[Gramp34]

Capnblu: Just had a thought how you can increase your motoring efficiency -- not at the engine, but at the prop.

Bigger diameter propellers are more efficient, but they take more torque to turn and turn more slowly.

If your supercharged engine produces its full power at lower RPM, your prop spins more slowly. To absorb the full horsepower at the lower speed you can either increase the pitch, or increase the diameter.

If you can swap the blades on your Maxprop for larger diameter (as long as it still fits under the boat), the overall efficiency goes up.

Being a feathering prop, larger diameter won't noticeably increase drag when sailing.

Dave Gerr's "Propeller Handbook" has all the calculations you'd ever like to attempt when working things out. One thing to check, though, is that the propeller shaft is large enough diameter for the greater torque.

Good luck,

Tim