ct: Which way does a boat turn?
From: "Scott Vernon"

My feeling is that you have to get that prop down really deep (as in submarine)
before this doesn't apply.
As another visual .... next time you back down (and for this purpose start DIW)
and start going astern look at your prop wash.
You should notice two things about it.
First, on a high percentage of single screw boats, the majority of the
disturbed wash you see at the surface will be coming out from underneath the
stbd side of your hull (you may see little or none on the port).
Second, that disturbed wash is getting to the surface ... lifting against air.
It's not the difference in depth between the top and bottom of your blade, it's
the difference in what they "push" against or towards.
The fact that the boat is attop of it doesn't really matter. Many hulls angle
up both astern and to the sides, and the wash, generally doesn't have to go far
before it is free from the hull and can lift into the air (same end results).
Mind you, I have no studies or scientific treatise backing me up on this ....
this is just my own observation and sense of what I'm seeing and why, coupled
with statements from a good number of older wiser boat handlers.

Shen

Yes, I understood where you were going with this. I agree, with the paddle
wheel slightly out of the water, to a little (6'') below, but what about a
sailboat prop, 1' below the water with a boat sitting on top of it. And with
the smaller dia. blade on a S/V there isn't much depth difference between
top and bottom blade. Although even a miniscule difference could account for
prop walk given the RPMs of a small blade?

SV