# Replace Atomic 4 with Electric Motor?



## Wannafish (Mar 25, 2004)

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.
<O</O
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)?
<O</O
Full of questions (and other stuff), not many answers, so - bring it on! 8~)


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## PBzeer (Nov 11, 2002)

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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## Wannafish (Mar 25, 2004)

PB - please expound. Are you referring to maintenance; lifetime $/hr; original cost; etc?


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## PBzeer (Nov 11, 2002)

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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## Wannafish (Mar 25, 2004)

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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## sailhog (Dec 11, 2006)

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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## PBzeer (Nov 11, 2002)

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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## sailingdog (Mar 19, 2006)

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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## eherlihy (Jan 2, 2007)

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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## sailingdog (Mar 19, 2006)

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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## eherlihy (Jan 2, 2007)

Thanks SD. IIRC the article was about the Lepoard 4300E, which is also used by the Moorings as their 4300.

But now I'm confused... From http://www.cruisingworld.com/boats-...catamaran-draws-the-vibes-in-miami-49968.html
"The Moorings 4300 relies on a diesel-powered DC generator, which drives the electric propulsion unit in a green box located "under an aft bunk that measures one foot by two feet by one foot," says Burton. "It's incredible."

According to the Moorings, what makes the system unique is that the propulsion system doesn't use extra batteries for energy storage; instead, it combines Glacier Bay's OSSA Powerlite propulsion unit with an OSSA Powerlite DC generator system, which also feeds the boat's other house systems."

I dropped my membership in CW, so I don't think that I can dig up the original article.


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## TSOJOURNER (Dec 16, 1999)

We have been using a Minnkota 55Lbs. thrust trolling motor for our 20' boat for two seasons now. It runs for ~3 hours at max thrust off of two type 24 batteries and the whole assembly (seems to) weigh about as much as the 8HP motor and a full gas tank. The OB is for sale, BTW 

In my research, I found that electric is not really measured in HP, but in pounds of thrust. A rough conversion is 1Lbs thrust to 1HP, but then the discussion gets very technical (to me) in terms of prop shape. Basically, my electric motor does not ever get us going fast- tops is about 4-5 knots VoG, but we can go that velocity in a 30 knot wind. Yeah, we probably should not have tried sailing that day!

I have been thinking about mounting the motor directly to the boat instead of off the transom motor bracket. Re-e-power is top of my list and I hope to run into them at a boat show soon. There is at least one other company that sells an 'electric engine' for boats. Re-e-power's design sits outside the hull, like my idea to mount the Minnkota (Minnkota also sells engine mount electric motors that look like they could be attached to the hull easily). The other option I saw on the web uses an electric motor inside the boat- a la replacing the Atomic.

I like the regenerative aspect of Re-e-power, but cannot find any data on it. Does anyone else use one or have information? I imagine it would work much like a towed generator, but how many amps/knot would be nice to see on their webpage.


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## sailingdog (Mar 19, 2006)

IIRC, the Lagoons use a regenerative system that allows them to use the prop to generate electricity under sail. There was an article about it here. A regenerative system by definition needs batteries or some other form of energy storage.


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## Wannafish (Mar 25, 2004)

Lots of valuable insight here, and all appreciated. My thoughts were if I'm going to have a generator anyway, why not have it large enough to drive the propulsion system too. Especially since I had heard of others (though definately not in the majority) doing something similiar.

Concerns about wet environments for electrical systems, and the need to change the AC oupout of the Genny over to DC hadn't even crossed my mind. That in itself is probably enough to eliminate my changeover. 
Even if I could overcome those issues, I have a feeling there are a dozen more that haven't been discussed yet that would in turn lead to a dozen more...

Thanks to all for the input. I haven't necessarily crossed it off my "must have" list - but is is moving further and further down it.

More comments are most welcome!


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## HoffaLives (Feb 19, 2007)

you should really consider doing more in-depth research. what you are proposing is really on the cutting edge of new boat technology, and as such there are a lot of questions and the cost is high. But from what I've researched, electric marine motors are much more reliable and quiet and efficient than the best internal combustion engine. hell, only one moving part! it's the batteries that makes the cost high and maintenance becomes more of an issue. but that's the big bugaboo with any battery-powered form of transport.

the genset to electric motor is actually quite old technology and has been used on many applications including freight trains for years. but while it has great advantages when moving hundreds of thousands of tons, it likely loses some in the micro scale you are talking about.


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## Quickstep192 (Jan 6, 2001)

The Hinckley 42 daysailer has an electric motor.


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## sailingdog (Mar 19, 2006)

Freight trains have less issues with weight and mass, and don't subject the electrical system to quite so much salt water or humidity. Also, the one major problem with them is getting a reliable throttle system... and one that isn't going to die under the conditions that a small sailboat would subject it to. Most small sailboats are fairly wet beasties... unlike a Lagoon 40'+ catamaran-they heel, they take water over the rail, they get water in the cockpit that sometimes ends up in the bilge... etc.



HoffaLives said:


> you should really consider doing more in-depth research. what you are proposing is really on the cutting edge of new boat technology, and as such there are a lot of questions and the cost is high. But from what I've researched, electric marine motors are much more reliable and quiet and efficient than the best internal combustion engine. hell, only one moving part! it's the batteries that makes the cost high and maintenance becomes more of an issue. but that's the big bugaboo with any battery-powered form of transport.
> 
> the genset to electric motor is actually quite old technology and has been used on many applications including freight trains for years. but while it has great advantages when moving hundreds of thousands of tons, it likely loses some in the micro scale you are talking about.


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## Captsomer (Dec 20, 2007)

I think the technology for the electric drive system is here and available today. The prices are still a bit high but…. Several companies have systems that have been working fine, and the electric car guys have been at it for a while with success. I think as the battery technology continues to advance, this idea will become more and more popular and the prices will become a bit more reasonable. 

Anyway, contact Electric Vehicles of America (Google them). They have built electric propulsion systems for boats before. They should be able the assist you. Also try elcoelectriclaunch.com, they build some very nice launches that are powered by electric. 

PS If an electric golf cart can withstand all the abuse that it sees and keep on going, I think we can put a similar system in a boat and expect it to run also. There are ways of keeping things reasonably dry and clean.


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## TSOJOURNER (Dec 16, 1999)

Hello,
New to this forum, but glad to see the discussion about electric propulsion. Re-e-power has electric motors, of various sizes, that mount to the bottom of your haul similiar to a saildrive that operate at either 36 or 48 volts which means you only need 3, 4, or 6 (12v or 6v) batteries wired in series. Their control systems are based on the tried and tested electric golf cart controllers and switches able to take serious abuse and available anywhere golf carts parts are sold. A real do-it-yourself system which I have installed on my 1976 Southcoast 22. I just did a test run of the new system 2000+ on Lake Erie on Jan. 6, 08 and video taped it. Check it out at youtube and search danielmendat. (Can't post links yet, I'm too new) My original motor was a 6hp Johnson 2 stroke and I can say after this last test that the E-pod is as powerful if not more and much more maneuverable. The video will explain why. I don't work for re-e-power, its just the solution that I've been looking for since I bought my trailer sailor. Nothing better than silently leaving the dock to set sail. No fumes, no stalling, no gear grinding, no fuel tank, and no greasy hands. Best thing I ever bought. 
Dan Mendat
1976 SC 22
"Silence"


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## jonlgauthier (Apr 27, 2000)

Wannafish,

I'm guessing you've been dissuaded from trying to go the _diesel-electric_ route (the correct term for what you were thinking of doing).

Overall, the concept is great, but you won't be able to do it very well - and cheaply - by using your existing Onan genset.

For one, electric propulsion motors (with the exception of the Re-E-Power) typically run at 240Vdc or higher. Your Onan produces 120/240Vac. And it probably isn't rated for propulsion duty. The engine may be, but the generator may not be able to put out near max current continually. And an AC induction motor for propulsion gets a bit complicated when it comes to speed control. You'd have to modify the genset output to DC.

I looked into it when we were repowering our Formosa 51 - and couldn't justify the cost - it would have been about double the installed cost of our Westerbeke 120-T4 and their BTD7.6 genset. Let the boatbuilders get some experience and the quantity up so that the price comes down - in the future I believe all 30-34 footers will be diesel-electric. They are more fuel-efficient, and the ability to have a prop with full torque at just a few RPM's give new meaning to low-speed handling.


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## engele (Nov 26, 2006)

*Electric*

From what I understand, you should be able to do electric in your boat fairly inexpensively. There are a lot more options out there today than there were a few years ago. I know here in my hometown there is a company that has just launched a prototype successfully and will be selling drop in repower engines shortly.

It really depends on what you want to do, but I have a hard time believing that you Atomic 4 is as good as an electric. The A4 is a simple, yet constantly breaking engine that is gas. I would look into it more, but I know there are successful electric drive systems out there.


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## mjrogers (Oct 31, 2007)

Sounds like a hybrid propulsion system to me. At one point I was looking for a plug in electric / plug in hybrid car. I found a lot of resource through:
Plug In America 
Nothing there about boats but could steer you toward resources and information.


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## steel (Sep 1, 2010)

Wannafish said:


> Lots of valuable insight here, and all appreciated. My thoughts were if I'm going to have a generator anyway, why not have it large enough to drive the propulsion system too. Especially since I had heard of others (though definately not in the majority) doing something similiar.
> 
> Concerns about wet environments for electrical systems, and the need to change the AC oupout of the Genny over to DC hadn't even crossed my mind. That in itself is probably enough to eliminate my changeover.
> Even if I could overcome those issues, I have a feeling there are a dozen more that haven't been discussed yet that would in turn lead to a dozen more...
> ...


I know this thread is two years old but I just came across it. As far as I can see it is a very good idea if you are someone who already owns a good generator, such as a diesel 1800 rpm 3-phase one.

Wannafish,
The first thing is I hope your generator is 3-phase. Big electric motors especially the cheap used ones found on eBay are 3-phase. 3-phase motors are smaller since they do not need the second coil and capacitor for starting.

You can get a big used motor in 1800 or 3600 RPM and hook it up to where the old engine used to be. Reversing the motor is done by reversing two of the 3 input wires with a switch.

Lowering the speed of the motor will be the hardest thing. You will have to lower the engine RPM on your generator, and you might have to modify the voltage regulator on the alternator. To run at half speed you run the generator at 900 RPM instead of 1800 RPM. Instead of 240V @ 60 cycles you'll have 30 cycles at hopefully around 140V (the optimal amount that the voltage should be lowered when the frequency is lowered is determined by the coil resistance over reactance in the motor). Hopefully the regulator in the generator won't regulate the voltage back up near 240V when you're running at half speed. Doing that will cause the motor to overheat, even though it will still be running at half speed.

You can lower the speed of your generator when it is under some load and measure the voltage with a volt meter. If the voltage lowers proportionally to the rpm then this is a piece of cake.

All of the other motors in your boat will slow down too. This won't hurt them though. Lights will get dim. Everything will slow down. The air conditioner won't be as cold.

Or you can get some kind of motor speed controller which runs an AC or DC or a fancy brushless DC motor. That'll be expensive.

I assume you're not interested in using batteries. But if you do go the DC route you could throw in a battery bank of maybe 4 batteries which would let you creep a long for a while in relaxing silence.


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## Waltthesalt (Sep 22, 2009)

I agree with all that's been said. If you do this you're adding a lot of risk and uncertainty to the project. This is sorta' cutting edge building you custom diesel/electric drive. Unless you're EE you may find getting everything matched up right could an expensive process of trial and error. Big time consumer. But if you're into inventing maybe it would be fun.
My experience with diesel electric has been with much bigger vessels. While it can be more eficient there in you application it will be considerably less efieicent than direct gas engine drive.


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## steel (Sep 1, 2010)

If diesel consumes 60% as much fuel as gas then the generator, controller and motor has to be only 60% efficient to break even, which should be easy to beat.

And diesel is safer than gas 

But yeah if you're not the kind of person who likes to invent stuff and get something working without any instructions to follow this isn't for you.

Personally, I would really like to see someone try this.


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## Inconceivables (Dec 10, 2009)

Check out the current issue of good old boat. Atomic 4 repower to electric for $2000. For some, particularly day sailors on ligher boats who primarily use their auxiliary for docking, this is a viable and cost-effective solution. Others may not find the compromises appealing. I have been researching it for my boat, a C&C 35, Mark I, and think it would be cheaper than an A4 rebuild and, more importantly, going forward would require far fewer hours spent working on the engine rather than sailing. I lost most of last year to A4 issues and may lose all of this one too. I dont' have much on the boat other than a vhf and a gps, and I fall into the category of only using the engine for getting in and out of the marina so its intriguing for me, at least. The standard they say many aim for when designing a system is 4 hours at 4 knots. That may be okay for some, not for others. With a solar panel and regenerative recharging when sailing, it may be viable for short-range cruisers.


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## Mark F (Mar 7, 2006)

Hi Inconceivables,

I don't know what an A4 rebuild would cost but to repower with a "proper" electric auxiliary system I'm sure it would cost more. The electric setup in GOB article is a minimal one. This may work for some people but for me doubling the battery capacity to 200 amp hrs would be a prudent move.

The cost comparison of A4-EP is just scratching the surface. Electric propulsion on a sailboat is simply amazing. I have a 48 volt 4kw unit (SolidNav) with two 100 amp hr battery banks in my Ericson 27. I have motored for 7 hrs at 4knots on one of the banks. 

All the things you hear about lots of torque for docking, quiet motoring, no fumes, simplicity, always there when you need it really need to be experienced to be appreciated.

I've got $6000 into my electric auxiliary, just passed the three year mark and couldn't be more satisfied.


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## Inconceivables (Dec 10, 2009)

Glad to hear it, I am getting closer to pulling the trigger any day now. I have been quickly discovering how hard it is to hold the line on costs and agree that $2,000 is not in the cards, particularly for a system to push a larger boat. One item that I see discussed vaguely but can't seem to get any information about is a gearbox/speed reducer to lower the rpm of the electric motor to a proper shaft speed. I've left a message with one motor company and have been trying to do web research but I'm not finding anything off the shelf. Is this a custom order item? About what would it cost? The recommendation is a 2 or 3:1 reducer for a motor rated at 15hp and 3700 rpm. Thanks.


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## nickmerc (Nov 2, 2008)

I have been planning my system for about a year now. My A4 is still running strong so I have not pulled the trigger. To reduce the motor speed you can use a gearbox as suggested in the GOB article. However, I would suggest using a timing (synchronous) belt drive. It is very light consisting of only a frame to mount the motor over the shaft, 2 or 3 aluminum (other materials are also common) pulleys depending on how you want to tension the system, and a single timing belt. Also the efficiency is conservatively 95%, more likely 97% - 98%. And it is easy to change your gearing ratio if you do not like it. The pulleys and belt are off the shelf items and can be found at any industrial supply website.

You want your gear ratio to have the prop spinning at it's max rpm when the electric motor is at about 90% of it's max rpm. If you have other questions about this, please PM me.


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## P35juniper (Feb 11, 2010)

The best way to get the RPMs right is to get a motor that runs at that speed and direct drive it, if you are going with an AC system you can get 6 pole motors that run at 1200 RPM. If a DC then a motor that runs at the desired RPM at the voltage you want to run at, as DC is RPM/volt. 
Horsepower is another can of worms, gas, diesel, AC, DC, are all different, engines are what it will make and still keep rpms, motors are what it will take to overheat, some 5 HP DC motors can make 50 HP for a few seconds, 20HP for minutes, 10 HP for 1/2 hour, and 5 HP for ever.


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