[C38] Prop walk versus prop wash

[les]

On Fri, 2011-06-17 at 14:36 -0400, Dick Kilroy wrote:
> I agree with Larry ,wash is what comes out from the stern in forward, walk 
> is where the boat tries to steer itself when in gear, in  our case with the 
> 5424 serious port pull in reverse or probably any engine with the same 
> rotation.
Prop wash I was taught by the illustrious United States Navy is the
plume from the prop.  This applies to both water born props and airborne
props.  

	Prop walk basically only applies to water born props.  It is due to the
density of water (about 100x the density of air) causing the bottom of
the arc to have more resistance than the top arc.  This means the boat
is pushed away from the water on the bottom swing of the prop.  i.e.
turn the prop clockwise and the boat stern walks to the right.  Turn the
prop counter clockwise then the boat stern walks to the left.  Because
the prop wash encounters the rudder when we're going forward, the
additional lift and resistance created by the prop wash on the rudder
will partly over come the prop walk when going forward (but not too much
as we all know.)  Since the prop wash doesn't strike the rudder in
reverse, we all notice that the prop walk in reverse is much stronger.

Regards,
Les H