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Re: sailing upwind?

brian whatcott wrote:

... But Leigh's windmill propulsion seems to demand only
that the superstructure and air prop drag due to the wind is
less than the water prop thrust due to power from the air
prop. Some positive net force will provide headway even
into the teeth of the wind. ...

Sounds like a perpetual motion of the second kind. My brain
will need a working model to be convinced that the net force
can be positive here. I know that sails were used to construct
windmills; perhaps the opposite was also tried by some inventors.

The question brings to mind the experimentally confirmed
fact that an air blower situated on a deck and blowing into
the sail can provide net forward thrust too.

I have a very effective classroom demonstration of this. But
the blower is electrically operated. The direction of the net
force depends on the distance between the propeller and the
rigid "wind reflector".
Ludwik Kowalski