Preston,
I do not have an electric propulsion system, so you may want to take my advice with a grain of salt. However, I am an electrical engineer, so I know something about creating electrical systems that work. Perhaps my comments will nudge other responses.
Since you want to power a fairly large sailboat and since you are removing an inboard motor, I would recommend a 10-20hp electric motor. To get that kind of power requires at least 48 volts, or one bank of four 12V batteries. The principle for voltage selection is: the higher the voltage, the lower the current. Large currents can require more copper than is practical. The best connection to the propeller is an AC motor with a motor controller. The input to the motor controller is DC, but you get the advantage of a reliable brushless motor and more importantly, speed control.
There are a lot of tradeoffs with regard to how many banks you need (adds Ah) and how fast you can recharge those banks. At least you will need a charger that connects to shore power. If you already have a device that changes AC to charging DC, an AC gen set is probably the best way to avoid duplication of equipment. If you choose the charger carefully (make sure the manual says you can connect other electrical equipment while it is charging), then you can use the power from the gen set/charger to run the motor. In this case, the batteries keep the charger from shutting down (which it would do if it did not detect a minimum voltage), but the current from the charger is used to power the motor. It makes sense to me to approximately match the charger output (volts * amps = watts) with the cruising volts * amps needed by the motor.
Gary
---In electricboats@yahoogroups.com, <electricboats@yahoogroups.com> wrote:
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