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Old 09-12-2013, 10:45   #1
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Conversion to Electric Motor

Hello,

I am interested in getting rid of my 35 HP diesel engine in my sailboat and swapping for an electric of around the same power.

What am I looking at in terms of parts and cost? I know I would need the engine, batteries (how many?), and solar/wind generators. Anything else?

Anyone here who has done this conversion, please let me know about your experience.

Thanks!
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Old 09-12-2013, 11:17   #2
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Re: Conversion to Electric Motor

This pdf may help with the calculation you will need.

Here is a good site for electric motors also.

http://www.goldenmotor.com/
Attached Files
File Type: pdf Diesel_Engine_Replacement.pdf (107.9 KB, 483 views)
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Old 09-12-2013, 11:42   #3
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Re: Conversion to Electric Motor

The subject has been visited on several occasions. Here's one: Electric Sailboat . . . On The Cheap ?
Do a search in the search engine and you'll find plenty of others.
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Old 09-12-2013, 11:45   #4
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Re: Conversion to Electric Motor

Here's the one I'm familiar with:
Electric Propulsion
Still doesn't have the range of a diesel.
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Old 09-12-2013, 12:31   #5
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Re: Conversion to Electric Motor

Phase,

It is all about range. There is no way to store enough energy on a boat except in the form of gas/diesel to have close to the same range.

As a rough guide, one pound of diesel has as much usable power as 50lbs of batteries. So a 20 gallon diesel tank that weighs about 120lbs full would require about 6,000lbs of batteries.

Assuming you are ok with very short motoring ranges at low speed it is doable, but that's about it.
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Old 09-12-2013, 12:35   #6
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Re: Conversion to Electric Motor

Thanks for the information. It is looking like converting my current diesel into a hybrid would be the best option. There is a kit that allows to you slap on a hybrid system direct to your current diesel engine.

I dominantly only see myself using the motor for getting in/out of the marina at this point...but that might be a bit optimistic.

http://www.hybrid-marine.co.uk/5.html
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Old 09-12-2013, 12:59   #7
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Re: Conversion to Electric Motor

In addition to the issue with range, if you buy a commercial, off the shelf marine system that will give you power equivalent to your current diesel, expect to pay at least 50% more than installing a new diesel. I have price several systems at double the cost of a new engine AND transmission.

Then you have to figure out a way to keep the batteries charged. Obviously can't install an alternator on the electric motor and generate electricity to run itself (if you do figure out how to do that please let me know the details). So now you have to install solar and/or wind or plug into shore power every night or install a generator.
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Old 09-12-2013, 13:27   #8
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Re: Conversion to Electric Motor

The manufacture and shipping of all that new stuff (batteries, engines, solar panels) emits a whole lot more CO2 than you'll ever emit using your existing diesel to get in an out of marina slips.
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Old 09-12-2013, 13:33   #9
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Re: Conversion to Electric Motor

Had a friend who bought a boat from Austria on a lake where combustion engines are banned. Nice setup but he had to run a generator to keep the batteries topped up .... Sort of defeats the object if you ask me....
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Old 09-12-2013, 13:37   #10
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This remains a challenging proposition.

There are some fuel cell options which show great promise but they of course will need fuel of some sort. Solar and wind and battery storage for propulsion need more real estate than is available on most boats.

The energy density of diesel and the cost by any practical measure are hard to beat.

I like the idea of an electric option inline betwen the transmission and prop. Redundancy if your engine or transmission fails.

Keep us abreast.
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Old 09-12-2013, 13:51   #11
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Re: Conversion to Electric Motor

Of course electric motors powered by generators have long been used on large ships, locomotives, and other transport. It is appealing, the idea of a relatively small motor turning the prop, and a remote small diesel generator with easy access and power for all electrical systems. But is anything like that available for yachts? Anybody know?
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Old 09-12-2013, 14:16   #12
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Re: Conversion to Electric Motor

Quote:
Originally Posted by Surrymark View Post
Of course electric motors powered by generators have long been used on large ships, locomotives, and other transport. It is appealing, the idea of a relatively small motor turning the prop, and a remote small diesel generator with easy access and power for all electrical systems. But is anything like that available for yachts? Anybody know?
Diesel electric systems work, but they have limitations... The ideal for a boat would be to have one generator that could do duty for both power generation and house loads... The problem is that the power demands for each system are radically different.

A large complicated boat may use 7kw of power to run all the house loads at a time. Which seems like a pretty substantial generator right?

A typical 40' cruising boat has a ~40hp engine, which works out to a 30kw generator. Add in efficiency loss issues and you are talking about a 35kw generator to drive a propulsion engine on most boats.

The problem is that a 7kw generator isn't big enough to power an electric motor the boat would need, and a 35kw generator is too large to power the house loads. There are three ways around this, each with their own problems...

1) a very large battery bank with the smaller generator which allows the generator to supplement the bank when running the motor

2) a very large battery bank with the large generator. The house pulls down the batteries from an inverter, and we run the big generator to either power propulsion or to recharge the batteries.

3) a very large battery bank with a mid sized generator. Like 1) but it allows some operational freedom since propulsion can be run direct from the generator at a reduced speed. And while running house loads from the generator a large percentage of the power can be dumped into the batteries

The problem is that no matter what we do you need huge battery banks. Weighing thousands of pounds along with complicated chargers, inverters, auto-start generators, ect... All to run the system.

And while all of this works, it is very expensive, and complicated.


Where this works is where the house loads and the propulsion loads are closer in size, or where there are large differences in needed propulsion power.

So a tug company recently went to diesel-electric. One huge electric motor with three diesel generators. The first generator is sized to the travel load needed by the tug itself, the second and third generators are kicked on based on the size of the tow. This allows them to scale the amount of available power based on demand. But it doesn't work for a sailboat very well, since three 9kw generators would cost a lot more than a 7kw generator and a 40hp motor.
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Old 09-12-2013, 14:37   #13
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I was going to point out a third option used by Submarines since before WWII, and that's multiple Gen's, that can be used for propulsion, or battery charging. Of course this is enormously complicated, expensive, and what does it solve?
Only way that I can see electric propulsion making sense is if your boat is faster than you want it to be when under sail power alone, that way you could use the electric motor to generate power to charge the batteries when under sail and the increase in drag and decrease in speed would be acceptable. Of course then you wouldn't need Diesel at all.
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Old 09-12-2013, 14:43   #14
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Re: Conversion to Electric Motor

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The manufacture and shipping of all that new stuff (batteries, engines, solar panels) emits a whole lot more CO2 than you'll ever emit using your existing diesel to get in an out of marina slips.
Idea is to be self sufficient and not use the diesel engine unless I have to. As for CO2 emissions manufacturing, by that logic then nothing will ever change because the demand for green energy won't be there to change it.
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Old 09-12-2013, 15:07   #15
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OP, please save yourself a bunch of heartache and go to the electric boats group at Yahoo! Discussing electric propulsion here is a waste of time, a la the other threads.

I've converted a sailboat to electric. A Catalina 30, roughly 10,000 lbs. A good rule of thumb for electric auxiliary power is 1 KW per ton for capacity planning. That's continuous duty, not a short run (a lot of manufacturers rate on short unloaded runs in a lab).

Ignore anyone without hard data. People making numbers up doesn't count. That's why the electricboats list is so valuable. Actual experience. You can't compare ICE and electric directly, it's like comparing apples and band saws.

Electric is awesome, if it works for you. But there are some serious drawbacks depending on your intended usage and mindset. It's definitely not for everyone, but it's a decision that should be made based on facts and not fiction.

JRM

-- I'd love to convert our big boat to electric hybrid, but it just doesn't make economic sense at this point. Even as an avowed electric proponent, there are times it just doesn't work.
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