My thoughts for what it is worth is the 15 kw motor is far more power than you can utilize but should easily take you to hull speed at light load. I had a 23 foot well craft cruiser (aprox 6000 lbs). At idle (600 RPM) the boat wanted to go 5 MPH with noticeable bow rise (hull speed +). I installed 2 X 50 lb thrust trolling motors for maneuvering (never intended as main power) and got good low speed thrust with a max speed of 3 MPH. Wild guess 1 to 1 1/2 kw. This suggested that gearing the input rpm of the outdrive to 800 rpm would give it a high top speed and power to fight wind and current without wasting power trying to get on plane. Mine required all 250 hp gas to get up. Use your experience with idle RPM and MPH to get your own numbers. Remember to remove the water pump impeller. I don't think there is a huge disadvantage to running a 15 kw motor at 5kw load, with higher RPM for cooler running. The only disadvantage I see with this type of hull is efficiency for battery range but I don't know if anyone has measured this. A previous poster extended the aft portion of his planing boat hull to resemble a more displacement like form which might help. I was planning to try this with a 5kw install but got a lifeboat hull instead and am working on this. My 27 foot lifeboat has less floor space than my 23 foot cruiser. Sailboat hulls have even less internal space per foot and I have read tend to be a little tippy initially but are more stable leaned over. I was very happy with the electric driving the cruiser and would not discourage your project. It would be nice to get some range/power requirement data for small converted cruisers.
Posted by: marvinwiens@yahoo.com
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