Repowering with and electric engine?

[rpwillia]

One problem I have heard about generators on boats is they do not get used enough and tend to have problems due to that. Is it possible to get a boat with two generators that could drive an electric motor to get you up to speed and then have a generator and a backup for when you are on the hook? Generators are pretty quiet and in that way you would have more flexibility. You could also avoid the investment in batteries. If you did not need full speed you only run one generator. Have not done the math, but it seems like that would be a better combination that some of the bigger boats that have a main propulsion motor and a generator installed. Downside would be that the control system needs to be more complex and you would have to equal our the hours on both engines.

 

[Msweetnam]

One problem I have heard about generators on boats is they do not get used enough and tend to have problems due to that. Is it possible to get a boat with two generators that could drive an electric motor to get you up to speed and then have a generator and a backup for when you are on the hook? Generators are pretty quiet and in that way you would have more flexibility. You could also avoid the investment in batteries. If you did not need full speed you only run one generator. Have not done the math, but it seems like that would be a better combination that some of the bigger boats that have a main propulsion motor and a generator installed. Downside would be that the control system needs to be more complex and you would have to equal our the hours on both engines.

I think the short answer is no, assuming you want your electic motor to have the same power as your engine. Your generators would have to put out the same amount of energy as the electric motor uses plus cover the inefficiencies in the system (converting gasoline to electricity to charge the battery storage mainly). So unless the electric motor is much less powerful than the engine it's replacing, or is much more effecient, your idea would actually take more fuel to run the generators. Cheers.

 

[tfox2069]

Interesting thread. Sailing Uma converted to electric power for long range sailing, and they have an excellent laydown of their thinking here:

Sailing Uma— THE MOTOR

There's also some links to vendor information on electric installs that is pretty interesting. For example, Annapolis hybrid Marine estimates that you can nearly DOUBLE the battery usage time by dropping from 3 knots to 2.5 knots. Yeah, that's excruciating, but an interesting pointer to how much power it takes to push a displacement hull through the water at different speeds.