little difference in power draw. My 4KW uses 4 amps in standby and 4.5 amps in operation. LCD RADARs use much less power but have poorer resolution than CRTs.

About Furuno 1621, from Al Hatch on Cruising World message board:
Low power drain, picks up an amazing amount of what's on the water, including large power boat waves (took me a while to figure out what I was seeing on this one), small fishing boats, buoys etc ...

Never had a RADAR before this summer and was pleasantly surprised to find out how helpful it is to a singlehander. Big stress relief knowing what's out there in the fog, or that the slow moving tug I've been looking at is not on a collision course. Very helpful at night and in low vis. Most of the time during clear weather I don't use it to save on battery drain. At night I adjust the guard so it only comes up on transmit every 15-20 min., this also keeps the battery drain down to less than 2 amps an hour. On guard it makes a couple of sweeps, no target it goes back to standby, if it finds a target it sounds a tone and automatically stays on transmit.

About JRC 1000, from SheSails on Cruising World message board:
I have used one for 2 years in Maine and Southern New Brunswick and it is a good unit. The screen is just as "tiny" as the Furuno 1621. It has all the features you need, including watch and guard. Power draw is relatively modest, and the 8# dome is good on small boats. I installed mine myself, using an Edson mast mount and RAM swivel arms to bring it out to the companionway, for $1000. An electronics guy checked the tuning for me, made one minor adjustment, and said everything was fine.

Remember range has to do with height above the water. The JRC has a wider beam so it is not as discriminating as the more expensive units. I don't worry about it too much. Am I looking at one lobster boat or two, who cares? I know something is there. It picks up small aluminum skiffs, RADAR reflectors, buoys, the shoreline, and ledges that are awash. If you are groping your way around in the fog, you can "see" a lot more with RADAR than you can with GPS. CARD doesn't do much good for the many boats that are still out there without RADAR.

About JRC 1000, from Larry on Cruising World message board:
Had one. Pros: Light. Easy to operate. Cons: Unreliable. Never trusted it. Sometimes it was accurate. Other times wouldn't pick up a racon buoy. Conclusion: What is an extra few hundred for a unit you can trust? The installation time and materials associated will likely cost more than the unit itself. I spent a week installing mine and in retrospect I wish I had gotten a better unit.

About JRC 1000, from Todd J on Cruising World message board:
Go with the 1500. Only a bit more money, you get much better performance. Practical Sailor rated the 1500 a best buy, where as the 1000 has been criticized for its problems with target resolution due to its low power.

About JRC 1000, from Anthony Powell on the WorldCruising mailing list:
I have had one for about a year and find the LCD display too hard to see. Despite contrast and brightness adjustment, I have found that it is only good at night and even then the font size requires a keen eye for the information (i.e. longs and lats) to be readable.

About JRC, from George S / WA2VNV on Cruising World message board:
Get the 1500, I tried the 1000. Last Jan [2000] at the Atlantic City Sailboat show, I got a great price on the JRC 1000 - 20% off from West Marine. I got it, set it up temporarily and saw the target resolution problem on close in targets. Returned it and got the newer (then) 1500 for about $150 more. Worth the extra $$$. The 1000 has horizontal resolution of 7° / 1.5 kW, the 1500 has 5.2° / 2 kW specs. The Radome for the 1000 is 12" dia, while the 1500 has a 18" dia. The displays are the same - they improved the antenna/scanner unit.

I permanently installed the 1500 last spring, scanner at the spreaders, display at the helm, and interfaced it with the GPS NMEA output. I had several occasions to depend on it. It performs quite well for a ~$1000 priced radar. It only has a 16 NM range, but most of my use is 3 mile and under range. Guard zone alarm works well; screen very viewable in dark and cloudy-bright sun. When tied into the GPS it displays your current waypoint and sort of functions as a chart plotter.

From Richard Lane on rec.boats.electronics newsgroup:
I have used a JRC 1500 for 2 yrs on my sailboat. The only problem seemed to be water vapor entering the display, "fixed" for free under warranty but this year again showed up. I think that the case distorts between the fastening screws allowing moisture to enter where the gasket is not tightly gripped.

From Colin Foster on Cruising World message board:
... there is a time delay when you turn on your RADAR to allow the magnetron to warm up. Actually this time delay is to allow any molecules that have escaped into the tube vacuum to be absorbed by the "getter", before high voltage is applied.
If your RADAR has been off for more than 1 month, the built-in time delay may not be long enough.
If your RADAR has been off for a year, it is quite probable that the time delay is not long enough as I found out the expen$ive way [blew out magnetron].

Add 5 minutes warm-up time for each month the RADAR has been sitting without power on, before you switch to the operate position the first time.
Turn your RADAR on for a few minutes each month to keep the magnetron in good condition.
If you do not have a manual switch to extend
the warm-up time, make sure you use it at least once per month and turn it off a few times before time-out to re-start the timer and get the extra warm-up time.

From George S / WA2VNV on Cruising World message board:
JRC 1500 vs Raytheon RL72: Before I bought the JRC 1000/1500, I had used/tested an RL72 for a few days on a friend's boat on a cruise in Maine. Its good performance is what made me decide to consider getting a radar for my own boat. The RL72 has (I think) a slightly larger screen and footprint (mounting considerations) than the JRC 1500. The performance is slightly better at target resolution. IMHO, I couldn't justify the additional expense (~$300-400) for my intended use (typically less than 3 mile ranges). The features (guard ring, alarms, range settings, etc) are all about the same - with the JRC maybe a little easier to setup/use. My decision was to use the extra $$$ for other things for the boat.

About Raytheon SL72, from Lee Tapper on Cruising World message board:
I have an SL 72 and just completed a cruise from Portland Oregon to Canada. During the cruise we had lots of fog and the RADAR was used extensively.

I really like it and found that it was able to identify other boats - including sail boats and open fishing skiffs with great reliability. It also showed buoys, but I'm not sure how reliable it was on them.

My only complaint is that the SL 72 uses a proprietary interface to communicate RADAR images to other electronic devices. I understand why, this locks you in to Raytheon for other components. It's frustrating to me because there are some cool things I would like to do that involve interface of the RADAR to the PC. Oh well, it's more important that the RADAR do its job than that it interface well.

On the trip I did try to use the alarm feature of the RADAR. I was never able to get it adjusted to the point where it would indicate a boat but not give off a false alarm every minute or so. I don't know if this is a flaw in the RADAR or a cockpit problem with the operator. I would not place the blame on the RADAR without more experimentation. For the moment let's just note that the alarm feature is hard to adjust.
More on Raytheon SL72, from DougR on Cruising World message board:
Well, Lee, now that you mention the alarm, I got it to adjust OK but I have a moderate high frequency hearing loss and would have liked a volume adjustment and a visual warning but I don't think any unit on the market has those options. I noticed the low volume (for my hearing) when setting an anchor watch at Block Island so I had to go back to my Loran for that ... Just another consideration in both unit placement and the disadvantages/advantages of a combo unit.

RADAR antenna placement:
From Erik Hammarlund on Cruising World message board:
The higher the better, up to a point -- then the weight of the antenna and the reduced ability to see close-in objects like buoys start to take a toll. A frequent "compromise height" is about 15 feet off the water. RADAR energy is NOT good for you, so be sure to mount the antenna well above the deck level. Remember that your RADAR transmits about 10-15 degrees below the horizontal plane, when accounting for crew exposure.

From Voyage of the Sailing Vessel Spellbinder:
Just a note here about radar arches on boats. They are attractive, functional, convenient and absolutely useless. When the wind is ablowin' and the waves are gettin' higher, pretty soon you find yourself in 14 foot seas with a radar dome mounted 10 feet above the water. We couldn't see [the boat we were accompanying] until she was about 100 yards away. Take it from us, mount that radar dome as high up the mast as you can.

From Warren on The Live-Aboard List:
Any radar will have a minimum distance its electronics will allow it to "see" independent of the height of the mount. On my Raytheon 2Kw unit this is about 60 feet. Most small boat radars have a vertical beam width or divergence of 25-30 degrees, ie, they can see 12.5-15 degrees above and below horizontal. For 12.5 degrees, the minimum distance to see a target on the water's surface would be:

height of mount = 40
tangent 12.5 = 0.22
40/0.22 = about 180 feet

  • Higher mounting = greater range.

  • RADAR scanner emits microwaves; for safety, mount high above location of people. Especially hazardous to human eyes; should be at least 2 meters away and not in position to be looked into.

SailNet - Sue and Larry's "Installing RADAR"

Learning to Use RADAR:
RADAR trainer software: Starpath RADAR Trainer
From DougR on Cruising World message board:
... it is a simple computer program with lots and lots of good tips in textual material, as well. The screen comes up as a radar screen with all the radio buttons and information as on a regular radar. Then the operator selects a skill and elapsed time level, as well as a task, such as spotting buoys, collision avoidance, navigation, etc. The beauty of the program is that a simple click takes you to 'real time view' so that you can see what you think you are seeing on the radar screen in real visual time. I played with it and it really helps. You become a fairly competent radar reader in less than 5-6 sessions and it is a fabulous refresher at the beginning of each season. ...

From Todd Dunn on Cruising World message board:
To me the best way to learn about your radar is to go out on a clear day when you can see everything. Turn your radar on and start comparing the display to what's actually out there. It won't take you long to understand the relationship between a radar target and reality. Once you get the various targets sorted out you can start fooling around with scales, EBL, guard zones, etc. In no time you will develop confidence in your ability to interpret your radar. When you have that daylight confidence developed, head out on a clear night with a full moon and use the radar. Once again, compare what you can see with the radar display. Another great confidence builder.

Radar trainer programs are OK, but the screens never look like the actual display on your radar. I think using the radar in unlimited visibility is by far the best way to learn how it works in a low stress situation.

From Lee Licata on The Live-Aboard List:
Re: lifetime of RADAR:

I used up the magnetron on my Ray Marine radar after 4 seasons on Lake Michigan. It had just over 500 hours when it failed. Per Ray Marines' tech support, they normally do not last much longer than that.

RADAR reflectivity:
US Sailing's "2007 Radar Reflector Study"
RADAR reflectors reviewed in 9/1/1995 and 8/15/2001 issues of Practical Sailor
RADAR reflectors tested in 10/2000 issue of Cruising World magazine
Article by Dick Honey in 2/15/2002 issue of Practical Sailor
Sea-me RADAR Target Enhancer (X band; about $700)
"Ocean Sentry Radar Target Enhancer" has been discontinued.
ActivEcho from Serpe-Iesm ???


  • Increase the RADAR reflectivity of your boat by putting aluminum-covered Mylar film on the wind-vane, and on sail headboards.

  • Even with a RADAR reflector on your boat, ships can only see you in a 4 to 6 mile range. Farther away, you are a small target. Closer, you are lost in sea noise or below their sweep angle.

  • Many/most commercial ships don't have their RADAR running routinely.

  • Turning on your own RADAR immediately makes you more visible to commercial ship's RADARs.

  • Mobri reflector doesn't work.

  • If your reflector looks like it is hung upside-down, it is correctly hung.

  • Davis' Emergency RADAR Reflector, $25, disassembles and stows flat for storage.

  • Hoist an anodized silver flag.
    Or RADAR Flag ($70 for 12"x18").

  • Temporary: box covered with aluminum foil; aluminized mylar wine bags.

  • When you see a ship, unpack a Mylar "space blanket" and aim it at the ship ?

RADAR Detector

SailNet - Jim Sexton's "Radar Proximity Warning Systems"

C.A.R.D. is $435, have to turn off your RADAR to use it, not useful in high-traffic areas or near airports.

Also "Lokata Watchman".

Also Kelvin Hughes RAD-Seeker RDS-100 (Handheld device with a uni-directional antenna. A built-in speaker turns the RADAR pulse into sound. $250.)

From Will on Cruising World message board:
The [C.A.R.D.] detector circuit works well, but the directional display is just about useless and a gimmick. These things were never meant to work in crowded areas and are well-suited to offshore use. People who throw these RADAR detectors out in favour of RADAR in heavy weather are deluding themselves. RADAR works very poorly in storm conditions with the boat heaving and pitching. I would never sail without a RADAR detector. Yes we know not all boats run RADAR, but crossing the Pacific you far more likely to encounter container ships that must run RADAR by law. I mostly encounter fishing boats that don't run RADAR. With the cost of RADAR dropping even small pleasure boats are now using RADAR and it is quite good having the RADAR detector detect these small craft before you would ever see them on RADAR. Most small LCD RADARs are useless in this regard since they have very wide beamwidths. So in the end a detector is just another device in your survival armoury. These devices are quite reliable. I have my own homebrew one and have tested all the various detectors from the Tamaya, Lokata Watchman and Card. They all have their pros and cons.

From ras on Cruising World message board:
I have had a C.A.R.D. for a couple of years and it did get my attention once that could have have a bad ending. On the down side a lot of false signals, and I have been close to ships that are running RADAR and nothing. But other times the thing has gone off and a ship will come from the direction it said the RADAR was coming from. One night it was going off very strong I saw NOTHING I got the spotlight out and the coast guard was close enough for the light to reflect the red stripe. When I called them on the radio no answer. ... I don't think I'd buy a new one again but if a deal came along why not it can't hurt anything. I sail alone a lot and it never hurt to get up and take a look around at a false alarm.

From Brian Woloshin on Cruising World message board:
I have called ships at sea and asked how I look on RADAR. Their answer has been wait until I warm up the RADAR and I'll tell you. Nuff said.

From JeanneP on Cruising World message board:
We have had the C.A.R.D. unit for almost 10 years and swear by it. Of course, the one we have now is the most recent, after the old one (which was an upgrade of an even older one) got fried by lightning. Not only is it great (picking up radar signals while the ship is still over the horizon and thus out of eyesight), but we have had excellent service and support from the manufacturer. ...

SONAR (fish finder, depth sounder, scanning SONAR)

West Marine's "Depth Transducer Pros and Cons"
West Marine's "How to Select a Fishfinder"
West Marine's "Fishfinder/Sonar Comparison Chart"
Burnet Landreth's "Transducer Maintenance"

From Charles Cohen on the Morgan mailing list:
> What is the difference between a "Depth Sounder", a "Fish Finder",
> and a "Forward Looking Sonar" ?

Depthsounder gives you a number -- depth, right now. Usually includes "depth alarm" feature.

Fishfinder gives you a line -- depth now, depth 5 seconds ago, depth 10 seconds ago, ... you can see the bottom coming up on the display. Also, you get to see echoes from the fish that you pass over. Also, you can sort-of judge how hard the bottom is by how sharp the bottom echo is. I think that a fishfinder (sold to poor fishermen in large numbers) is now cheaper than a depthsounder (sold to rich yachties in small numbers). Includes "depth alarm".

Forward-looking sonar gives a pseudo-3D display of the bottom in front of (and to the side of) the boat. Not cheap ($750 and up from West Marine). I have been told that they're not much good in shallow water -- e.g., the channels of the ICW -- but have no experience.

I've used Humminbird Wide 100 and 100SX fishfinders on two boats; for $100, you can't beat it.
From Gary Elder on the Morgan mailing list:
I pretty much agree with what Charles said. I have talked to manufacturers of the so-called 'forward looking' sounders, and after much cajoling, they all agreed that it is mostly marketing hype. They do look a little bit forward, but still mostly down. They get the "forward 1500 feet" BS by calculating the area 'seen' on the bottom in very deep water. It's mostly a function of cone angle and water depth. Not useful in preventing a grounding.

Even if you rotated a transducer such that it 'looked' forward, you would have a difficult time getting the ducers signal to bounce back to you ... Kind of like throwing a tennis ball away from you. Unless it bounces off a vertical wall, it will tend to keep going away from you.

Forward-looking SONAR:
From Chris Waln on Cruising World message board:
Your eyes are better off up in the rigging looking for water color changes than trying to get useful information from the Interphase or any of the forward looking SONAR that is available for pleasure boats ... if spotting coral is the issue. If you are looking for fish or a contour line before you actually cross it on a steep to shore maybe they are useful.

They do not have the power or sensitivity to give you a reliable picture of high scatter bottom features such as coral and the false alarm rate is so high you'll turn it off for peace of mind rather than turn it on. ...

From Lector on Cruising World message board:
Way oversold ...

We took ours out and sent it to consignment.

To be truly useful, they have to be mounted at the bow. Since they look forward at about a 45 degree angle, they can't see much farther ahead than the water is deep. If you are in deep water looking for fish, fine.

If you are in shallow water looking for trouble (before it finds you) consider the following.

In twenty feet of water, ... at 6 kts you are moving about 9 feet a second ... so even if in the bow it's only going to give you about 2 seconds warning. If it's amidships and you are on a 40 footer it's going to see the bottom under the bow.


[Display tends to distract helmsman from heads-up sailing.]
[Transducer is bulky, and expensive to replace.]
[Pitching and heeling affects them.]
[Lots of false alarms.]

From Todd J on Cruising World message board:
I used one for two years.

If you are going to use them for fishing, great, but if you want to navigate shallows, forget it. They are completely inneffective in shallow water, which is where you need them. The shallower the water, the shorter the distance you can see forward.

Big, obtrusive transducer that will slow you down.

From Rick on Cruising World message board:
More hype and advertising than substance.

Especially if it is interphase technologies ... the things work fine in deep water and will tell you when it is coming up, but in 8-15 foot of water they are basically worthless ... and interphase technologies are a bunch of jerks ...

From Logan S/V Scotty Ann on Cruising World message board:
Used one in Indonesia last April and I was very impressed. The damn thing really does sort out the reefs and bumps ahead of you quite well. I was pretty impressed by the cost too. In our experience, with reasonable light, you can see what you need to see before you hit it almost always. The charts are pretty good at keeping you off things too if you pay attention and don't put too much reliance on the GPS. In some parts of the world things are out of the charted position by GPS but right on by bearings. Still, if I had that kind of money I would consider one. They are cool.

From B King on Cruising World message board:
Interphase: I have one, you have to pull the boat to put it in. It works well, there is a learning curve to using it. It will not tell you much if you are in very shallow water (i.e. ICW). It told me I was in 7ft ... 6ft ... 5ft, too late on bottom. It works great finding fish in front of you and will tell you if you are coming up on a shallow area from deep water.

From Paul Martin on rec.boats.cruising newsgroup:
A friend of mine installed a forward looking sonar in his Freja 39 in 1980. He took it out a year later. His opinion was that it was useless as a safety device. It couldn't pick out an opening in a reef without being so close that the boat was practically in the surf line before he could discern anything. He said he could tell more from on deck (which is where anyone belongs) then down below with his head stuck in a sonar hood.

From Susan Meckley on the IRBS live-aboard mailing list:
Take a serious look at the Raytheon Model L365 fish finder ... depth, speed, knot log, and temp ... plus you can see the bottom before you anchor ... all for $230 (West Marine) ... for thru-hull $400.

Certainly a lot cheaper than todays 'separate' instruments. Plus only one thru hull. This model provides a complete kit of everything needed to do the job.

I recently installed one on my boat...And yes, I am the electronics mgr at West Marine/Oakland, however, this is one option I always mention to boaters who are looking for such parameters.

AND unlike other fish finders, it has a screen that gives '3-D' info on the fish...if you're so inclined to fish.

From Norm on the IRBS live-aboard mailing list:
Do not let the extras such as speed and distance readouts influence your choice. These bits of info are available elsewhere, your GPS or Loran, and with MUCH more accuracy. As the speed transducer fouls, and it always does, the speed (and distance calculated from this speed) becomes more and more unreliable.

Temperature is almost useless unless you are looking for the Gulf Stream or are an expert fisherman.

I also suggest, unless the unit is a "sealed in dry nitrogen" type, open it up when you install it and insert a dry packet of silica gel or one cold or wet day you will find a fogged-over screen as has happened to me (in fact the fogged-over area on the instrument was right over the depth number!).

But I heartily second Sue's recommendation of a fish finder rather than a simple number readout because it will vividly show bottom contours and trends as well as (with a white line unit) show the softness or hardness of the bottom.

From Bob Clark on IRBS live-aboard mailing list:
... I'm not entirely happy with my Apelco 265. Occasionally it will suddenly lose contact with the bottom, sometimes at a time when we're entering a cove or something. I have a friend with the same unit and the same problem. He says he called Apelco, and was told... too bad, it's a fishfinder, not a depth sounder. ...

From Larry / CT on Cruising World message board:
[Re: Depth sounder accuracy; intermittent bad readings and false alarms:]

Water turbulence at speed, bubbles, reflections from the keel (if transponder mounted too close to keel) and soft bottoms all can cause momentary erroneous readings. I think all brands have this issue.

Stereo, TV

"Television? The word is half Greek and half Latin.
No good will come of it."
- C. P. Scott

From Tim C, SG, Geres and others on Cruising World message board:
  • Don't get "marine" equipment; get automobile equipment.
    [Unless the equipment will be exposed to spray.]

  • Proper marine speakers are the way to go for the sound (in the cockpit ?). I tried great sounding patio speakers but the magnetic interference was terrible and would throw the compass off 10 degrees. So spend the bucks on poly planar or some such speakers that are shielded.

  • When replacing the (dead) auto radio in our boat we considered another car stereo, but instead spent about $75 for a smaller "boom box" from WalMart and powered it on DC using a Radio Shack adapter on a cigarette plug cable. It lashes down below with a simple bungee cord but (this is the nice part) can be easily taken on deck in nice weather while sailing or for dinner music at anchor. Also, no holes to cut in cabinetry , etc.

  • I got a 9" TV/VCR at Costco for around $200. It runs on any voltage from 12-250 v. It shuts itself off at 11 v so it won't drain your battery completely. It burns 35 watts.

  • The Bose 151 marine speakers are great. Another (not so great -- but very good) option are the Polyplanars. They have shielded models which you might consider in the cockpit, plus they have a very durable weather reputation. I thought the sound wasn't as nice, so I'd use the Bose below.

From a couple of people on BoaterEd forum:
"A regular 120 VAC TV/VCR combo with a 300W Portawattz will be cheaper than a 12 VDC TV. I bought a 13" Sanyo TV/VCR on sale in July [2000] and paid $140 and the inverter is only about $30."

From RobH on BoaterEd forum:
In most major truckstops (Pilot, Petro, T/A) you can find a brand of TV that is called "KEC". They make a 13" TV that is both 120VAC and 12VDC. You get two different power cords with it. I can vouch for the absolute "toughness". I had one of those TV's drop 5 feet to the deck ... and just like the proverbial "Timex" it kept on ticking. These TV's are antenna and cable ready. The only downside is that if you want to watch a movie you have to have a separate VCR. Price on TV is around $139 or so. If it ever has to be repaired, they pretty much do it at "flat rate", which is actually pretty cheap. I have two of these TV's. Oh, they come with remote too. So you can avoid that "long walk to the TV inside a semi-tractor".

From Rick Anderson on the WorldCruising mailing list 12/2000:

Here in Oz there is a variety of new 12 volt equipment on market, including "marinised" versions, with TV and VCR integrated into one case. Increasingly, VCRs and TVs here support both PAL and NTSC.

But as a low-cost option (and I assume this is what you seek instead of using an inverter), check with the workshops for a long range coach company. I had a 12 volt VCR Player only, that came from a coach company, where their policy was to replace faulty units from buses, then have the discards repaired and sold. ...

From Doug Barnard on the SailNet liveaboard-list:
For me, the USB TV adapters aren't worth it. I guess if you want to put up a 320 X 240 window to be able to check the weather reports, fine. I couldn't really watch full-screen, and that was with a satellite feed. USB doesn't have the bandwidth to do it properly. There are some Firewire adapters, but in the $200+ range.

Long story short, I bought a flat screen TV from Best Buy.

12V DC TV's with CRT's take a fair amount of power to run. Pay attention to the amps/watts rating when buying.

TV Antenna:
From Bob Young on the IRBS live-aboard mailing list, about making your own portable TV antenna:
Get a 6 ft length of aluminum strip, and a 2 ft piece of 1" x 2" lumber. Cut the aluminum strip into 2 equal 3-ft lengths, drill a small hole near each end, bend each strip to a semi-circle, and attach to the ends of the piece of wood with a single screw at each end. Leave a gap between the ends of the aluminum strips where they are attached to the wood - - the 2 halves must be electrically insulaated from each other. Buy a 300 ohm to 75 ohm matching transformer from Radio Shack, and enough 75 ohm coaxial cable to reach your TV from the hoisted position. Attach the 2 spade terminals of the transformer to the 2 screws at one end of the wood, and the coaxial cable to the other end of the transformer with a screw-on plug. Make a simple bridle from light line to attach the whole rig to a halyard, hoist it up, and use a downhaul line to stabilize it.

I made one as above for a cost of about $10, and it worked extremely well, pulling in stations from over 100 miles away. It is omni-directional, but some adjustment to the hoisted position may be needed to minimize ghosting. If even more gain is needed, Radio Shack sells a cheap signal amplifier (about $15), The amplifier should be attached at the antenna, and the power injector at the TV. Only drawback to this is that you need 110 vac supply.

From fmstone on the IRBS live-aboard mailing list, about TV antenna:
BoatU.S. sells a TV antenna made to hoist in the rigging ["Boatenna" ?]. It is made for 300 Ohm twin lead wire but Radio Shack carries an exterior 300 Ohm balanced to 75 Ohm coax transformer for about $2. We mounted ours on the mizzen top and it is great. No electronics and no power required. It works as well as the fancy electronic ones it replaced after two failed.

From Fred on "Legacy":
Met a trawler on the ICW that had gone through 3 or 4 of the fancy electronic antennae, and none of them worked well.

Make a circular dipole antenna: bend two strips of aluminum into half-circles, attach an antenna lead to one end of each, mount them in a circle, hoist into rigging so circle is parallel to the water.

Maybe add an amplifier unit from Radio Shack.

A dipole for TV frequencies:
Dipole overall length in meters = 142.7 / frequency in MHz.
TV frequencies are about 54 MHz (ch 2) to 214 MHz (ch 13).
So dipole overall length = about 2.6 meters to 0.7 meter.
Circular dipole diameter = about .8 meter to 0.2 meter.

From Kevin Haddock on Low-Cost Voyaging mailing list:
Try using the VHF radio antenna mounted at the top of your mast.

From "Alyra" (I'm sure I've spelled it wrong):
At an RV store, you can buy a unit which is about 4" x 10", acts as antenna and amplifier, comes with wire, runs on AC or DC, costs about $75. Works well.

From Keith on The Live-Aboard List:
Re: Omni-directional TV Antenna

The last time Powerboat Reports tested, here is what they came up with: They liked the Shakespeare 2030 and Naval PR-411 the best. They also liked the Dantronics Status with an adjustable gain control. The Naval and Dantronics lines are used a lot on commercial vessels. ...

[later ...]

I bought a Shakespeare 2050 TV antenna last year. This was tested by Powerboat Reports and said to be one of the best for marinas, etc. because it was "aimable" and amplified. It is a round antenna and the array inside rotates 360 degrees to aim at the transmitting station. It has a little remote box on the TV and a wireless remote to control it.

Basically, this thing is worthless because it is unreliable.

The first unit I purchased just wouldn't work at all. The remote would indicate that the antenna was turning, but it wasn't. I contacted Shakespeare, who put me in touch with the company who actually built it. They sent me another wireless remote setup. Didn't help. Sent me a wired remote unit, didn't help. I finally got disgusted and took the whole thing back to West Marine for a warranty replacement. It worked for a while. Many times, I would come into the cabin and the remote box on the TV would indicate that the antenna was turning, with no request from me to do so, and was against the stop on one side or another. The motor started grinding whenever the array was rotating. Finally, yesterday I turned the A/C power off, then back on, and the remote box on the TV lit up all 4 LEDs, indicating that the unit was rotating both clockwise and counterclockwise at the same time, and was against the stops on both ends. Of course, it died after that.

On top of all that, this is one of the units that the USCG warned that defective transistors in a few units would mess up your GPS. Mine didn't have this problem, but this entire unit is a POS. Fair warning. I'm going to try to take it back and get my money back at West if it's still under warranty. If they won't take it, I'm going to raise heck with Shakespeare. Wish me luck.

From Captain Ric on The Live-Aboard List:
On my old boat I had the round fiberglass-covered 21" diameter non-rotating amplified TV antenna from Shakespeare. It, like the 2050, I'm afraid, is also worthless. On my new boat I have a Hinkley TV antenna installed. It looks like just a metal loop to me but it works much better than the Shakespeare ever did. I also have a KVH-4 satellite antenna for DirecTv. That really works great but doesn't get local channels.

From Ed Kelly on The Live-Aboard List, 4/2003:
Warning on TV Antennas Causing GPS Jamming Danger

Early this year there were horrible problems tracking down RF energy that was being broadcast from TV antennas that had gone bad without knowledge of the owners. It had the effect of a GPS Jamming device. They were dangerous as they knocked out GPS usability, not just on the subject boat, but on other boats as well. Be forewarned. If your TV antenna has a preamp in it, its malfunction may destroy GPS functionality for you and neighbors even without your knowledge.

The TV and antenna did not even have to appear to be on. It was quite a nightmare tracking down the source when it happened in California. It was quite easy to knock out the GPS.

Released 01 January 2003:

The U.S. Coast Guard warns mariners that some marine television antennas may result in inaccurate position information or loss of GPS signals. Interference is not necessarily limited to GPS equipment on board the vessel with the antenna, but could affect craft some distance away.

The Federal Communications Commission has identified the following models of antennas as having potential problems affecting GPS: Tandy Distribution Products Electronics, MINI STATE Electronic Amplified UHF/VHF TV Antenna - Models 5MS740, 5MS750, 5MS921; Radio Shack Corporation, Long Range Amplified Omni Directional TV Antenna - Model 15-1624; Shakespeare Corporation SeaWatch - Models 2040. The Coastguard is, however, stressing that the problem may occur with other antennae.

Any mariner, with a marine TV antenna, experiencing a lack of signal or degradation of GPS operation, should perform a test. If turning off power to the TV antenna results in improvement in GPS performance, the mariner should contact the manufacturer of the antenna and identify the symptoms. If the antenna is not listed above, or if switching off a TV antenna does not improve performance, the Coast Guard requests that mariners contact the Navigation Information Service.

From Lee Haefele on World-Cruising mailing list 7/2005:
Re: Bicycle wheel TV antenna:

You would need to cut a notch out of the wheel and connect a wire to each side. It would be best to then use a 300 ohm to 75 ohm coax matching transformer; I think Radio Shack still sells these in an outdoor weatherproof model. If on a budget, just connect the coax shield to one side, the center conductor to the other, then seal the cable with lots of silicone caulk.

The best TV for a boat in US coastal waters would be a new digital model, these would fix all the harbor reception problems. The stations are mostly up and running now, and usually have 2 stations on each, so there is more programming. Problem at the moment is that smaller size sets do not include a digital tuner yet, so you would need a second, $250 box the size of a cable box or DVD. The sets should be available with integrated tuners in a year or so.

From Denece Vincent on the IRBS live-aboard mailing list, about a car stereo on a boat:
One caveat to the car CD changer with remote: the remote requires the system to be in a 'sleep' but not 'off' state, so it does cause the radio to use quite a bit of juice even when off, unless you turn it off at the breaker (which loses our presets); apparently there is some feature in car wiring that works differently (or it could be my wiring job).

Marine stereo test article in 4/1/2001 issue of Practical Sailor.

From "Get Smart":
TV repairman: "Okay, all done, here's the bill."
Max: "Is that your phone number there at the bottom ?"
TV repairman: "No, that's the total. A phone number only has seven digits."