Re: sailing upwind?

[brian whatcott <inet@INTELLISYS.NET>]

At 19:52 12/30/99 -0500, Ludwik wrote:
> ... 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


Although Ludwick did not mention it, his air propellor is at the
rear of the craft and the water prop is a tractor up front.
This provides an 'into wind' turning moment.

 In interesting previous threads about the propulsive force on
rockets and airplanes called 'thrust' we decided that thrust could
be associated with ANY change in momentum provided by ejecting
exhaust or accelerating the air column through a prop.

    In this case, the momentum decrease from the air prop must
equal the momentum gain at the water prop - giving no net thrust.


brian whatcott <inet@intellisys.net>
Altus OK