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Re: sailing upwind?



Last night Leigh wrote:

Isn't it possible, in principle, to "sail" directly into the wind by
driving a (submerged) propeller with a wind-driven turbine? It seems
to me that, while somewhat inelegant, there is no reason this should
not be possible. Energy is extracted from the airstream (it is slowed)
and used to overcome wind resistance.

To learn from those who know better I will end this message
with a specific question. Here is a situation. A wooden block
floats in a narrow channel (ice on each side confines its motion
to a single dimension). A hole is drilled and a drinking straw is
inserted into it (at about 30 degrees with respect to the horizontal).
One end of the straw sticks up, the other is immersed in water.
A shaft is introduced into the straw and it can spin without too
much friction. The immersed end of the shaft has a propeller screw
mounted, it is located behind the boat. A set of large twisted blades
(call it a windmill) is mounted at the upper end of the shaft.

This is probably the most primitive attempt to construct a device
described last night by Leigh. One shaft and two sets of twisted
blades. There are no gears, the rpm of the windmill and the rpm of
the immersed screw are identical. I guess there are valid theoretical
arguments for not even trying this simple arrangement. By itself it
will never advance directly into the wind. What are these arguments?
Ludwik Kowalski