Hans,
You are assuming he will need 20KW to get 6KT, but is that realistic? Is there any available data on power requirements for that hull (or something similar operated well below hull speed? It seems obvious that something designed for displacement speeds will be more efficient, but since there are so many more "non-displacement" boats out there it might be worth some research. A simple tow-test could establish the drag numbers (thrust requirements) and a little number crunching will get you the HP requirements.
Jim McMillan
--- In electricboats@yahoogroups.com, Hans Rijnbout <jrijnb@...> wrote:
>
> Stephan Hinni wrote:
>
> My idea is to use the yacht for scuba diving and pleasure trips. I'd
> like to cruise at 6 to 8 knots and have a daily range from 40
> nautical miles.
> I want to use two 10 kW Mars Motors and let them run at 72 Volts.
> Battery storage is no problem once the gas engines are out! The
> battery charging is at the slip (110V) and while navigating 4 Solar
> Panels bring in a bit of extra amperes. A gas generator is on board
> too but it have to be fixed first.
>
> The yacht is currently powered by 2 Chrysler 250HP gas engines. The
> length is 30.4 ft, breadth is 12.8 ft and she weights 16000 lbs. The
> propellers are 16RH16 and 16LH16 and the gear ratio is 1.52:1.
>
>
> Even with some added weight from the batteries your boat should run
> at about 6 knots at 20 kW power.
> So 40 miles take 7 hours, using 7*20 = 140 kWh net energy. With
> lead-acid batteries at 50% depth of discharge this would add around
> 15000 lbs to the weight, so this does not look realistic. Lithium
> batteries at about 80 or 90% d.o.d. would weigh in at around 4000
> lbs and would cost you a small fortune.
>
> --
> Hans Rijnbout
> Utrecht, Netherlands
>
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