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January 2012

Outboard Motor

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"A knot is pretty much like a mile per hour, but more expensive."
-- P. J. O'Rourke

Engine    Pistons on crankshaft

Diesel versus gasoline:
Diesel better:
  • More MPG.
  • Fuel safer (less volatile; higher ignition temperature).
    But you'll still carry gasoline for dinghy, and probably propane for cooking.
  • More reliable (because less electrical) ?
  • Fuel easier to get at marinas.
  • Fuel cheaper.
  • Less electrical stuff to corrode.
  • Less electrical "noise" because no ignition system.
  • Produces far less carbon monoxide in exhaust.
  • Easier to resell boat, because of perceived safety issue.
  • Cheaper to insure boat, because of perceived safety issue ?
Gasoline better:
  • Much cheaper to repair and replace.
  • Less sensitive to overheating.
  • Less sensitive to dirty fuel.
  • Can change oil less often.
  • Less starting battery power needed.
  • More chance of being able to hand-crank-start it (lower compression).
  • Lighter weight.
  • Smoother and quieter (because usually more cylinders).
  • Runs cooler.

David Pascoe's "Gas -vs- Diesel"

From Jeff H on Cruising World message board:
I personally think gas inboard engines have gotten a bad rap. I have had nothing but good luck with them. Here is how I see the two.

Gas engines produce more horsepower and about equal torque for the pound of engine weight but gas engines turn at faster speeds to do so. Gas engines start easier in cold weather than a diesel.

Gas engines depend on electrical components more than diesels and in a marine environment electrical components require more attention and all electrical elements are sealed or spark free in design. So with a gas engine you do more short term maintenance. With a diesel you tend to go for years merely changing lube oil and fuel filters and then you get hit with the really big bill as a injector pump needs work

Diesels are noisier and vibrate more. The parts are more robust but the loads are greater requiring more expensive parts which only last a little longer. Popular gas engines went out of production quite a while back and so gas engines tend to be older and therefore a little less reliable mostly due to age.

Gas is a more explosive fuel so precautions must be taken in handling gasoline and using gas engines. Gas engines need engine room vents and blowers. Fueling requires careful clean-up and power venting of the bilge area. Fuel lines need special care. Diesel is supposed to be safer. On the other hand almost every sailboat I have ever known about that burned or blew up had a diesel. There is nothing more dangerous than a diesel boat with a propane system since they should have a bilge blower and follow the same procedures as a gas boat but never do.

The shame is that no one really makes gas auxiliaries anymore. That's my opinion!

Newest diesels: horsepower/weight ratio is almost as good as that of gasoline engines.

From Bob Kunath on Great-loop mailing list:
In general, diesels use about 1/3 less fuel, boats otherwise equal. That's because diesel weighs more than gasoline, and is more efficient. In addition, I understand the average cost per gallon is about $.50 less per gallon.

Far more important than the fuel type is speed. If you buy a displacement hull, such as most trawlers, and stay at hull speed (a displacement 40' hull will get about 8 knots) you will get about 3-4 miles per gallon diesel. There are very few displacement hulls with gas engines. Planing hulls, typically with gas engines, must get on plane to be efficient, typically at about 12-15 knots. One mile per gallon is typical for smaller boats, say about 25-30 feet. Larger boats use much more gasoline.

From Robert Reib on Great-loop mailing list:
When I compare diesel and gas vessels by Horsepower I discover one basic truth. The larger the engines in vessels of the same length, the higher the fuel consumption to go the same distance (whether gas or diesel). More horsepower equals more fuel consumed, even if you go faster.

Two more points. Maintenance on gas engines is usually more critical than on diesel engines, particularly in salt water. Electrical ignition systems are particularly susceptible to problems in a high moisture environment found in most boats. Diesels don't have this problem.

Finally, fuel costs. The average cost of diesel fuel on the East Coast in June 2002 was $1.27/gallon. Gasoline averaged $1.74/gallon. So a gasoline boat using the same amount of fuel as a diesel boat will pay an average 37% more for fuel, based just on fuel costs. To make matters worse, most long-distance diesel boats can pick and choose where to fuel up. Thus you can travel the entire East Coast paying less than $1.00/gallon for diesel fuel, and save even more over the $1.27 average I just quoted. Most gasoline boats have to fuel up far more often and end up paying much nearer the average of $1.74. There are many marinas on the East Coast that routinely charge $2.00 or more per gallon for gasoline, while I did not find any that charged that much for diesel. In the opposite vein, I found dozens of marinas that charge $1.00/gallon or less for diesel, but did not find any marinas that charge less than $1.65/gallon for gas. Bottom line, gas will cost you more to buy than diesel.

What type of boat to buy is a complicated question. You can't decide based on gas vs. diesel. You must look at what you plan to do with the boat and how you will use it. That said, I will generalize. If you are concerned about costs but have time on your side, buy a vessel with a small single diesel engine. If you are concerned about time and not on a tight budget get a fast gasoline boat with twin engines. On the two extremes I will compare fuel costs for doing the Great Circle Route. A 36' Krogen Manatee with a 50 HP single diesel engine can complete the Great Circle Route for about $600 in fuel costs. A 36' Bayliner with twin 310 HP gas engines can complete the Great Circle Route for about $13,000 in fuel costs. When you finish with the boat you can usually get back as much or more as you paid for a Krogen Manatee. With a gasoline boat you will have much the same depreciation as on a car.

From Larry Zeitlin on Great-loop mailing list:
1. Diesels DO use less fuel than gasoline engines. Part of this is due to higher efficiency of the diesel engine because of much higher compression ratios. Part due to the diesel's ability to burn extremely lean mixtures at part throttle. Part is due to the fact that diesel fuel weighs more than gasoline and has about 20% higher energy content. Since we buy fuel by the gallon, rather than by the pound or by its BTU content, a diesel gets more power out of a given volume of fuel. The usually accepted figures are that a diesel gets 20 hp for an hour out of a gallon of diesel fuel while a gasoline engine gets 13 hp for an hour out of a gallon of gasoline. And, as pointed out, diesel fuel tends to sell for less at most locations.

2. Diesel engines DO last longer than gasoline engines. A diesel engine must be more strongly constructed than a gasoline engine to withstand the higher compression ratios and peak cylinder pressures. Long life is a payoff for this ruggedness. On the other hand, diesel engines are much heavier than the equivalent gas engine, cost twice as much to begin with, and are far more expensive to repair. If you have priced an injection pump recently, you know what I mean. Additionally, diesel mechanics are rarer and charge more than gasoline engine mechanics. Modern diesels are almost as electrically dependent as are gasoline engines so the issue of environmentally degraded electronics is the same for both types.

3. Although diesel engines last longer, their higher initial cost makes the total life cycle cost for both types of engine comparable. Diesel fuel is inherently less dangerous than gasoline ...

4. SPEED is by far the most important determinant of fuel consumption. The power required to propel a boat tends to rise as the CUBE of the speed. It doesn't matter if the power plant is gasoline or diesel. As an example, a 40' long, 20,000 lb trawler will take about 29 hp to travel at its hull speed of 8.5 kts. If we drop the speed to 6 kts, it only takes 10 hp to propel the boat. This is a 66% fuel saving at the cost of a 30% speed drop. Admittedly, on a 50 mile trip leg the faster boat will arrive in slightly under 6 hours while the slower boat will take about 8 hours, a difference of a bit more than 2 hours. However the sailors on the slower boat will save enough on fuel to blow themselves to a gourmet meal while those on the faster boat will eat hot dogs. At velocities higher than hull speed the fuel cost rises to absurd levels. If you want to go fast, travel by plane.

Gasoline outboard motor as main engine:
  • Smaller and lighter.
  • Easy to remove and take to service shop.
  • Could carry a complete spare motor if desired.
  • Keeps gasoline outside the boat.
  • Doesn't take up space inside the boat.
  • Can pivot to provide thrust in many directions; more maneuverable.
  • Outboards designed to run small props at high RPM for relatively short time; sailboats want big prop at low RPM for long time.
  • Vulnerable to theft or loss.
  • If boat is pitching heavily, prop can ventilate or motor can get submerged.
  • Higher fuel costs (gas versus diesel) and higher fuel consumption (2-stroke versus 4-stroke).
  • Appropriate / economical only for smaller boats ? Large outboards are expensive and heavy.
  • More of a one-piece / throw-away-if-it-breaks item, rather than a set of discrete units like engine / transmission / shaft / prop of an inboard.
  • Probably has a shorter lifetime than an inboard engine. Especially 2-stroke outboard, because of lubrication system.
  • Steering/throttle control can be inconvenient.
  • Boat transom may not be reinforced enough to handle the stress.
  • Boat turning radius may be very large.
  • Reverse may be very bad.

Diesel overview article by Quentin Warren in 6/2000 issue of Blue Water Sailing magazine
Diesel engines database
David Pascoe's "Diesel Maintenance Or Lack Thereof"
BoatSafe's "The Life Expectancy of the Marine Engine"
SailNet - Sue and Larry's "Replacing the Diesel Engine"
"To Repower or Not to Repower ..." article by Jim Wolstenholme in Feb 2002 issue of Blue Water Sailing magazine (flowcharts to aid decision-making)
Repowering article by Darrell Nicholson in 2/2003 issue of Cruising World magazine
SailNet - Tom Wood's "Surveying a Diesel Engine"
BoatU.S.'s "Exhaust and Fuel Hoses"
"Secondary Engine Loads" article by Don Casey in Nov/Dec 2001 issue of Blue Water Sailing magazine
SailNet - Ben Hilke's "Runaway Diesel Engine"

Nice book: "Keep Your Marine Diesel Running" by Richard Thiel.
Covers theory, operation, some maintenance in very clear way.

Some diesels have a "pre-combustion" chamber on each cylinder, with injector and a glow-plug in it. Others just inject straight into the chamber on top of the piston, with no glow-plug. The "pre-combustion" chamber keeps any "detonation shock wave" away from the piston and valves, and allows lighter pistons, but makes starting harder.

Diesel engine prices:
From TimS on Cruising World message board:
My 2 cyl. Pisces 27 (marinized Isuzu) needs a rebuild on account of water leaking back into the cylinders from a corroded water lift muffler. I have three options:
1. Rebuild the Pisces for ~ $2800.
2. Replace with a rebuilt early 90s Yanmar 3GM30F ~$5000
3. New Yanmar ~$8000 installed
More from TimS, 6-12 months later on Cruising World message board:
I had to have my 27 HP diesel rebuilt last year due to a corroded waterlift muffler. Water back filled into the combustion chamber. When water gets into the cylinders it becomes superheated during the combustion cycle and essentially steam-cleans the piston walls, removing all the lubricating effect and resulting in scoring of the walls by the rings as well as corrosion on the cylinder heads. The rebuild set me back $4K.

And: remove/rebuild/reinstall injector pump for Westerbeke 4 cyl diesel == $1000 - $1400.

From SailNet - Sue and Larry's "Replacing the Diesel Engine":
Repowering with a new 100 HP Yanmar, transmission and shaft: about $20k; can save $4k by doing some of the work yourself.

From Jeff Twiss on Cruising World message board, 8/2000:
Re: how much does a new 3 cyl Yanmar cost ?

Quick estimate from my mechanic: $8500 for a Yanmar [40 hp 3JH2] to replace our 40 hp diesel. That is just the engine - count on another $1500 to install it by LA prices (assuming no difficulties).
More from Jeff Twiss on Cruising World message board, 10/2000:
We replaced a 20 yr old 40 hp Thornycroft with 40 hp Yanmar 3JHE. The cost were as follows:

Engine $8100 (list is about $10,500) Labor (40hrs) 2400 (LA rates) Towing/lifts 282 Misc parts 627 Total (less tax on engine and parts) $11409.

OUCH ... I had not added up the bottom line until just now -- but, it was almost a turnkey job. I did much of disconnecting the old engine myself but left the remainder up to the pros. New engine came with transmission, mounts, 80 amp alt, and instrument panel. Extra parts above included new stringers, shaft flange, fuel and water hose, exhaust riser and hose, wood for stringers, mount and crankshaft pulley for 2nd alternator. Additionally, I spent about $250 on a new raw water strainer, bilgekote paint and supplies, insulation, some fasteners and marine plywood to reconstruct cover for engine compartment.

Thanks again for all the input/opinions on whether to repower. I took an inaugural run last pm and I'm quite pleased with how it turned out. That new engine purrs. Plus I now have one tidy engine room.

From Bill Ferguson on Cruising World message board:
New Engine costs: Varies a lot depending on condition of engine bed and exhaust system etc. We paid about $11,000 for a 27 hp Yanmar. Engine alone cost about $7,400. We needed a new drive shaft (longer) and cutless bearing so the price really includes lots of surrounding items. ...

From Dave C. on Cruising World message board 12/2000:
I repowered a Cal 34 (displ 9500 lbs) with a westerbeke 30-B3. The engine was about $6K. The installation which included new beds, but NOT removal of the old engine (another Westerbeke), was about $9K.

From Al Herrle on SailNet's Gulfstar mailing list 8/2003:
From Trans Atlantic Diesels, for the 6-354.4 engine. (This is a non turbo engine, turbo prices are different.)

1. Rebuilt Long block $4550 exchange.
2. Rebuilt Long Block with remanufactured fuel injector pump and injectors is $5250 exchange.
3. Rebuilt with all new marine accessories for $6750 exchange.

From Howell Cooper on SailNet's Gulfstar mailing list:
We repowered [in 2002] and found that engines are available that fit close to the footprint and yet have more HP at lower RPM. We replaced a Perkins 4-108 with a Westerbeke 55 A Four which developed 55 hp at 3600 RPM. It came with a transmission and new alternator. In fact, it actually fit the engine ways width-wise and was actually shorter. The advantage to ordering the engine with transmission is that it is matched to the HP and you can select the right ratio to match your propeller. ... there are show discounts which are applied to even factory orders ...

The Westerbeke 55A Four is now a 55B Four due to some changes required to meet new environmental standards. It actually develops 55 hp at 3000 RPM. I understand that most of the new engines above about 60 hp are turbocharged to meet the new standards. ... Our bottom line on the repower with new everything including new control panel was just under $13K. I did do much of the preparation for the extraction myself. I think that this number is greatly dependent on the area in which you have it done. I actually sold the old Perk (with unknown number of hours) for $1500. That made our net net $11.5K.

One really great thing about ripping the old Perk out was that I could get to the bilge. I did a number on that area and actually used white paint to redo the bilge and the engine room. I actually found 20 years worth of screws, seals, engine parts and a burnt screw driver in there. When we fired up the new engine, it did cover that space with tiny red paint specs from the fan belt and other stuff that quickly shed the paint.

From Brett Hoopes on SailNet's Gulfstar mailing list:
My wife and I have a Gulfstar 44 and [2002/2003] did a repower. ...

The long and short here is that I went with the Perkins M54, reason was that the M54 happens to also be the Caterpillar motor, Volvo motor, and a couple others that I can not remember. Each company painted them different colors and did some modifications but the bottom line is it is the same motor. Next thing is it is not turbo ...

During this change we cleaned and put new insulation in the room to make it even more quiet than this motor already was. (side bar, a lot of charter companies are starting to install these motors.) After all was said and done, you can hardly hear the motor run when she is at max RPM which is at 2200, oh ya, I only burn .6 gallons an hour doing 7.3 knots. (sorry guys, I am one of those with a max prop, but I can reverse so easy.)

Total price: motor was $9,000, install was $5,000 including the removal of the old motor. ...

From Jeffrey Kay on SailNet's Gulfstar mailing list:
I repowered my Gulfstar 44 [in 1999/2000]. I went with the Yanmar 66 HP turbo. It's now got about 600 hours on it, and no problems. We average close to 8 kts over water at 3000 RPM. Very smooth, no smoke. I rebuilt and kept the old tranny. Although the footprint was smaller than the Perk, the existing rails work ... although we had new mounts custom made. Total job was $14k start to finish including a new exhaust system.

There is nothing like new!


[Late 2004:] I paid $14,500 installed for my new Yanmar 66 HP in 1999. This included custom mounts and a new exhaust. The boat's previous owner had neglected his Perkins. The cylinder head was cracked, all cylinders were scored. I was quoted $9,000 to rebuild the Perkins. I would have been crazy to do it. The Yanmar is quiet, fuel-efficient and RELIABLE!

From article by Steve D'Antonio in 10/2002 issue of Cruising World magazine:
Diesel engines ranging from 47 HP to 67 HP, with transmission, list prices range from $7K to $10K.

From BryanJ on Latitudes and Attitudes Cruisers Forum:
Regarding fuel consumption, diesels burn fuel at X pounds/hour/HP. So if you use, say, 18 HP to cruise, you should not see any difference in fuel consumption regardless of the engine size.

From Bill Adams on Cruising World message board:
Most marine Diesels suffer from two things that diesels hate the most ... disuse and lousy fuel. With that in mind, there aren't too many actually bad choices in diesels. Volvo, Yanmar, Perkins, etc. all make fine products that should last for a lifetime. The difficulties arise when the engines sit in a cold, damp bilge for months on end with only an occasional startup and a short run time. Old fuel in the tank cycles through heat and cold, condensation and bacteria build up and gunk up the works. Diligent preventive maintenance and clean fuel is the secret to long life.

In terms of reliability, efficiency, noise there isn't one brand better than the other. ...

From Billy on Cruising World message board:
Moisture is the killer of diesel engines. Not being run enough or more importantly hard enough when they are used is the problem. Diesel engines burn colder than gasoline engines thus need longer to warm up properly. They also generally need to be run harder than gas engines to heat up enough to drive the moisture out of the castings. ...

From's "Cruising Tips":
Run your diesel engine hard every so often. This seems contrary to common sense but it is good for the engine to run it really hard every 10 hours or so. Most cruisers normally run their engines at much slower speeds than is optimum for the engine design because the fuel consumption is less and the range is greater. However, by running the engine for 5 or 10 minutes - or more - hard every ten hours, you can blow out a lot of the carbon that builds up on the valves. When we run ours hard, small chunks of black carbon and black water spew out for 3-4 minutes and then the exhaust and water clears up.

From Patrick Gerety / Willard Marine on the WorldCruising mailing list 12/2000:

Every engine builder that I am aware of specifies that a marine diesel engine should be run at 60% to 80% of maximum rated RPM about 80% of the time (in other words cruising speed).

Modern marine diesel engines do not like to run at less than 60% of their maximum rated RPM's for long periods of time. You are not saving your engine by throttling back. You are actually causing damage to its longevity. Marine diesel engines like to be run hard and run often. Anything else can have disastrous effects. If you run the engine according to the manufacturers specifications you should expect to get 10,000 plus hours from a properly maintained engine. Anything less and you take your chances. I have heard of some engines failing after only 300 hours.


From Karl Denninger on The Live-Aboard List:
Light load is not the issue with diesels.

Being unable to maintain operating temperature and low linear piston speed IS.

If your diesel is running cold - certainly under 150 degrees - you're asking for trouble. Ditto if you're leaving it at its "regular" idle regardless of load.

This, by the way, is why truckers and others with big diesels (including engines such as diesel locomotives!) "idle them up" and never let them sit at low idle for very long.

Engines have their clearances and mechanical parts sized and designed to run at a certain temperature. For fresh-water-cooled marine engines this is typically in the 175-185 range, with newer engines sometimes being designed to run as high as 190-195.

For diesels there is a second problem - low cylinder temperature and low piston velocity together permit small amounts of fuel to remain in the cylinder in liquid form. This then washes down the cylinder walls and into the oil. The result is severe dilution of the lubricating properties of the oil and consequential bearing damage.

This doesn't happen with gas engines due to the higher volatility of gasoline vs. diesel fuel, but gas engines are subject to the temperature-related issues.

Finally, there is another consideration - maintenance schedules are typically set based on engine hours. This means that the practice of running engines in this fashion leads directly to more maintenance.

If you're running your diesel at 1500 RPM to charge, and it maintains a reasonable operating temperature, even out of gear, you're unlikely to damage it.

But if you're letting it idle at 500 RPM you probably will, EVEN IF YOU ARE IN GEAR. Better to take the engine OUT of gear and bump the idle up to 1000-1500 RPM.

(This is, by the way, why diesel manufacturers strongly recommend AGAINST trolling at idle for extended periods of time without intervening operation for 10-15 minutes every hour or so a high enough output level to burn off any accumulated fuel and deposits. The engines wet stack and damage results.)

From Sea magazine:
10 Tips for Longer Inboard Life
  1. Clean the engine.
  2. Prop it right.
  3. Keep it dry.
  4. Optimize the exhaust.
  5. Lubricate to the max.
  6. Correct any misalignment.
  7. Install more gauges.
  8. Coddle that water pump.
  9. Add freshwater cooling.
  10. Clean up the fuel system.
-- Gordon Groene

Mostly from "How To Buy The Best Sailboat" by Chuck Gustafson:
  • Need 3 HP / ton to move boat at hull speed through flat water.
  • Want fuel cutoffs at the fuel tank and engine.
  • Blower in engine compartment should be mounted high, but have intake as low as possible (must be in lowest 1/3 of compartment).
  • Want drip pan under engine.

From Howell Cooper on SailNet's Gulfstar mailing list:
Oil drip pan:

Although our GS40 came with a fiberglass pan under the old Perk, I started using a throwaway aluminum turkey pan on top of it. You can bend it to get it in place, then bend it to remove it. Inside that, I used Pig Mats. Pig mats are commercial brand oil absorbers much better than the ones sold in the marine stores but cheaper by the box. The company is New Pig and they make all sorts of absorbents. Some will absorb only oil from the water, then you can actually re-use them (not that I would). Try the bent turkey pan thing before spending a pile on some custom pan.

Paraphrased from "Keep Your Marine Diesel Running" by Richard Thiel:
  • Must have engine hour meter.
  • Keep log of all engine events: add/change oil, repairs, estimated fuel mileage during trips.
  • Single-viscosity oil is preferable. Use higher viscosity in hot climates.
  • Want automatic alarm when too much water in fuel/water separator.
  • If boat unused for more than 1 month, add fuel stabilizer to tank.
  • Want transparent coolant recovery bottle.

From Captain Hugenot of SFSailing:
... let the engine run without load for five minutes prior to each shut down so that the engine can cool down ... Letting it cool for five minutes prevents the build up of salt deposits in the water jacket. If you shut it down hot, the salt water sitting in the jacket boils and precipitates all the salt on the cast iron causing more rapid corrosion. If you properly cool the engine this is prevented. ...

Engine compartment:
  • Want separate compartments for engine and batteries because temperature affects batteries.

  • Put handholds inside engine compartment so you can reach remote parts of engine without having to lean on it, can work on engine at sea without being thrown onto it.
    Non-skid or foot-railings in strategic places.
    Good work-lights.
    A fan to keep you comfortable while working.

  • From "Modern Boat Maintenance" edited by Bo Streiffert:
    Consider adding an extra air intake vent to the engine compartment; many boats have too small a vent, and starve the engine a bit.
    (But from Pat Manley: "If your engine produces no black smoke at full RPM under full load, i.e. full RPM at maximum boat speed in calm water, it's getting enough air.")
    (Try opening hatch to compartment while engine is running; if engine speeds up, air vent is too small.)

  • Get automatic fire-extinguisher for engine/battery compartment.

  • Want way to plug engine compartment air vents quickly from outside in case of fire.

  • Small fire extinguisher port in side of engine compartment, so you can fight fire without opening whole compartment.

  • Make sure all equipment in the compartment is mounted solidly; for example, some people have found that their gensets weren't.

Don Casey's "Engine-compartment Fan"

From JAX on Cruising World message board:
... Engine oil gets acidic from use, diesel engine oil particularly more so. Leaving used oil in an engine for a period of time will etch the bearings. That's why oil is changed before fall layup.

Pascoe says an engine lasts ten years, without regard to hours used. He says a marine engine dies from corrosion.

My experience is now and always has been that people who change their oil frequently (and use the best quality oil) get WAY more hours (200% to 300% to 400% more hours/miles) before the engine is junk. Oil is cheap. Engines aren't.

Pre-lubrication (to establish oil pressure before engine starts):
From JAX on Cruising World message board:
... it can take upwards of ten to twenty seconds after startup for oil to get all the places that need oil. The bearings and piston faces are most vulnerable, but there are also lots of other surfaces that need fresh oil.

However, it is not necessary to install a pre-lube system. All you have to do is spin the engine over with the fuel-stop pulled (or on a gas engine push the throttle forward enough so the engine won't start) long enough for the oil pressure to come up, plus about 5 to 10 seconds more.

There are people who seem to know what they are talking about who claim 50% to 80% of engine wear occurs due to oil starvation at startup. Also, expensive high-performance race engines are nearly always spun up with an aux starter with the ignition off until oil pressure has been established. ...

From John / Truelove on The Live-Aboard List:
> "They say" 80% of the wear happens in the first few seconds of operation due to dry bearings.

Yes, they do, and yes it does. But it isn't due to "dry bearings." It's due to metal-to-metal contact between bearing surfaces before the hydrodynamic "wedge" develops. The wedge is developed by virtue of the bearing surfaces moving in relation to each other. It is not developed by pressurizing the lubeoil system prior to start, and the same amount of wear will occur during starting whether there is pressurized oil at the bearing journals or not. Prelube pumps are a good idea on large engines which require a lot of time to fill their oil distribution and filtration systems, and also on infrequently-run engines such as those powering standby generators. They are a waste of money on small, frequently-operated Diesels.


"Installing Engine Monitor Gauges" by Jan Mundy in issue 2000 #2 of DIY Boat Owner magazine

From Jeff H on Cruising World message board:
The current Yanmar line is really a pain in the butt in that you almost have to end up with a turbo-charged engine in the bigger HP ratings. I really think that putting a turbo-charged engine in a sailboat is a major mistake. The way we use engines is the dead wrong way to use a turbo and so the engines experience turbo problems in rather short order. Once the turbo starts to go you can quickly do damage to the engine itself.


Turbo chargers are great for powerboats that spend much of their lives operating at near full throttle but the way that sailors often use engines is the dead wrong way to use a turbo (idling at bridges, charging batteries, motoring below cruising speed) and so the engines experience turbo problems in rather short order. Once the turbo starts to go you can quickly do damage to the engine itself. I have watched this on a couple boats and while careful skippers can get reasonable life out of a turbo, I would never buy a boat that had one and given the choice would never put one in.
From TomC on Cruising World message board:
I wouldn't go turbo. Not on a 20,000 pound boat. There are small bearings, issues with cooling down, another potential sensitive area for corrosion, and added space requirements to deal with. ...
From Mark on Cruising World message board:
Having spent many years as a heavy equip mechanic in the military I have seen it all. Personally a turbo would never go in my boat. Un-needed complexity, extra heat, extra RPM, extra cost. And from what I've been reading on this BB nobody can find a marine mechanic much less a turbo mechanic. ...

From "Offshore Cruising Encyclopedia" (1989) by Steve and Linda Dashew:
When buying a new engine:
  • To help size the engine, consult owners of sisterships.
  • Keep an eye on boat resale value: will future buyers approve of your choice ?
  • Extra power can help you avoid expensive accidents.
  • Having the factory "detune" an engine to decrease HP and top RPM can give more low-end torque, lower fuel consumption, and longer life.
  • An intercooler (cools the incoming air) can increase HP by 10 percent with almost no increase in fuel consumption.

Lifetime until overhaul:
From Pascal on BoaterEd forum:
Money saving tip : never never never never never overload diesel engines (make sure they turn rated RPM at WOT with full tanks and gear) and never never never never let them run hot.

From Bruce on BoaterEd forum:
Be certain your engines can reach RPM above rated MAX rated HP RPM, if they can't they are overloaded and will die young.

Learn to read and understand the MFG. specs for duty cycle and performance ratings. If your mechanic or salesman doesn't know the duty cycle rating he doesn't know what he is talking about.

Don't listen to "diesel myths" such as "run them hard, 200 rpm off the top" for best life. That baloney only applied, if then, to 120 HP to NA Detroit's because they were way underrated by today's HP standards. If you want good life don't run at 50 or more HP per LTR ratings instead run at 30 HP/LTr and certainly not 200 off the top. Every diesel engine of any design wears out based on fuel use, which equals work performed in (HP hours) independent of hours of operation. Fuel use directly equates to work performed as 4-strokes will produce about 20 HP per hour per gallon of fuel. Run them at 50-60 HP/Ltr and you will get 1-2K hours; at 30 HP they will outlive you.

Pleasure-use diesels rarely wear out unless overworked. They die from the results of poor maintenance such as overheating.

From Viveiros on BoaterEd forum:
Unfortunately, it's not a "rarity" to see newer diesel boats have major engine issues at relatively short running hours - such as in hundreds of hours. Many (like me) are of the mindset that the majority of these early issues are not truly engine reliabilty or longevity issues. I'm sure some are, but most are arguably related to installation and/or application. The posts above about overloading and RPM are SO important and all too often, completely ignored by operators and manufacturers alike. The result can be premature failure and lots of expense.

Having said that, a "properly" setup diesel vessel with a conscientious operator can have a lot more than 15 years of service from a good set of engines. My engines are of 1989 vintage and have never been apart. They still run quite well and I don't expect to have to overhaul them any time soon. Most engine manufacturers don't rate the life of their engines in years or even hours of use. They loosely rate them by a measure of gallons of fuel burned prior to overhaul. Even that is not a perfect measure as some go more and some less depending on so many factors.

When buying, there are some things I would look for to guard against a potentially expensive mistake. ... Don't trust that because a boats newer, or has fewer hours, that it is mechanically superior to another vessel. Engine damage can happen regardless of age or hours and can happen in minutes. Don't trust that the boat manufacturer got the boat setup right for reliability or longevity. All too often, they set boats up to generate impressive magazine review numbers. These same setups, can fail miserably once the boats get to the end user and the bottoms are painted, enclosures added and the weight climbs into a more realistsic number. At this point, the engines ARE overloaded and damage is quite possible, even likely. Even if you're "good" mechanically, interview and hire the best diesel tech you can find - preferably brand-specific to the engines ... Lastly, look for boats that have been setup and run since new by a really conscientious owner. Seeing aftermarket boost gages and pyrometers at the helm and knowing that the captain understands them (and has had them since new) is a huge positive in my book.

From Lew Hodgett on the Yacht-L mailing list:
> I'm about to fork out A$188 for a single injector nozzle for
> my Volvo twin (spring A$78, washer A$34 if needed), but rang
> a diesel injection supplier and asked price for nozzle for "my" Kubota
> tractor D-850 - his reply? "Don't carry nozzles, but a new complete
> injector is $31, including GST"!

One of the basic reasons I would never consider purchase of a Volvo.

The other being unusually long delivery cycles for parts, at least that has been the experience of several people I've known.

If I were looking at a boat that contained a Volvo, would discount my best offer by at least $7,500 just to cover the aggravation factor of the bloody Volvo.

From Rick Kennerly on The Live-Aboard List:
A lot of Westsail 32s came with either Volvos MD2B or MD2030 or Perkins 4-107(8)s. The rule of thumb in the WOA is to subtract several thousand dollars from the price if purchasing a boat with a Volvo and add several thousand for a Perkins (or now Yanmar or Universal, if a recent repower).

Volvo parts are difficult to get and expensive, very. Most have raw water cooling. There is a guy locally here in Annapolis who spent tons of money rebuilding his Volvo 20 year old MD2B since he had to open it up anyway because of a water leak anyway. A few months after he was finished, the engine sprang more pin hole leaks.

From Chris Ruck on The Live-Aboard List:
I have a 1986 Volvo 2003. I have just had an engine rebuild (engine goes back in on Monday). Engine hours were 1830 or so. The compression went which was why the rebuild. Don't know what it is going to cost!! Except that parts are very expensive, some having to come from Sweden. From 1991 to 1999 went like a dream and then slowly had more and more difficulty starting it. In the end, when cold, I was starting it on 1 cylinder and then flipping the lever to 3 cylinders. No problem but a tad inconvenient!! As the stairs had to be removed each time!

Noise and Vibration, from article by Steve D'Antonio in 5/2002 issue of PassageMaker magazine:
  • Rumbles and buzzes: usually propeller blade rotation rate, exhaust system, engine mounts, engine air intake, charger/inverter.
  • Growl or whine: usually hydraulics, exhaust, propeller.
  • Roar or singing: usually propeller, or gear tooth resonation.
  • Very high-frequency: turbocharger.
  • Rattles: often engine mounts, engine bed stringers, propeller imbalance.
  • Shudders: usually hydrodynamic: waves, or rudder/fin/keel movement.
  • Wiggles: usually engine mounts, engine bed stringers, prop shaft imbalance.
Experiment to find sources.
Frequency often is a good clue.

See my Boat Engine Maintenance page.
See Tools section of my Boat Maintenance page for engine tools.
Electric motor as main engine:
Requires huge battery bank, and is hard on batteries (have to replace them every couple of years).

Elco Electric Launch. "... they've done repower for small sailboats. I inquired about repowering my 40 foot steel hulled yawl, and THAT was not practical."

Lynch Motor
GreenStar Marine E-Line
VETUS Electric Propulsion

Solomon Technologies (see article in 12/2001 issue of Practical Sailor)

From Dan on Latitudes and Attitudes Cruisers Forum 9/2006:
I got an estimate from Solomon Industries to convert my catamaran over to electric propulsion. Are you ready for this? $27,061.

That is just to buy it, not installed. [Also doesn't include shipping, sales tax or import duties, I think.] It is also with the smallest amp hour battery pack, smallest gen set that they offer. Of course you can upgrade it as options.

Picking major items out of the price list he gave:
Twin 6 HP motors: $14,700
Power management panel $1,300
Electronic throttle system $800
Battery cables $1,300
Battery charger (144 VDC) $1,900
DC/DC charger/converter $900
Main distribution box $2,000
Solar charge controller (1000W) would be $1,000 [not added to quote]
Inverter (3 KW, 144 VDC to 110 VAC) would be $3,000 [not added to quote]
Batteries (12 AGM group 24, 80 AH each) $2,500
(I don't see a genset in the quote; that would be additional to the $27K, I think.]

From SoItGoes on Latitudes and Attitudes Cruisers Forum 9/2006:
I converted our CAL 34 to electric drive a couple years back and it works a lot better than the old Atomic 4 (may it rest in peace ...) ...

The electric motor, extra batteries and all wound up weighing in about 150 pounds less than the old engine and that includes the spare motor we keep in a locker.

One of the nice things about electric drive is that all of the components are available off the shelf for the golf cart industry so quite cheap if you use your head and avoid the snake oil folk trying to resell the same stuff as "marine" for ten times as much.

Total cost of our system was just over $1500. ThunderStruck has a kit for $980.

From slrman on Latitudes and Attitudes Cruisers Forum 9/2006:
Solomon industries is way overpriced and over-engineered to justify it. As mentioned above, this conversion can be done much more easily with off-the shelf components.

Outboard Motor     Sparkplug firing

Outboard motor characteristics:
Cycle type:
  • 2-Stroke: cycle consists of 2 strokes by piston:
    up is exhaust/compression stroke,
    down is power/intake stroke.

  • 4-Stroke: cycle consists of 4 strokes by piston:
    up for compression stroke,
    down for power stroke.
    up for exhaust stroke,
    down for intake stroke.
4-stroke design uses valves, separate lubrication system.
2-stroke design uses cylinder ports, oil mixed into fuel.

2-stroke gives more power for same weight, but consumes more fuel and generates more pollution and noise, has less low-end torque.

Fuel system type:
  • Carbureted: air is sucked through a venturi, gas is sucked in to mix with it, then mixture goes to cylinder.
    May be one single-barrel carburetor per cylinder, or one two-barrel per two cylinders.

  • Fuel-injected: fuel is sprayed into cylinder, or chamber that feeds to cylinder. Mixes with air in the cylinder.
    May be single-point or multi-point injection. May be electronic (injects into intake manifold) or direct (injects into cylinder; better).
Most small 2-stroke outboards use carburetors.

Ignition system type:
  • Flywheel magneto with breaker points.
  • Flywheel magneto without breaker points (aka "solid-state").
  • Capacitor discharge. Gives higher voltage.
Note: spark plugs are not properly gapped when you buy them; you have to set the gap.

Engine cooling system type:
  • Water-cooled.
  • Air-cooled. Noisy.
Some Honda's have water-cooled propeller shaft but air-cooled engine.

  • Electric-start or manual pull-start ?
  • DC output (useful for running navigation lights) ?
  • Shaft length.
  • Internal or external fuel tank ?
  • Weight.
  • Horsepower.

15-HP outboards tested in article by Ed Sherman in 10/2003 issue of Cruising World magazine

According to John Neal, as of 2/2000:
4-stroke outboard technology is not quite "mature" yet.

4-stroke outboard is about 40% heavier than equivalent 2-stroke.
Typical 9.9 HP motor: 2-stroke == 75 lb, 4-stroke == more than 100 lb.

From 8-HP 4-stroke test article in 1/15/2004 issue of Practical Sailor:
Dinghy capacity rating plates typically specify maximum HP, but not maximum weight of the motor. A 4-stroke may satisfy the HP limit but still be too heavy for the dinghy, causing squatting and bucking.

From Pat Manley: "Fuel consumption of 4-strokes is about half that of the equivalent 2-stroke, they are less 'smokey' and have negligible oil consumption. Ecologically I don't think there is any doubt which is the better. Many people consider their exhaust note much less intrusive."

4-stroke outboard parts are hard to get outside the USA.

From Daniel Todd on Yacht-L mailing list, 6/2001:
... Thanks to the incredible foresight of the California State legislature, it is illegal to sell 2-stroke outboards in the state as of January 1st. ...

Met someone at St Michaels MD in 7/2002 who was cursing his brand-new Yamaha 4-stroke (looked like about 6 HP), which wouldn't start: said it always was balky to start, vibrated badly, often broke down.

From letter by Raymond McCall in 9/2002 issue of BoatU.S. magazine:
... A two-stroke has 3 moving parts per cylinder. The four-stroke has 27. ... Tilt your two-stroke and nothing happens. Tilt the four-stroke and the oil is not where it belongs any more. ... the oil in the two-stroke coats the cylinders. The four-stroke cylinders do not have this oil coating and will rust when not run for long periods ...

Sailnet - Tom Wood's "The Great Stroke Debate"
8-HP 4-stroke test article in 1/15/2004 issue of Practical Sailor

From Sv Feng Shui on SSCA discussion boards 2/2001:
If you are planning a cruise outside of the USA be forewarned - 4-stroke outboards are rare outside of the US, Canada, Japan, and parts of Europe. I was told last week when my 9.9 Yamaha 4-stroke failed after only 17 months that I would need to return it to the US for authorized service. No place south of Puerto Rico will repair a 4-stroke and if someone does the Yamaha warranty is void. Also be aware that Yamaha requires a fresh water flush of the engine after EACH use in salt water - or the warranty is void.

Yamaha outboards: my understanding is that Yamaha enforces a separation between motors sold in USA, and those sold outside USA (Enduro brand). If you buy a motor in one place and take it to the other, you can't get parts for it. This seems like a good reason not to buy Yamaha.

From Rob on "Mattkare" 11/2006:
The Asian-built Yamaha he bought 10 years ago was great.

The French-built Yamaha 4-stroke 4-HP or 6-HP he bought in 2005 is terrible:
  • Has some intermittent backfiring-upon-starting problem that has shattered part of the cowling by slamming the handle into it, and Yamaha refuses to cover under warranty (they say cowling is not part of the motor, thus not covered). Dealer can't even fix it; they say nothing is wrong, even though he managed to make the problem happen right in front of them.
  • A Yamaha dealer told him that they'd had to double their stocks of spare parts to handle all the problems with the new French-built motors.
  • Hose from impeller up to block rotted in 1.5 years.
  • Design and materials are crap; for example, cowling is some kind of weak plastic instead of fiberglass.
  • Hard to pull; takes a lot of force to start, and wife can barely do it.

My experience:
I bought a 4-stroke Tohatsu 6 HP in 3/2008:
  • It purrs at idle, but in gear it runs louder and with more vibration than I expected. I guess that's what you get with a 1-cylinder motor. But I didn't want the weight-penalty of a 2-cylinder motor.

  • It really wants the choke knob out for starting, even when warm.

  • Dealer told me to grease the transom-attachment-bolts, to keep them from getting frozen.

  • Within a month or so, a few minor parts are showing rust: the cosmetic metal on the pull-start-handle, and the tilt-up support.

  • The motor uses very little gasoline; it's amazing after using an old 2-stroke 20 HP.

  • 6 HP not enough to plane a heavy RIB with 220-pound me in it.

From Ralph Caruso on World-Cruising mailing list 9/2008:
I have a Honda 8, which I purchased in 2000, and would recommend against buying one in the future. Parts are difficult to find, because dealers are few and far between, and they do not carry much stock, and it is difficult to get good service from them for dinghy motors. I think they may give decent service for the larger motors, but I had real difficulty getting parts in Stuart Florida for my motor. There was only one dealer in Annapolis MD, one of the major east-coast sailing centers, and their service was horrible. Cost of parts and service is also high. I am not confident of my ability to find parts here in France, now that I am here.


[Some Honda dealers handle only large motors; some don't stock parts for many motors.]

[Hesitation problem on Honda 8 figured out:] when Viking had done their tuneup, they had left off one of the two mounting bolts for the ignition coil. This is a 2-cylinder engine, and each bolt is a ground for one cylinder. With one bolt missing, that plug was getting spark only intermittently, and not often enough at high revs. Over time, the other bolt backed out more and more, and the problem got worse. The reason the bolt was missing was that the Honda "engineers" who designed this engine used a blind pocket for the nut for the bolt, which is impossible to access without taking apart a LOT of the engine. ...

Unfortunately, it is very difficult for the normal boater to order Honda parts over the web. Honda does not publish lists of parts on the web, with engine diagrams, like Yamaha and other manufacturers do, and the dealers do not sell over the web. I found one site that did, but it was not quite clear whether the parts they were selling were for my engine, so I did not want to take the chance.

I owned a Honda (actually an Acura) auto for nearly 15 years, and found the same issues there - engineering that does not take maintainability into account, and parts/dealer networks that limit availability to drive up prices. The Acura blower fan had a failure of the blower motor bearing (a 50 cent part) that required the removal of the entire dashboard and almost EVERYTHING underneath it to replace - the dealer wanted $1400 to do this job. I found a web site that showed how to DIY, and I did it over two whole days of taking the interior apart. The distributor cap on the same car was notoriously difficult to remove and service.

I will never buy a Honda product again, because of these experiences. I am an engineer, and although they produce some good products, they are not worth the aggravation.

From John Dunsmoor:
[Re: decarbonizing a dinghy's outboard motor:]

Two-strokes, new ones with 50 to 1 oil and run hard aren't going to have carbon as their problem. I would say the main reason outboards die is corrosion and electrical problems, more corrosion.

They just are not built in a way to survive the environment they live in.

If I was going to design an outboard for sea service it would probably be made out of carbon fiber with everything else 316 or 18-8 stainless. All the electronics would be epoxy encapsulated and the whole thing would cost one-third of what outboards cost today.

I was buying Johnson's on the international market, a special workhorse engine that was made for export only and the price was half what we pay for outboards here in the US ... WHY ?

I have opened up outboards with thousands of hours of use, and carbon is not usually a problem.

From Gary Elder:
As a matter of routine, when my outboard gas gets to be about a month old, I dump it into the car gas tank, then fill it up - never a problem.

Propeller stores:
Advantage Discount Propellers, 888-757-7767

Good idea: propeller guard.

Used parts:
Marine Parts Outlet

Laing's Outboard Motors

Used motors:
Used outboards on
Used outboards at AFA Marine

See my Outboard Motor Maintenance page.

Torqeedo electric outboard (about $1600; battery exchange $600; power equivalent to 2 HP gasoline outboard; dinghy range on a single charge only 2.5 NM at 4 knots).