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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 01-04-2008
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Replace Atomic 4 with Electric Motor?

I am completing the refit of a 1974 Seafarer 34’ ketch that I acquired from a gentleman who couldn’t complete it. I wanted to install a generator of sufficient size to provide the comforts of air conditioning and a refer. I know generators can be had that are not real heavy and would work for my needs but I have a 4 cylinder diesel 20Kw Onan marine generator I bought for another project I’d like to use. It occurred to me I could pull the Atomic 4 and replace it with the Onan and an electric motor.

I haven’t done a lot of reading on the electric motors (yet). What are the pros and cons with the electric motors? I’m guessing I won’t be able to pick up parts at the local marina like I can for the Atomic 4, but other than that what should I look for?
Since the motors are electric, is there just a switch to reverse polarity so I won’t need a transmission (more weight savings)?

Full of questions (and other stuff), not many answers, so – bring it on! 8~)
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Old 01-04-2008
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From what I've read about using electric motors, I would say you'd be better off keeping the A4. At least from a cost basis.
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PB - please expound. Are you referring to maintenance; lifetime $/hr; original cost; etc?
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Old 01-04-2008
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Installation, upkeep, reliability. All the electric motors I've read about, employ a large battery bank as part of the install, charging the batteries, rather than running the motor. You're pushing quite a bit of boat there, and at a guess (I'm not an electrical expert), the size motor necessary could be prohibative in regards to space and generator output.
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Good points. I've been doing a little reading this morning and unless I have only found the sites that are full of BS, it appears 7-9 Kw is sufficient for powering electric motors large enough (25 - 30 h.p.) for my boat. With a 20Kw generator I would think I'd have enough current run the engine off the genny and charge the battery bank as well while running.
I have the space available for the batteries, and the area currently taken up by the A-4 would easily fit the diesel/genny.

Now please keep in mind - I broke my leg in 2 places a week ago and the pain meds result in me having all of these "great ideas". Probably not a good thing since my great ideas from a clear head don't usually pan out that well...
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Wannafish,
Stick with the A-4. They're great engines, and inexpensive to fix/overhaul. Take the money you'll be saving and stick it elsewhere in the boat. I have one, and it always gets me home. I'm always having to do this and that to it, but in many important respects it's better than a deisel. I can't imagine an electric motor, with its massive battery bank, is going to be lighter than your A-4.
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The main point I would make, from simply a common sense standpoint, is that if it was a workable idea, someone would be doing it by now. By having to run the genset to power the motor, you basically lose the positives of using electric, since you're still running a internal combustion motor anyway.
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Full, is the spirit, that thinks not, of falling.
True, is the soul, that hesitates not, to give.
Alive, is the one, that believes, in love.
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Three things...

First, electric motors generally don't mix well with wet bilges and their lifespan will be far shorter than you'd think.

Second, as PBZeer has pointed out, if you're running the motor directly off the genset, you lose most of the advantages of having an electric motor. Also, the idea of running it directly from a genset is not all that bright, since gensets loads are generally only for resistive loads—they're generally half as efficient for inductive loads. Also, most motors suitable for this type of work are probably 36 VDC or 48VDC and few gensets put out that much DC voltage.

Third, you'll still have all the problems of running a diesel with the added complexity of the electric motor setup. Your fuel efficiency will suffer seriously, since you now have the electric motor losses as well as the genset losses.
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There is a company that advertises in most of the sailing magazines that specializes in electric drive systems. Re-E-Power. They claim that you can use it as a regenerative system while under sail, and a 4 year warranty.

As for the battery capacity of your boat, I don't see this as an issue. You said that you have a big honkin' generator. I am guessing that you want to use this as the power source, not the batteries. You would start the generator, as you would start the auxilliary on a regular boat, then use the throttle and transmission as you would normally. I beleive that Lepoard Catamarans use this same architecture with their electric versions.

I believe that the real benefit of such a system is that you are not as restricted about where the generator is placed on the boat, as you would be with a conventional (mechanical) drive train. If you wanted to put it in the sail locker to free up additional cabin space, you could. (I'm not saying that this is a good idea...)

That said, I agree with 'Hog and 'Dog that you would probably be better off spending those shrinking dollars elsewhere on your boat.

I suspect that the weakest link in the system is the drive control. Controlling all that current is going to require some heavy duty switches. Putting them in a high moistrure / humidity environment is askin' for corrosion problems. IIRC Lepoard has had some issues with their drive control software which is probably related to this humidity issue. (I think that there was a CW article on this last year).

Hope this helps!

Ed
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Ed-

The Leopard Catamarans that are electric drive, use a battery-based system with a huge honking battery bank. They also have a diesel genset to charge the battery bank, but the motors are run from the batteries.
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