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Old 30-05-2024, 18:09   #1
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Main engines as a replacement for our generator?

We're a sailing catamaran with two Yanmar 4JH57's each with about 1100 hours. We have a Paguro (3600 rpm) 8.5KW generator with 600 hours since 2018.

We have Lithium batteries and get about 95% of our charging from solar. We would love to save the space and weight by getting rid of the generator but when we need it we usually really need it.

Currently, our main engines only charge the start batteries then a DC/DC charger charges the lithium at a total of 60 ah which isn't enough to make it worthwhile to use the engines to charge.

We're looking to replace our air conditioners with DC units making it where the only thing we need the generator for us charging the house bank.

What are the thoughts on installing something like the Zeus alternators and regulators and using the main engine as a replacement for our generators?

Is it worth it for the extra wear on the engines? Would the low load (if it is) on the engines cause issues if they are running in generation mode for a few hours at anchor?
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Old 30-05-2024, 19:35   #2
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Re: Main engines as a replacement for our generator?

Just saw the same question in another thread. Nevermind!
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Old 30-05-2024, 19:54   #3
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Re: Main engines as a replacement for our generator?

Just curious how you have 11000 hours on those diesels already as they only came out with that model 5-6 years ago? Do you really average 5+ engine hours per day?
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Old 31-05-2024, 03:27   #4
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Re: Main engines as a replacement for our generator?

In general, you can do this with properly regulated large frame alternator, but the genset is almost new and your mains are definitely not. You sure it's worth changing stuff? That's major surgery.
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Old 31-05-2024, 11:53   #5
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Re: Main engines as a replacement for our generator?

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Originally Posted by malbert73 View Post
Just curious how you have 11000 hours on those diesels already as they only came out with that model 5-6 years ago? Do you really average 5+ engine hours per day?
1100 hours. Sorry, can't edit the post.
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Old 31-05-2024, 19:08   #6
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Re: Main engines as a replacement for our generator?

We have the same dilemma as the OP, though we had removed the existing genset a few years ago when the refit cost was going to equal a new unit (a Mase IS4.0 with 2000 hours, basically falling apart) and our main engines have 4500 hours each. We have 2.6KW of solar. We have retained the cooling water and exhaust systems in the generator area.

Current plan is high output alternators directly charging the LFP batteries and having just two diesel engines to maintain. But maybe getting a new low RPM generator like Northern Lights would prevent our propulsion engines getting more worn and will provide more robust generating?

We will be heading from tropical and equatorial areas to predominantly cloudy mid and high latitudes in the next few years and solar will not be sufficiently reliable.
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Old 31-05-2024, 19:39   #7
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Re: Main engines as a replacement for our generator?

To me it's somewhat a question of how often you need to generate power at times when you wouldn't otherwise have a reason to run the mains. And also a question of how much power you need.
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Old 01-06-2024, 02:54   #8
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Re: Main engines as a replacement for our generator?

Quote:
Originally Posted by fxykty View Post
We have the same dilemma as the OP, though we had removed the existing genset a few years ago when the refit cost was going to equal a new unit (a Mase IS4.0 with 2000 hours, basically falling apart) and our main engines have 4500 hours each. We have 2.6KW of solar. We have retained the cooling water and exhaust systems in the generator area.

Current plan is high output alternators directly charging the LFP batteries and having just two diesel engines to maintain. But maybe getting a new low RPM generator like Northern Lights would prevent our propulsion engines getting more worn and will provide more robust generating?

We will be heading from tropical and equatorial areas to predominantly cloudy mid and high latitudes in the next few years and solar will not be sufficiently reliable.
Let us know how it works out. But 2.6kW is a lot of solar. You won't need AC in higher latitudes, and your solar output will be improved by lower temperatures. I bet you will be fine like that.

I don't have any solar on my monohull because of sailing performance concerns. If I had a cat, which doesn't heel, I would splash out on solar, and I am pretty sure a couple of heavy duty alternators would be all I need. Three diesel engines on a weight-sensitive cat seems a lot to me.

For me, the big question would be AC. If you think you will ever need to run AC for hours at a time off shore power, I wouldn't want to use a main engine for that.


Now I cruised in semi-tropical climes for more than a decade with a boat with AC but no generator. We ran the AC at docks and used wind scoops at anchor. Depending on your use case, that could be ok. With a large lithium battery bank you might get away using a very small AC unit in your sleeping cabin, off batteries.
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"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
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Old 01-06-2024, 06:42   #9
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Re: Main engines as a replacement for our generator?

I used a 3500 BTU AC for the V-berth area. It was a 120 vac Dometic unit that came with a 400 watt inverter. The house battery bank was three group 31 AGMs, about 300 amp hours. The main engine had a 100 amp alternator with a Balmar smart charger and would average 70 to 75 amps to the house bank. I had solar and wind chargers, but only averaged 5 to 8 amps from the units combined.

While cruising the Gulf of Mexico coast, I could get 5 to 6 hours of cooling before the house bank was down to half charge, 120 amp hours used. This was adequate for my needs. Three to four hours of motor sailing would recharge the house bank.
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