Doing a Conversion from Diesel to Electric

[Breezzy]

Looking for others who have accomplished a Conversion to Electric. Just getting my boat, stating to do research and planning for this change over. Seems the rule of thumb is 3-hp needed for every ton, so approx. 20-tons that is 60-hp. Should I go with a PMAC or? what is the best setup for a 20-ton Conversion?
Thanks, Thomas

 

[JohnShannon]

What are you hoping to achieve? The knock on electric is ... range. Most boat shows will have one or other electric motor purveyor.

 

[VanIslandGuy]

Interesting discussion from three couples who have done it. Not for me, I like range and speed under power as I might only have three or four days off to sail between work periods, but I can see the appeal. Less noise, no smells, no oil changes, exhaust elbows, smoke diagnosis, coolant changes, etc.

 

[Brian M H23]

I read somewhere, people are using BMW hybrid batteries. By some simple calculations, something like below would run a ~ 30 hp motor for 10 hours. Probably weighs 600+ lbs, without any drive train.

 

[Sailm8]

I personally can't imagine having only 5 or 6 hours of cruising under power. I'm already paranoid about "only" having 20 gallons of diesel. I have been following "Sailing Uma" on you tube. They have converted to electric with the understanding they will need to overnight (maybe more) everytime they motor in order the charge up.

 

[Will Gilmore]

Electric doesn't convert directly from fossil fueled motors, in terms of power. Electric motors have a more linear power curve so it often takes less overall HP with electric than a combustion engine.
I don't know why the range has to be limited either. It may be more expensive to buy the battery power supply, but you can refuel in the middle of the ocean with wind and solar. Can't do that with diesel. You can also setup for reclamation power generation by letting your prop spin while sailing. The electric motor becomes a dynamo power generator. You're dragging the prop through the water anyway, get that energy back.

-Will (Dragonfly)

 

[Will Gilmore]

A quick Google search shows an acceptable conversion of a little better than 2:1 for electric hp motors from diesel hp motors. Electric motors have nearly the same torque at the low end as the high end and their power gets directly transferred to the prop (about 90%), where diesel motors are rated by their high end hp output only and there is over 50% loss of energy before the prop (I've read as much as 70%).
There is huge misconceptions out there around electric motors. Lots of gearheads don't get the concept of direct drive, so they miss the whole 90% efficiency vs 35% efficiency and the flat torque curve idea.
Here are a couple of the forums I looked at.
https://www.glen-l.com/phpBB2/viewtopic.php?t=5704

https://www.boatdesign.net/threads/how-do-you-compare-electric-motor-power-to-diesel-power.41038/

BTDubs, I'm putting electric on my boat, so I've been looking at this for a while.

-Will (Dragonfly)

 

[kloudie1]

I disagree with the concept of the 2:1 turndown.. A horsepower is defined as 550 foot pounds per second.. it is the same definition no matter what produces the power.. A 10 horsepower electric motor cannot make 20 horsepower.. many folks are happy with the performance of a smaller electric motor rating but that electric motor at a 2:1 turndown cannot match the diesel (or steam or gasoline etc) for ultimate power at the propeller.. Part B: most folks who talk efficiency of the electric motor being much greater than internal combustion forget to include losses in the wires, connections, and in the motor controller and in the chemistry of "making" electricity inside the battery itself.. Yes, diesels aren't as efficient as electrics but the difference is exaggerated by folks wanting to sell them. To folks who are happy with them, I say GREAT.
The marine diesels are rated at the propeller shaft .. and at an RPM that is "continuous allowable" .. you can run it that way all the time..

 

[Brian M H23]

Kloud has a good point
Running a 60 HP electric at 60 HP for many hours requires significant cooling of both motor, controller, and battery, using 000 conductors. It's a far more complex and far-reaching system than simply keeping the engine block of a 60hp diesel acceptable.

 

[SG]

I have a friend that essentially de-dieseled his sailboat and put an electric drive in it. (38' boat). He's is an engineer by training, a brilliant guy, and a someone that I've sailed a bunch of offshore miles with. He "sort-of" lives on his boat.

It was an idea that almost all of his friends tried to talk him out. He wishes he'd listened.

 

[dLj]

I think one of the main points brought up in the video was talking about Lin and Larry Pardy running without a motor and comparing that to running with an electric motor. It seems that the electric motor in a sailboat is more inline with using it instead of oars, or other human powered propulsion. There is no real comparison to running a diesel engine.

Just my 2 cents worth...

dj

 

[Gunni]

The guy who charted most of the Windwards over decades, Don Street (Imray-Iolaire) did so on an engineless 100year old boat , and did a number of trans-Atlantics. He used a tafrail hydrogenerator to meet his electric needs. Basically, if you can sail a boat, you can make electricity. Whether that is enough to run an electric motor in the manner you use the boat, is another matter. Displacement cruisers are a great application for diesel propulsion - the engine is run at high load for prolonged periods. If you are just going daysailing and need a motor to get you to open water and back to the slip, an electric propulsion motor is a good option.

 

[jssailem]

The couples in the video, claimed they converted because they "wanted to" not as a replacement for a diesel engine. Two of the couples bought boats with non working diesels. The third was given a boat and removed the diesel to replace it because of smell and the idea of being "fossil fuel free". It has been said... Boats are series of compromises.

All of them agreed: "the electric motor does not replace the diesel it replaces an oar". "You have a primary power source to move the boat - the sails. We want to use the sails."

If you have plenty of time you can be like the Lin and Larry, just sail up to the anchorage and drop the sails.Then get in the dinghy and row to shore. If you want to visit a marina dock or get through a 5.5 knot tidal passage, not having to wait for 6 hours, then electric is for lights not powering your boat.

That does not make you a "Bad person" because your using fossil fuels. It is a choice.