On Tue, 23 Nov 2010 12:20:43 -0600, CaveLamb
wrote:

Joe wrote:

Have been on a hundred boats with 25-72 inch props and had to chain
them down many times to prevent damage to the gears. As I said the
power is massive and you had better have heavy chains and binders.

Joe





There is no doubt that the prop will turn (or at lest want to) when
water flows past it.

But to develop any real power, the pitch of the blades has to change.
Think about it from the POV of the propeller.
When running and moving the boat, the prop attacks the water stream
at a fairly fine angle. Spinning, the prop takes a small bite of
water and sends it aft. Water meets the prop a small angle off of
the leading edge.

When not running, and just dragging through the water, the angle of
attack is huge. Water hits nearly flat on the face of the blades.

If you want to use the prop to generate electricity, to have any
kind of efficiency, and reduce drag, the prop blades need to change
pitch by about 90 degrees.

And all that just to reduce mechanical and speed losses to minimum.
They WILL still be there.


Some people seem to think that since it's a sailboat, and slow anyway,
that a little loss of speed is ok.

I'm of the other mind. Since it's already slow any additional losses
are unacceptable.

(trim yer sails, mate)


A lot of information on turbine water power at
http://en.wikipedia.org/wiki/Water_turbine
and apparently it is not "new technology" as the Romans used the
concept.

Cheers,

Brice