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Old 06-01-2016, 05:33   #1
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Ideal Generator?

I'm still collecting ideas and thoughts for my next boat, if there ever is one, which will definitely be custom built. I started a thread about it last year which I can't find.

I was reading Noelex's classified ad for his old boat, and among many other excellent features, really liked his generator. It's a standard boat propulsion engine -- so already marinized with standard parts -- a huge plus for serviceability and parts availability -- driving a standard heavy duty alternator -- ditto. This is similar to some home-made DC generators we've seen on here, except that instead of a home-made marinization of an undersized Kubota, this just uses a standard propulsion engine from a much smaller boat.

For a long-distance high latitude adventure cruising boat, I think this is just the ticket -- the ultimate in robustness, serviceability, and simplicity.

I am not a fanboy of DC generators because I don't see any overwhelming advantage in efficiency. Now that we have modern charger/inverters which make a seamless conversion between DC and AC and back, I don't think we really care whether power comes to us in DC or AC form. I like heavy duty low speed AC generators and have had excellent service from my Kohler EFOZ6.5 and would not trade it for a homemade DC generator with a home-marinized Kubota, but something like Noelex's generator is something very different.

I think on my next boat I'll have something like that. I would use a Beta or Nanni, the smallest 3-cylinder propulsion engine they make. I would have a flywheel and jackshaft in place of the gearbox running two large frame Leece-Neville 36 volt or 48 volt alternators through short toothed belts. That will give a capacity of up to 6 or 7kW with both running, but by varying the engine speed and using one rather than both alternators, the output can be regulated.

I would have a third identical 36 or 48 volt alternator on the main engine. This gives great flexibility and redundancy in power generation, and one spares kit will cover all three alternators.

This power will charge a 36v or 48v battery bank, maybe LiFePo, which can absorb high charge rates, using this generator to its best advantage and allowing for short generator runs.

Having this kind of power on board eliminates the question of how to power the windlass, bow thruster, and furling gear.

The DC bank will produce AC power through ganged charger-inverters, maybe three like the Victron Multiplus I have now. This is not an ideally reliable unit, but in a gang of three the built-in redundancy will compensate. Like that there will be about 7.5kW of available AC power.

DC consumers powered through 24v or 12v droppers. Probably there will be one large 24v dropper powering a separate 24v bus.


To make the generator perfectly serviceable, I guess is should live above the main engine and under the cockpit sole. If this is bolted in place and easily removeable, or with a large opening hatch, then access should be ideal.

Everything needed to make the generator run, including its start battery, should be located right there in the same place and should be separated as much as possible from other systems.

Such a generator makes it easy to take off mechanical power for other purposes, but I think there's hardly any point to a mechanically driven watermaker pump or bilge pump, since you have nearly unlimited electrical power for this. Maybe a large mechanical bilge pump would make sense just for the case of some disaster which has knocked out power, but you can still start the generator since its start battery is separate and well above the waterline.
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Old 06-01-2016, 05:55   #2
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Re: Ideal Generator?

I think your idea of using a small propulsion plant is spectacular DH!
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Old 06-01-2016, 06:08   #3
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Re: Ideal Generator?

Why not just use the main engine for it. One less engine to service. Add a big engine driven watermaker and you can really take advantage of it. With Lithium batts, an hour or two every other day or so will keep batteries and water tanks topped up. I think the load of a big alternator is enough to keep the cylinders from varnishing up. That seems to only happen with no load and there is not a lot of evidence that its a real problem anyway.
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Old 06-01-2016, 06:12   #4
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Re: Ideal Generator?

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I think your idea of using a small propulsion plant is spectacular DH!
Yes, except not my idea!

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Old 06-01-2016, 06:13   #5
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Re: Ideal Generator?

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Why not just use the main engine for it. One less engine to service. Add a big engine driven watermaker and you can really take advantage of it. With Lithium batts, an hour or two every other day or so will keep batteries and water tanks topped up. I think the load of a big alternator is enough to keep the cylinders from varnishing up. That seems to only happen with no load and there is not a lot of evidence that its a real problem anyway.
A valid approach absolutely. I'm also considering this.

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Old 06-01-2016, 06:18   #6
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Re: Ideal Generator?

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A valid approach absolutely. I'm also considering this.
Well, you're on the right track. Now all you have to do is make it a catamaran.
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Old 06-01-2016, 06:18   #7
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Re: Ideal Generator?

Mono hull?
Get real slick, have two "real" engines driving hydraulic pumps, main propulsion and everything else is hydraulically driven, add as many users as you want and have nearly complete redundancy. The bigger the boat, the more sense it makes, but even I have seen hydraulic furlers and bow thrusters

You pay the bill though, cause I can't
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Old 06-01-2016, 08:07   #8
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Re: Ideal Generator?

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Well, you're on the right track. Now all you have to do is make it a catamaran.
Well, the two top boats on my short list, among regular production boats, were the Hallberg Rassy 64 and the Chris White Atlantic 57 cat. The Atlantic cat really pushes a lot of my buttons and suits my needs very well in many ways, and for half the cost of building myself, probably. But neither was quite "it" in all respects, which is why I decided to build despite the cost.

Cats have many inherent advantages, and one very great advantage is that they are superb motorboats, and have redundant power plants. You certainly don't need a third diesel engine on a big cat -- just put big school bus alternators on both the main engines. Problem solved.
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Old 06-01-2016, 08:09   #9
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Re: Ideal Generator?

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Mono hull?
Get real slick, have two "real" engines driving hydraulic pumps, main propulsion and everything else is hydraulically driven, add as many users as you want and have nearly complete redundancy. The bigger the boat, the more sense it makes, but even I have seen hydraulic furlers and bow thrusters

You pay the bill though, cause I can't
Indirect drive has a lot of advantages, although I would probably go electric rather than hydraulic (in fact I've never seen hydraulic drive on a yacht; does it exist?).

But it grossly violates the "KISS" principle, which is why I elected to go with the rugged and simple and serviceable choice of direct shaft drive, with a Hundested propeller.
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Old 06-01-2016, 08:18   #10
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Re: Ideal Generator?

Dockhead you've waxed lyrical on other threads about your coming boat. So when are you going to get real and built the bloody thing?

I'll happily volunteer my services to help you think up dodads and thingamagigs that are absolutely essential on such a yacht and since you are a really nice guy....................

why I'll volunteer to sail sea trials and deliver it for you

Am I not just a swell guy?

And I'll also let you write the check for this - it is out of my pay grade.
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Old 06-01-2016, 08:20   #11
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Re: Ideal Generator?

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Dockhead you've waxed lyrical on other threads about your coming boat. So when are you going to get real and built the bloody thing?

I'll happily volunteer my services to help you think up dodads and thingamagigs that are absolutely essential on such a yacht and since you are a really nice guy....................

why I'll volunteer to sail sea trials and deliver it for you

Am I not just a swell guy?

And I'll also let you write the check for this - it is out of my pay grade.
Hah, I have to earn the money for it first. So far this project is a pipe dream, but there is a fair chance it could become reality in two years time, so now is the time to be thinking through the design brief.

You'll definitely be on the crew list, unless you are off in the South Pacific or somewhere

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Old 06-01-2016, 08:28   #12
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Re: Ideal Generator?

Another intriguing possibility is to place the smaller engine alongside the main engine, and give it its own shaft and prop. Then you get a wing engine besides just a generator. And you can use the smaller engine for extremely efficient slow motoring in flat calm weather.

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Old 06-01-2016, 08:52   #13
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Re: Ideal Generator?

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You'll definitely be on the crew list, unless you are off in the South Pacific or somewhere

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Old 06-01-2016, 08:53   #14
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Re: Ideal Generator?

I have never seen hydraulic drive on a yacht, but many ferries etc., but then how many Yachts have I seen, not many.
Hydraulic is about as KISS as it gets, very simple system and I'd want it for redundancy of two power plants, and the more customers you have, the more sense it makes, hydraulic thrusters and furlers I think are mainstream.
One of it's advantages is you can now put the engine(s) anywhere you want to, even get real slick and have a retractable drive, anything is possible if you have enough money.

Same for electric I guess, I'm just more comfortable with hydraulics in salt water.

I don't think you can replace an AC generator with alternators, not really. Forgetting conversion losses just to power a 30 amp boat, you need 300 amps of 12 VDC, half that for 24 of course.
I haven't yet seen an alternator make full, rated output, especially not continuously.
I suspect the real, continuous output of an average alternator is about half, maybe three quarters of its rated power at best.
With a huge battery bank, and massive charging capability, I guess you could replace a generator.
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Old 06-01-2016, 08:57   #15
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Re: Ideal Generator?

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Another intriguing possibility is to place the smaller engine alongside the main engine, and give it its own shaft and prop. Then you get a wing engine besides just a generator. And you can use the smaller engine for extremely efficient slow motoring in flat calm weather.

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Back to that hydraulic thing, run one engine for efficiency, both for speed, and since they are identical and redundant, spares ought to be easy and you could cannibalize one for the other if you had to.
Twin drives in the water is of course twice the drag. I don't know how much drag a sail drive is compared to the hull, but I bet it's not insignificant.
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