The Offshore Voyaging Reference Site

Perkins M92B, Initial Report Card


We have long believed that the prevalence of high revving lightly built engines installed in sailboats, particularly those boats built in recent years, is often more about ease of availability to the builder and initial price than making the best choice to give long term economical service to the owner. Particularly an owner, like many of our readers, who either does, or plans to, put a lot of miles on.

Regular readers of this site will remember that back in the spring we posted several articles about our re-power engine selection process and final decision to install a Perkins M92B.

Now that we have some hours on the new engine we are seeing some real benefits that, at least initially, are making us happy that we took a different path, opting for a slow revving (2400 top end) high torque industrial engine of lower horsepower than would generally be specified for a boat the size of Morgan’s Cloud.

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Matt Marsh

Thanks for this post, John. Your experience seems to confirm what I keep hearing from long-distance voyagers, big ship guys and maintenance engineers- a solid, medium-RPM industrial/marine duty engine is the ideal match to typical displacement hulls.

A lot of what shows up in the marine engine market really seems to be light-duty car and utility motors, modified slightly to meet marine requirements, and turbocharged / ECU-mapped to within an inch of their lives. A rather extreme but interesting comparison at the 600 hp point is the 81 litre Grenaa six-cylinder compared to 12-13 L turbo six-cylinders based on truck blocks. (A friend who’s thinking of building a large motor passagemaker has been posting in detail about this on lately.) The Grenaa costs much more and is far heavier- but in a boat that’s designed to handle its bulk, the Grenaa will run with significantly better fuel efficiency, needing only routine maintenance, through the truck-engined boat’s first four repowers.

Obviously an 81 litre, 8-tonne engine at 600 rpm is an extreme example, but the principle is clear: a larger, slower, less highly loaded engine tends to be longer lived, more reliable, more fuel efficient, and- for several reasons- easier to coax into compliance with emissions laws.

Pete Worrell

Thanks for this good input. Sensible. We have found that propeller selection may be just as challenging as motor selection. I have mentioned this before, but I have had great experience with the AUTOPROP, a self pitching propeller made by Bruntons UK and imported to USA by AB Marine. It continually finds the correct efficient pitch depending upon load and speed, and we have really benefited from it (especially when motor sailing, you get a puff, the propeller changes pitch and off you go). Feathers when unused as long as shaft is stopped. Have heard very good things about the folding Gori’s as well.

Pete & Kareen Worrell

Pete Worrell


I agree, I have heard of some problems years ago with the Autoprop, including one or two that threw a blade. I have heard also from some people that they thought that the Autoprop was noisier or vibrated more than other props, but I haven’t had that issue. I do know that it is critical that the prop be fitted specifically to your vessel/power combination and AB Marine did physically install my prop. I agree that a hydraulic transmission adds a complexity with the need for a shaft lock. And as we all know, complexity=bad; simplicity=good!

Pete & Kareen

Martin Wright


If it is any comfort, I re-engined a Bowman 48 with a Perkins M92B, and I have been very pleased with it. There have been only two annoyances: The welds for the water injection cowl on the stainless steel exhaust swan neck failed – poor quality control, and the cooling system is sensitive to being even slightly overfilled.

Overall, I think that it is a good choice – I hope so – as i have plans for going to high latitudes once children are through school!

Thank you for a great website.

Martin Wright

Doug Bruce

As further evidence of the benefits of a slow revving engine, our 24 year old Perkins TC 6.534 which has max revs of 2500 is still running very well with just under 7000 hours, and our diesel mechanics all say she’s got lots of life left. I hope they are right! These same mechanics also confirm they see many more problems with light weight high revving “screamers” as you call them.

Conny Harlin

Hi John & Phyllis.
Regarding fuel consumption, of course the match of prop (especially the diameter to get grip) is crucial to what torque and power your engine delivers. But the key in fuel consumption is the RPM. The revs have an impact of ~70% on fuel consumption on a given engine. Tuning, timing, trimming, polishing, air/fuel distribution, etc., can only make an impact of ~30% when it comes to fuel consumption. There is a reason why ocean vessels, fishing boats, run on low rpm.

I did a test in the past at work, and drove a car up a given grade (fully instrumented for fuel measuring). The test was to keep a constant speed of 70 km/h in both runs. First test was on 4th gear, which was easy on part load to hold 70 km/h. The second was on top gear and I had to nail that pedal (full throttle) all the way to the top to maintain 70 km/h… Guess what consumed less fuel??? The second due to lower RPM. Not the first one (with only 70% throttle). The reason was that the RPM was several hundred less. The worst gas-guzzlers I know in this world are those high rev chain saws and leaf-blowers.

Conclusion, always go low RPM if you wanna save fuel.

Congratulations on your choice of a non high rev Perkins engine.

Conny Harlin

Hi again John.

I forgot a comment in my previous comment.

If the objective is to save fuel with a combustion engine, always ride on max torque, not max power, which gains at max RPM. Always study your engine’s torque and max power curve and make your decision and matching of prop after that. On my sailboat I cannot reach max power (250 rpm less) due to my lay-out of prop (large diameter and excellent grip in the media water). Who cares, I can only make my 6,5 – 7,0 knots anyway and I get it at 1600-1700 rpm (800 rpm below max power). But my fuel consumption makes me happy. I have an old engine from the 70s with max rpm of 2400 rpm. Today’s modern engines usually run over 3000 rpm and are often turbo charged in order to make an engine light and small with high output. Keep in mind that every other time (four stroke) a piston comes to top dead end it has to be fed with fuel.

So long, hope to meet you guys on the water sometime in the future.

Nick Kats

First, I have to say that I’m quite ignorant about engines & props. I just service what I have, though a bit grudgingly.

Mine is a 1965 Sabb 30 hp diesel, the old fashioned kind with massive flywheel. This for a 15 ton, 39′ LOD ketch. For this size, 75-150 HP is more like the norm in Norway.

But in sheltered waters this Sabb will drive the boat directly upwind in 35 knots, though not 40. This is more than adequate. In calm, 6 knots at modest RPMs.

So, a small engine for a big sailboat is just fine. If it is windy, sail & don’t motor, if calm, a small engine will do 4 or 5 knots, if in between, motorsail. So, a smaller engine seems to me to be better.

Second, the Sabb has a hand starter. I’ve used it quite a few x. If I’m fit, I can do it, if not, I have to get really psyched up, have a cuppa coffee, maybe hyperventilate a bit. And I’m 52 & not getting younger…

If I had my dibs, I would go down to a smaller engine, say 15 or 20 HP. Then handstarting would be a cinch.

Third, on the times I could not handstart but needed to move, got into my 8′ hard rowboat & towed the ketch. Take 10 minutes to get her up to speed, 1 knot. Useful to have this ability.

Which means that manning a sweep from the cockpit will do just as well.

Which makes an engine even less necessary (unless you sail weekends & work weeks).

Which brings me to my real feelings about engines on my sailboat. I used to roam the Maine coast for weeks in a 21′ yawl. Always removed the outboard. Had oars, so no problem to row in calms. I found that without the outboard instantly I was a far better sailor, and that I learned exponentially. Also, when I got back to having a motor on a sailboat, my sailing abilities relapsed back to ‘normal’. Huge difference. I have always resented engines for taking away this edge from me, of an absolutely superlative state of mind re sailing.

I would say that the Pardeys got it right, sailing without engines.

Nick Kats
39′ Colin Archer ketch


I also installed a M92-B. Just passed the 100 hour mark. One of the things I noticed when I was looking was that there are few to none that are naturally aspirated at this size or smaller. Turbo charging does several things, smaller, lighter, faster revving, but more significantly in the US at any rate, is that they are cleaner burning. The enviromental trend will lead to more complex electronic controls and turbos on all motors in the not too distant future. Not necessarily the simple reliable solution.

Question: With all the electrical items on the M92-B have you thought about what a lightning strike would do? How would you deal with it after a hit? Getting the engine running?


pete & sally

If you want to get the best out of the engine use MOLYSLIP in the oil. We have been using it for over 20 years and have been reaping the benefit of low fuel costs better running and NO smoking and our engine is an old 3.8 ltr 4 cylinder 65hp Thornicroft thumper (max2400) that has now done 14000hrs and people can’t believe it still doesn’t smoke.


Since you mention Beta Marine, what do you think are the benfits with the Perkins engine compared to the Beta 90? I am curious since I am choosing between them.


We have had an Autoprop on our sailboat for 10 years and have serviced it yearly as required. It just lost a blade and caused considerable damage to our shaft. We have just learned that there was a recall on the prop but were not notified. We have been trying to get some satisfaction from Bruton and AB Marine but so far have been unsuccessful. I do not think that there are only a few instances of blades being lost. We have met at least three other sailors who also lost a blade and if you check the internet you will see others. It works great but beware of blade loss even when properly maintained.

guy blanchet

I’m doing the same process than you. With experience would you do the sames choices? Until now, I thing to put on my Corbin 39 the M92-B with ZF45-1 continuous duty 2:1 transmission, a Balmar AT-200 alternator with MC-614 regulator, 4 or 6 Trojan Premium Line deep-cycle flooded 16RE-B 6v batteries with single point watering system for a 740 ou 1110 amps bank, an Autoprop or Maxprop propeller. What do you think; anything else to consider; any comment or suggestion appreciated.

Marc Dacey

I concur completely with John: You’ve specified a nice set up for a 55-60 foot full keeler there. The Beta 43 is a far better choice.

By way of illustration, I worked my way backwards from the assumption that the diesel would be “happiest” (and the owner with the fuel consumption ratios) if I could motor cruise at about 75% output. I determined that a Beta 60 driving a (fully loaded) 16 tonne steel full keeler and turning a 19 x 15 (nominal) four-bladed Variprop via a ZF-25A 1.98: 1 hydraulic transmission would suit us fine, would fit the existing bay, and would leave enough leeway to run a pair of 90-110 amp alternators from a double PTO. This would provide juice to a very similar bank of six L16 batteries, although I am coming to think of Trojans as a little overrated…I still like the L16 form factor.

What I have is “right-sized” for our use, and the fuel economy is better than the slightly less powerful engine it replaced, so there’s no hit there due to the HP uptick. The previous engine was a Westerbeke 52 HP turning a slightly smaller fixed three-blade prop…and it was fine as well. Your boat is about ten thousand pounds lighter than ours…puting in an 87 HP is like dropping a Chevy 427 block into a Vega in the ’70s. I’ve seen it done, but the results were in no sense satisfactory! Forty to 45 HP with a properly pitched prop is fine…maybe 50 HP if you have the heaviest Corbin 39, the full pilothouse version, which according to Yachtworld runs about 26,000 lbs.


I Marc,
Thank’s for this very helpfull info. I have the pilothouse ketch, so the 50 or maebe the 60 HP like Beta suggested me today for extra power.
Why do you prefer 2 X 110 amp alternators? Are 2 Balmars ok or those included with the Beta package would be so good?
Do you prefer an other brand than Trojan?
Is the Variprop preferable, why?


Hi John,
Thank’s, it’s really helpfull.
What about the batteries and the prop?
Do you prefer 2 smaller alternators to a bigger one?
Is the Beta also a strong, low rpm engine with long expected life like Perkins or more a smal high rpm shorter life one like Yanmar?

Herb Bondurant

It’s always about the money;that’s why we love sailing

Bill Koppe

Hi John,
I have bought a new Perkins 215C and note it has no zinc anodes, despite a heat exchanger and mixtures of copper , brass and aluminium in the saltwater circuit. Having had Perkins 6354 and Prima in previous yachts which corroded the watercooled exhaust 3 times in the 6354 over 20 years.
Ifeel that this is a future problem and will now convert to keel cooling but using a separate large heat exchanger instead of the keel cooler.
Have you considered this issue on your Perkins?
The cast iron ones lasted far longer than the aluminium ones


Tks John, most interesting line of arguments regarding the choice of engine. I also know that watercooling requires a considerable amount of engineering and equipment on and after the engine and sooner or later leakages or worn out pipes, houses and valves need attention. A possible solution you have not touched is the air cooled engine in the same power range (like the Deuz 912). These engines respond to the same general criteria like low rev, low consumption high torque, solid build etc. Of course there would be some plumbing required for air ducts (which could be used for heating the living area) but I feel that the simplicity of application as you always and rightly propose would be well met with air cooling. Do you have a view on this?



Please share with me which engines are rumored to be designed for 3-4K hours?

Eric Klem

Hi Dominic,

There are many things that can kill an engine like bearings, corrosion, parts availability etc but the most common that I know of on a properly maintained engine is simply ring wear. Ring wear can be approximated with a “PV” relationship where P is pressure between the ring and the cylinder wall and V is velocity. The harder you run an engine, the higher the cylinder pressure (cylinder pressure is basically torque) and the rings are designed so that this cylinder pressure gets in behind them and pushes them against the cylinder wall to seal. In the old days, the rule of thumb for ring speed was 6 m/s for a long lasting ring but many engines exceed that these days. Note that this is a linear speed so a short stroke engine can be higher rpm for the same ring speed. As you can see, running hard and running fast both contribute to this wear which leads to lower compression and the engine “wearing out”. In old cars, you may remember oil pressure was another sign and that was due to the clearances opening up in plain bearings but that is not really an issue anymore.



I understand that these are rumors. Multiple documented early rebuilds on well maintained engines would be more than rumors.

Yanmar is a builder of higher reving marine diesel engines. Is there any history of Yammers wearing their rings early due to the higher rpms? Any rumors? I speaking of their very common 4jh series.

Is anyone getting 10K hours out of them?