On Sat, 31 Oct 2009 07:12:33 +0700, Bruce
wrote:

Secondly because movement of
the electrical generating fields is required. The specification should
have been some amount of horsepower, which is really another way to
specify speed and torque.

Yes. I think a good starting point would be the power equations for a
falling water tuurbine which is an old established technology. As a
frame of reference, water falling 16 feet has a velocity of 32 feet
per second. A boat under sail at 6 kts has a velocity of about 10
feet per second (2.5 meters/sec).

The basic equation can be found he

http://ahec.org.in/Aboutus/plant.html

POWER (kW) = 5.9 x FLOW x HEAD

HEAD is the comparable height to produce a velocity of 10 ft/sec in a
falling body or about 1.5 feet (0.4 meters).

FLOW is equal to cubic meters of water per second which should be
roughly equal to the area swept by your prop times the velocity of the
water. Assuming the velocity is 2.5 meters/sec and the area swept by
your 20 inch prop (pi R ^2) is about .2 meters, then flow is about .5
cubic meters/sec.

Plugging back into the original equation we get:

KWs = 5.9 * .5 * .4 = 1.18 kw or about the same as a 100 amp
alternator at 12 volts or about 1.5 horsepower.