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Old 14-04-2016, 06:26   #1
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Attaching a 5KW generator to the main 45 HP boat engine

Is it possible and practical toc power a good size generator using the main boat engine? What would be the reasons not to attempt it?
The engine could be equipped with a clutch system similar to the AC system on a car and be turned on or off with an automated switch.
The RPM of the engine for power generation will be set based on the pulley system ratios but kept around 2000 rpm for efficient operation.
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Old 14-04-2016, 06:32   #2
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Re: Attaching a 5KW generator to the main 45 HP boat engine

It can and has been done, but there are reason not to as you would suspect.
If I were to try it, I think I may look for a transmission with a PTO, but one of the reasons not to, is hours on your main engine, and your running a much larger engine than required, burning more fuel, may not have room to mount all the equipment, belt driving a 5KW gen would be difficult to say the least, side loads on crank may be excessive and you'll likely need a governor set up that will hold engine RPM as loads change.

Ends up less money and less hassle and more efficient and less wear on main engine to install a stand alone generator, and they are usually much quieter as well.
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Old 14-04-2016, 06:49   #3
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Re: Attaching a 5KW generator to the main 45 HP boat engine

Of course you could do that.

It's just a big, expensive project is all.
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Old 14-04-2016, 07:00   #4
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Re: Attaching a 5KW generator to the main 45 HP boat engine

As A64 said, it can be done but by the time you address the issues, you have a more expensive, less efficient generator.
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Old 14-04-2016, 07:12   #5
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Re: Attaching a 5KW generator to the main 45 HP boat engine

Would this be a DC generator? Then you would have to invert so some inefficiency there as well. 10%??? or more loss. So your 4500w would get you how many amps at voltage requirements. And that is a big inverter too.

Better off with a deck mounted Honda. No work required. Just plug in.
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Old 14-04-2016, 07:14   #6
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Re: Attaching a 5KW generator to the main 45 HP boat engine

I will take a contrary position and say that it absolutely can be done, and economically.

The key is to make DC power, and not AC power. DC power does not require synchronizing the engine speed, and can be easily inverted to make AC power as required by AC consumers.

There are different solutions, the cheapest of which is to use a single school bus alternator with appropriate double belt or serpentine pulleys and a proper bracket. I get 2.5kW out of mine (Leece Neville 24v, 110 amp).

That's generally enough power for almost anything you might need to do -- I also have a heavy-duty 6.5 kW AC generator, but I could live off the alternator if I needed to.

However, it does not load up the main engine enough that you would really want to be running the engine very much just to turn the alternator. Depending on the size of the main, of course, but mine is 100hp.

So two of those, with a jackshaft, would be better, from that point of view, but of course engineering the jackshaft and finding space for it makes this is far more complex and expensive project than just a single one. But still much simpler than any kind of AC power from the main engine.

Or there are specialized heavy duty alternators made for military vehicles, which go up to many kilowatts. These are much more expensive than school bus alternators, but maybe worth it -- these are made for heavy duty bulk power production.

I could google up a few examples, but you can do that yourself.


I think for many boats it makes lots of sense not to have that second diesel engine. If you can engineer a system which puts a decent load on the main engine, then this could have a number of advantages.


My next boat will probably not have a normal generator like I have now, but will have a second much smaller propulsion engine driving dual school bus alternators off a jackshaft. The great advantage of this is that school bus alternators are dead simple devices which can be repaired in any third world auto electric shop. THere's also redundancy in using two of them. The goal is to make a very simple, robust system which has little to go wrong, and can be easily repaired in the field if something does.
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Old 14-04-2016, 08:01   #7
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Re: Attaching a 5KW generator to the main 45 HP boat engine

OP, commercial fish tugs and work boats frequently use shaft generators off their main engines.

It's not exactly the same as what you are asking, but its the same general principal. Of course fish tugs run their engines more than some sailboats because they need to run their PTO's for their net haulers and either back down on to their nets (trawlers) or motor to their next buoy (Gill netters) or just transit or trawl continuously.

Fishermen wouldn't do it if it wasn't economical. If you're a guy who motors a lot, I think it makes sense.

As a side note, you can run very economical bus style heaters off your engine at the same time.

Your theory makes sense for some boaters but not all.

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Old 14-04-2016, 08:32   #8
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Re: Attaching a 5KW generator to the main 45 HP boat engine

I put a 2.5 kW dc generator on each of my twin Diesels on my previous cat. Worked OK, but was hard on belts. Both engines died at 5500 hours (+-). I asked Yanmar and they said the engines were "overpropped" as a result of the additional generator load.

Be sure, if you add load, that your engine is still capable of reaching rated RPM at wide open throttle - if not, you are adding fuel as the governor tries to reach rated rpm - and the unburned fuel dilutes the oil, causing possibly premature engine failure.

Still seemed OK with me - two rebuilds at 5500 hours were cheaper than a genset and its related weight and maintenance.
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Old 14-04-2016, 09:00   #9
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Re: Attaching a 5KW generator to the main 45 HP boat engine

Reasons for not adding a large generator to your engine:
1. The main engine should be standalone from everything else. It is your main source of propulsion and you will rely on it. Keep it simple and independant.
2. Running a diesel lightly loaded will ruin the bores and she will smoke,
3. Use solar power. I have cruised for many years without a generator at all. Solar panels really are the best way to go and the power is free! Your main load is refrigeration. Use a Waeco compressor system for minumum power requirement and fit a computer cooliing fan to blow air onto the condensor at the back of the fridge or freezer.
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Old 14-04-2016, 09:36   #10
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Re: Attaching a 5KW generator to the main 45 HP boat engine

Quote:
Originally Posted by a64pilot View Post
It can and has been done, but there are reason not to as you would suspect.
If I were to try it, I think I may look for a transmission with a PTO, but one of the reasons not to, is hours on your main engine, and your running a much larger engine than required, burning more fuel, may not have room to mount all the equipment, belt driving a 5KW gen would be difficult to say the least, side loads on crank may be excessive and you'll likely need a governor set up that will hold engine RPM as loads change.

Ends up less money and less hassle and more efficient and less wear on main engine to install a stand alone generator, and they are usually much quieter as well.
What about alternator on flywill?
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Old 14-04-2016, 10:13   #11
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Re: Attaching a 5KW generator to the main 45 HP boat engine

Anything is possible. Practical is another story.
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Old 14-04-2016, 10:40   #12
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Re: Attaching a 5KW generator to the main 45 HP boat engine

Quote:
Originally Posted by mikecambrai View Post
Reasons for not adding a large generator to your engine:
1. The main engine should be standalone from everything else. It is your main source of propulsion and you will rely on it. Keep it simple and independant.
2. Running a diesel lightly loaded will ruin the bores and she will smoke,
3. Use solar power. I have cruised for many years without a generator at all. Solar panels really are the best way to go and the power is free! Your main load is refrigeration. Use a Waeco compressor system for minumum power requirement and fit a computer cooliing fan to blow air onto the condensor at the back of the fridge or freezer.
Solar is wonderful and if you have room for it, that is for enough to supply your needs, it's definitely the best source of power you can have. Had it on the last boat and loved it. Note that solar works particularly well with lead acid batteries.


Running a diesel too lightly loaded can be harmful, but what is too lightly? I think 3 or 4 kW for a 45 horsepower engine is a decent load.


Concerning independence of the main engine, I don't get this. Why? Adding a larger alternator will not compromise the main engine.
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Old 14-04-2016, 10:56   #13
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Re: Attaching a 5KW generator to the main 45 HP boat engine

In my experience, 4kw would be too light a load and you would at least have to load up the engine every half hour or so just to clear it. Light loading glazes the bores and is expensive to cure.
Anything that you do to an engine to make it non standard can affect reliability particularly if you don't know what the effect that your modification can give. When the chips are down and the weather is bad I like to be able to rely on an engine that is not going to fail because of some modification that I may have done. So I just don't do it.
Even connecting a calorifier to the cooling water is a modification and would need stop valves at the inlet and outlet such that you can turn off the modification. Adding a larger alternator to the front pulley can stress the crankshaft. You really don't want any chance that the engine is going to fail when you need it the most, so don't modify it.
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Old 14-04-2016, 11:08   #14
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Re: Attaching a 5KW generator to the main 45 HP boat engine

Quote:
Originally Posted by mikecambrai View Post
In my experience, 4kw would be too light a load and you would at least have to load up the engine every half hour or so just to clear it. Light loading glazes the bores and is expensive to cure.
Anything that you do to an engine to make it non standard can affect reliability particularly if you don't know what the effect that your modification can give. When the chips are down and the weather is bad I like to be able to rely on an engine that is not going to fail because of some modification that I may have done. So I just don't do it.
Even connecting a calorifier to the cooling water is a modification and would need stop valves at the inlet and outlet such that you can turn off the modification. Adding a larger alternator to the front pulley can stress the crankshaft. You really don't want any chance that the engine is going to fail when you need it the most, so don't modify it.
Generating 4kW of power takes about 8hp of mechanical power, so 18% of rated maximum -- you sure that's harmful? I don't think I'm using more than that at economical cruise with my engine. In fact judging by fuel consumption I'm only using about 12-13 hp or 12% - 13%. I would think a 4kW generator would be an ok load even for my 100hp Yahmar.

Of course following Yanmar's instructions you have to open it up periodically, but I do that economical cruising too.
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Old 14-04-2016, 11:43   #15
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Re: Attaching a 5KW generator to the main 45 HP boat engine

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Anything is possible. Practical is another story.
PS, don't listen to the long winded BS. It would be a mechanical night mare. I doubt a junk yard AC clutch would do it, if that is what you are thinking along with the gen. probably needing a pillow block to support the shaft on the outside end. A nice idea if you are a mechinest JMHO
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