"Edgar" wrote in message
...

troll sh*t removed
That is the easy answer that seems to satisfy most people but if you think
about it do you really believe that water gets measurably denser because
it is about 18" (say) deeper at the bottom of an 18"(say) propeller than
the water at the top? Of course it does not. Water is hardly compressible
at all except at very high pressures.
. Density will only be a factor if air is being entrained from the
surface.
You will find boats displaying propeller walk even if the propeller is too
deep for air entrainment to occur. My boat does.
So the question is 'why does the opposite direction of the blade at the
top not cancel the walk created by the blade at the bottom'?
I suggest that this is because as the blades rise upward towards the top
the water impinges on the hull and creates a reaction force which acts in
the same direction as the walk force created at the bottom. This is
because, in yachts especially, the blades pass very close to the hull
which usually is somewhat vee shaped and deflects the water sideways. In
your example water would be deflected to port but the reaction on the hull
would be a starboard force.



Think hydrostatic pressure. Also, Neal is wrong.

--
"j" ganz @@
www.sailnow.com