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post #1 of Old 09-07-2012 Thread Starter
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Optimal propulsion system

I have what may be a slightly unusual problem. My wife loves to sail but hates it when I have to put on the engine. I mean really hates it. She would rather sail at 2 to 3 knots than motor at 5 knots.

For coastal sailing however motoring seems to be a pretty common necessity.
The alternative is to get into a strange harbor after dark and miss dinner and a slip assignment.

I'm thinking that an optimal system might be an electric drive system with battery capacity for about 5 hours. This battery bank would be mated to a gen-set that had the horsepower to drive the boat at max throttle.

The system would be reasonably simple.
Genset with charger connected to battery bank.
Batteries connected to electric motor.

During the day if the wind was light I could motor sail for a few hours. The motor would be so quiet no one would know.
In the afternoon while we were off the boat I would run the genset to charge the batteries (The genset would be insulated so its running would not be noticed by any other boats)
If I really had to run the genset to run the motor it would be big enough to do the job and I would just have to deal with the noise.
  • I know this is not a cheap solution. Probably double what a re power would cost.
  • It is also pretty complicated with lots of controllers and electronic controls.
  • It will be somewhat inefficient converting gen-set horsepower to electric instead of shaft power. I'm hoping that the built in inefficiency will be off-set somewhat by the fact that the the gen-set can be set to the most efficient rpm as opposed to a shaft driven motor where the rpm is used control the boat speed.

Weather I would be willing to pay for and actually build such a systems is another question but assuming the above usage what do you think?
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