Air Cooled, Enclosed, Marine Gen Sets

Our 1977 7.5 Kohler gen set is aged. May need to replace.

Before I google - wonder if some on TF may have brand recommendation:

Marine air cooled genset that can be permanently placed in an enclosed engine compartment

I imagine that ingress and egress fan-forced air cooling and exterior exhaust systems can be designed. If not available - why not?

Thanks for any suggestions!

This is from Northern Lights brochure on choosing a marine generator. I also suspect that air cooled gensets are not ignition protected if you are using gas instead of diesel.

Direct seawater cooling systems pump seawater through the engine. Corrosion and system contamination problems make direct cooling systems unsuitable for most marine applications. Air cooled generator engines exist, but they are not intended for use in a marine environment.

Hey Art,

On larger boats, I've seen people install smaller ones on the forward deck, not in an enclosed space. Basically, they treated it like an outdoor install at home.

My former boat, a 1977 Californian 42' LRC had a Kohler 7.5 power plant specifically:

7.5RC0P23
Serial No.: 414213
Drawing No.: 10527B
Controller Model: D-246974

It was infinitely fixable. The engine was a Perkins 4.107, which is almost the same as a 4.108. It is a common sailboat engine with full parts availability and fully rebuildable.

Marine cooling components were available from Perkins dealers and others, e.g S&W, TAD, and MrCool.us.

The genset rotor and stator were straightforward and rewindable at an electrical shop. And, brushes were available.

The controller was very basic with resistors and relays and the like that had substitutes that could be bought from places like Digikey and Newark.

The charge circuit was old school, not smart, and basically burned off voltage above a threshold on a huge resistor. I just left it off and let the generator supply AC power to the same charger used on shore power.

It was basically droop regulation of voltage and frequency, tunes at the engine low speed (idle) governor and a variable field resistor, but it worked surprisingly well.

It had water temp, oil pressure, no/low output, and overcrank protection.

I'm happy to try to help if you are having a problem with it. And, there are folks at SmokeStak that know those things better than the dealers of the day! Many of the controller schematics can be having the forums there or from their resident smart folks.

At any rate, you may want to replace yours, and it may be different than mine, but if I can help, please post or DM.

What is it doing (or not) to you?

To your question, one can have a dry stack for a marine genset, just like one can have a dry stack for a marine engine. There have been a bunch of threads about that.

See the usual about the stack going up and out through the saloon or galley, noise, birds, etc.

You tend to see them on workboats more than pleasure craft, and installation is more involved, more expensive, and comes with more compromises than it may initially seem.

gkesden said:

To your question, one can have a dry stack for a marine genset, just like one can have a dry stack for a marine engine. There have been a bunch of threads about that.

See the usual about the stack going up and out through the saloon or galley, noise, birds, etc.

You tend to see them on workboats more than pleasure craft, and installation is more involved, more expensive, and comes with more compromises than it may initially seem.

Click to expand...

Dry stack is still water cooled, but a keel cooler instead of wet exhaust. Notably, Nordhavn uses wet exhaust on their dry-stack boats.

An air cooled diesel generator will be LOUD. Air is a much less efficient heat transfer medium compared to fluid, so the physical apertures will need to be much larger (100 sq in vent vs 1.5" thru hull).

Your current generator is air cooled? I'm surprised. Didn't know there were permanently installed air cooled marine generators, at least in the US. I've seen some oddball air cooled diesels in other parts of the world, but mainstream.

Curious to know what problem you're solving. Punching a thru-hull is pretty straightforward. Small gear driven water pump on a generator is more reliable than a large Delta blower and ducting.

Peter

Used to have a lister 3 cylinder air cooled genset on one of the landing crafts I worked on. It was loud and made a lot of extra heat in the engine room. It's purpose was to be able to still have power when beached.

Art,
Are you referring to the rotor/ windings being air cooled? This is more common and does have ventilation requirements.

Air cooled would only work for deck mounted work boats. I can’t see any other application. Installed on a P/V would be a disaster

You can make anything work with enough engineering, question becomes are the compromises worth it?
I assume the goal is to eliminate a thru hull and the attending plumbing and simplify with fewer components.
The requirements will be large enclosure, lots of forced air, lots of noise and heat. The air ducting path may abut accommodations = noise + heat. You will also need to find a path for dry exhaust and room for a good muffler and the attending lagging. You will have non standard unit that may be difficult to find service for if you cruise.

I believe the answer is: Not worth it

Air cooled isn't a good option for permanent mounting. It's a challenge to feed it enough air. Plus, air cooled units are LOUD.



As far as I know, the only company that currently makes new build gasoline fueled marine generators is Westerbeke.

The big question is what will it be used for?


Run a 50A battery charger several hours a day which the main engine or 8kW genset would be overkill...


Or power several electrical appliances plus a couple air conditioners where only a large diesel genset would be suitable.


Some just use a tiny 1000W Honda for the 50A charger demand....At $600 versus $8000+ .... and some stringent safety precautions the argument is pretty strong. Maybe not for some on either side of the safety question but for quite a few....it becomes the choice.


With something that small and quiet, with additional soundproofing, permanent mounting not required.

mvweebles said:

Dry stack is still water cooled, but a keel cooler instead of wet exhaust. Notably, Nordhavn uses wet exhaust on their dry-stack boats.

Click to expand...

Thanks! ndeed! I fired that email off with too few brain cells firing off a little too late at night! Sorry!

But, yep, keel coolers have been well discussed in the threads, too! And, unlikely to be worth it here, I'd guess.

-Greg

WOW - TY for many insightful immediate responses.

Let me clarify what I have and why I'm asking if there may be an air cooled genset designed for "marine" placement into the same enclosed engine compartment as our current gasoline, 7.A, 7.5 kW 1977 Kohler. See photo.

1. Just seems that air cooled, gasoline gensets are so easy damn to deal with and efficient too. I have had several over the years for my masonry, concrete and tile construction company. Also have one that runs our house when power gets shut off [which happens a few times a year to thwart fires in our wooded Nor Cal area.

2. Reliability - If I decide to rebuild or put in a new genset

3. Cost - In general

So... not that it too much matters about cost [somewhat though] - but - ongoing reliability, weight reduction and installation ease are also predominant factors.

I just wondered about possibility for air cooled genset. May simply take our boat 100 +/- miles to a Kohler specialist business and say - Do what you must to make current Kohler genset ready for another decade of use.

Stay safe! Stay healthy!!

Air cooled gas generators are not efficient at all. They're actually horrid for efficiency. I did an analysis on this over on Cruisersforum at one point. Basically, the air cooled units are likely less efficient than your old Kohler.



See my full analysis here: https://www.cruisersforum.com/forum...dditional-fuel-tank-230494-2.html#post3079298

rslifkin said:

Air cooled gas generators are not efficient at all. They're actually horrid for efficiency. I did an analysis on this over on Cruisersforum at one point. Basically, the air cooled units are likely less efficient than your old Kohler.



See my full analysis here: https://www.cruisersforum.com/forum...dditional-fuel-tank-230494-2.html#post3079298

Click to expand...

Thanks rs... Seems your analysis in link above is correct.

I'm not too fixed on fuel burn efficiency per kW. In that, we use our Tolly boat only as a pleasure swim/relax spot in our lives for some 10 to 15 weekends [and week long during national holidays] at anchor per year. I doubt our genset runs more than 100 hrs a year = 100 gallons gas = $400 +/- per year.

What I do want is a reliable genset that needs little to no attending, general maintenance of course.

Air cooled industrial small generators exist, or they existed and they worked very well. The advantages were no cooling system to malfunction.

One example given was the Lister engine.

Another example that folks do not realize was the Onan J series engine. Mariners know this engine as the MDJ series still in use by many boaters.

Take away the "M" and you have the DJ engine which was the same engine with fins on the head, a shroud and a fan to move the air.

These were extremely durable generators and were used by the military for a couple of decades. They were rated at 7 KW for the 2 cylinder model and 15KW for the four cylinder one. The military downrated them at 5 and 10KW respectivly.

The Onan J series engines were discontinued with the first round of emissions standards I think in the early 1980's

These were LOUD engines, with much of the noise being generated by the intake system.

I have enclosed the J series engine in a small "hut" or generator shed very successfully many times and my personal one ran for many years as my home backup generator. The hut was ventilated by two 12" exhaust fans, one forcing air into the hut and one exhausting that air.

It's funny but rebuilding those little engines for the prime power market in Alaska was what got me started in the backup power business many years ago. We have since then switched away from generation as a specialty, to supporting switchgear, but I will always fondly remember those noisy, durable engines.

I know gasoline engines have a reputation for not lasting as long as diesel, etc. But, I am still curious what type of reliability problem you are having?

My old Kohler (Diesel) was clearly of the same era, and hadn't been used for at least 5 years and maybe 10 years when I bought the boat. I primed it and adjusted the governor and a linkage rod to get the engine going, and it ran like a charm. I then replaced a resistor in the controller so it would stay going (it was part of a safety circuit). Then I cleaned out the cooling system and changed all of the fluids and filters and raw water impeller so I wouldn't make a mess of it with old stuff. Then I replaced a couple of other internal controller parts to fix the charging circuit (even though I never used it). And, I replaced the lifter pump, which a prior owner had supplemented with an electric pump. Eventually I tuned the governor and field resistor so the voltages and frequency were right across load levels. And, I then replaced the raw water and closed-loop cooling pumps (closed loop broke a shaft). I think I had the injectors rebuilt as part of a tune up, but don't remember. I never did the pump. Somewhere in there I also replaced the header cap and had the part where the water injection was welded into the exhaust pipe rewelded and wrapped the exhaust.

I had tried to get a Kohler dealer to work on it. But, basically they wouldn't. They'd all have been glad to give it a tune up or change fluids and filters or to swap a cooler or whatever. But, once there was a controller problem, they didn't want any part of it. Some said no. Some said that they were unlikely to be able to fix it, but would come out for $125/hr from the time they left their shop an hour away until they got back. And, one independent generator repair person looked at it, said nothing major was wrong, just something small in the controller. He was going to come back to fix it, but instead sent me the schematic via an SMS message and wished me luck. Mechanics would work on the engine, but not the generator back end.

...it took me hours and hours to learn how the generator works (I was new to boating, compounding my confusions). The folks in the legacy Kohler subforum at SmokStak (another forum specializing in such generators) were great.

Realistically, I went from a years-forgotten brick to a truly reliable generator for less than $1,000.00, most of that for the closed loop cooling pump.

One December I was at a mooring with a non-boating friend who loved creature comforts. That generator put out most of its capacity for days and its full capacity for an hour or so every evening when cooking.

For as old as it was, after I got the bugs worked out and built up some confidence with it a little at a time, I had no worries about it.

So, I guess I just want to encourage you to make sure you need a new generator before buying one. Personally, I've made errors both ways: Investing tons in things that needed replaced, and replacing things that should just have been repaired, calibrated, or used. One thing I've learned is that age, by itself, isn't a good prognosticator.

gkesden said:

I know gasoline engines have a reputation for not lasting as long as diesel, etc. But, I am still curious what type of reliability problem you are having?

My old Kohler (Diesel) was clearly of the same era, and hadn't been used for at least 5 years and maybe 10 years when I bought the boat. I primed it and adjusted the governor and a linkage rod to get the engine going, and it ran like a charm. I then replaced a resistor in the controller so it would stay going (it was part of a safety circuit). Then I cleaned out the cooling system and changed all of the fluids and filters and raw water impeller so I wouldn't make a mess of it with old stuff. Then I replaced a couple of other internal controller parts to fix the charging circuit (even though I never used it). And, I replaced the lifter pump, which a prior owner had supplemented with an electric pump. Eventually I tuned the governor and field resistor so the voltages and frequency were right across load levels. And, I then replaced the raw water and closed-loop cooling pumps (closed loop broke a shaft). I think I had the injectors rebuilt as part of a tune up, but don't remember. I never did the pump. Somewhere in there I also replaced the header cap and had the part where the water injection was welded into the exhaust pipe rewelded and wrapped the exhaust.

I had tried to get a Kohler dealer to work on it. But, basically they wouldn't. They'd all have been glad to give it a tune up or change fluids and filters or to swap a cooler or whatever. But, once there was a controller problem, they didn't want any part of it. Some said no. Some said that they were unlikely to be able to fix it, but would come out for $125/hr from the time they left their shop an hour away until they got back. And, one independent generator repair person looked at it, said nothing major was wrong, just something small in the controller. He was going to come back to fix it, but instead sent me the schematic via an SMS message and wished me luck. Mechanics would work on the engine, but not the generator back end.

...it took me hours and hours to learn how the generator works (I was new to boating, compounding my confusions). The folks in the legacy Kohler subforum at SmokStak (another forum specializing in such generators) were great.

Realistically, I went from a years-forgotten brick to a truly reliable generator for less than $1,000.00, most of that for the closed loop cooling pump.

One December I was at a mooring with a non-boating friend who loved creature comforts. That generator put out most of its capacity for days and its full capacity for an hour or so every evening when cooking.

For as old as it was, after I got the bugs worked out and built up some confidence with it a little at a time, I had no worries about it.

So, I guess I just want to encourage you to make sure you need a new generator before buying one. Personally, I've made errors both ways: Investing tons in things that needed replaced, and replacing things that should just have been repaired, calibrated, or used. One thing I've learned is that age, by itself, isn't a good prognosticator.

Click to expand...

Correct pk:"... age, by itself, isn't a prognosticator." However, aged materials and aged [often used] unit functions can lead to ongoing, different types of breakdowns. Especially a gen set having been in saltwater for 32 years, i.e. 75% of its life; freshwater since.

Our 1977 [44 yr. old] 7.A, 7.5 kW gasoline Kohler has no accounting of total hours [we calc we've put on 1,000 +/-]. Nor do I know if any major rebuild ever happened. We've had our Tolly since 2008 and I don't feel the genset was previously [fully or even partially] refurbished/rebuilt. If it had been used similar to our 100 hrs. per year it would have some 4,400 hrs on it. And, it may have considerably more... maybe less too??!!

Therefore; cooling system, exhaust system and general safety [auto switch off] controls now needing replacement/repair costs may seem relatively fruitless if some other portion too soon thereafter stops working [breaks down]. It's not exclusively the cost that I take into account... but, also and importantly the time consuming efforts required to either fix or replace. If I fix this genset now I'd want at least another decade of untroubled use. That would make her 54 years old.

I plan to call Kohler specialist in this area to discuss alternatives.

Realistically, if the generator runs well as-is and the engine isn't showing excessive oil consumption, I'd just do the following: compression test the engine to determine health. Replace exhaust elbow, refresh ignition system components, check generator brushes, etc. Assess condition of exhaust and cooling systems to determine what shape things are in. If everything looks healthy and it's running well, I wouldn't worry about replacement until a major or expensive component shows a problem or the engine shows signs of wearing out.

FWIW, my 1986 Onan is doing just fine, although it's only got 1414 hours on the meter (and I put a whopping 32 hours on it this past season). As far as cooling systems go, one of my engines and the generator still have their original heat exchangers. The other engine got a new heat exchanger this past year due to an external leak that wasn't worth fixing on a 35 year old piece.

I have worked on 3 boats with air cooled enclosed gen sets that worked reasonably well. All were installed in large work boat engine rooms. All had large fans in addition to the radiator fan. All 3 engine rooms had huge volume forced air flow. All 3 installations would overheat if worked too hard or the boat was running in hot weather. Based on that observation I think an enclosed air cooled gen in your Tolly's engine room would be a disappointment being prone to overheating. There are folks here that will run portable gasoline gen sets on the outside decks. To do so safely beware of the CO risk management as well as neutral / grounding.

Air cooled engines create much more interior heat than water cooled engines. It's very difficult to remove the extra heat.
Many years ago I ran a large tug for a cheap owner. He got a "deal" on a radiator cooled generator. Even though the engineroom had large, 36" diameter, axial blowers, moving air in and out, it raised the temperature about 20°F (more on hot days). The higher temps made the whole tug uncomfortable and caused the main engine to loose efficiency and use about 7% more fuel. After a couple long tows, the owner had a yard convert the generator to heat exchanger cooled. The generator eventually cost more that if he'd bought a proper one in the first place. Just sayin'.

Radiator cooled generators are not air cooled, they are water cooled with a radiator to dissipate heat.

Air cooled has no water at all, like a larger portable generator. I have a 10Kw unit as standby for hurricane season that's air cooled for example, just like a Honda 2000 only bigger

Keysdisease said:

Radiator cooled generators are not air cooled, they are water cooled with a radiator to dissipate heat.

Air cooled has no water at all, like a larger portable generator. I have a 10Kw unit as standby for hurricane season that's air cooled for example, just like a Honda 2000 only bigger

Click to expand...

That is true - except: A water filled radiator motor in enclosed area emits all the engine heat it collects into general proximity air. Where as a heat transfer system of a marine water cooling system transfers most of an engine's heat into the boat's surrounding waters.

And it would have to be ignition protected. So it would not be able to be a home grown genset since it would not be ignition protected and not be certified so your insurance company would have a huge problem with it.

Comodave said:

And it would have to be ignition protected. So it would not be able to be a home grown genset since it would not be ignition protected and not be certified so your insurance company would have a huge problem with it.

Click to expand...

So would I - LOL!!

However... if a marine design became desired... and a marine air cooled genset were to be developed... it could be made with ignition protections.

Yes, if there was a demand for it some company would have developed it with ignition protection. But since there isn’t a demand there aren’t any out there.

There is a clear division in the context of your question between water and air cooled engines. A water cooled engine has liquid running through the block to cool it, and that water transfers heat through a heat exchanger or a radiator, a raw water cooled engine just draws new water and discharges hot overboard.
Air cooled engines have no water in the block to dissipate heat. They are typically cooled by heat sink fins around the block which dissipate heat into the surrounding air.
Using your exception almost all cars are air cooled, except Corvairs and Volkswagen bugs, those (and others) really are air cooled.

Given your question and the premise that air cooled would be simpler because it has no active cooling system, radiator cooled systems have water pumps, plumbing, fans and a radiator. Freshwater cooled engines have a heat exchanger and attending plumbing instead of a radiator. I believe actually simpler and for sure smaller

Art said:

That is true - except: A water filled radiator motor in enclosed area emits all the engine heat it collects into general proximity air. Where as a heat transfer system of a marine water cooling system transfers most of an engine's heat into the boat's surrounding waters.

Click to expand...

Just to be clear, an engine with a radiator is liquid cooled. If I remember correctly, air-cooled engines are not legal below deck, at least in N America.

Fischer panda

Lostsailor13 said:

Fischer panda

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Junk . . . Oh, wait, I thought this was word association . . . . Well, from my experience, it still stands . . .