Steven Shelikoff wrote:
On Mon, 07 Jun 2004 15:52:25 GMT, otnmbrd wrote:


As for the "overhang" of the hull,issue, look again at the pitch of the
blade. When the blade is pushing up/back, it's not straight up, it's G
BACK/up, then look at the wash astern of your boat .... you'll see it
breaking the surface astern of you.


Not on my boat. There's still maybe 5 feet of boat hull in the water
above the prop behind where the prop exits. There's no prop wash at all
breaking the surface astern of me. And since we're talking about
backing up from standing still, there really is nothing of the sort
you've described above. And yet I still get prop walk.

Steve

G There's always the boat which doesn't appear to show the obvious
reaction.
Considering the angle of pitch of the prop, when ahead, 5 feet is
relatively nothing..... also, what is the shape of your hull aft of the
prop?
I've seen the same results, but my feeling is it takes very little
"lift" of the wash from the prop blade to create that unequal thrust
back and to the side, we know as "propwalk".
You are saying there's nothing of the sort that I've described. I'm
saying it's not always readily apparent, but it IS there.
Back a boat from a dead start .... you won't immediately see the wash.
Back a boat that has headway .... it will be even longer before you see
the wash .... but .... the unequal thrust WILL be occurring.
If you have a low power to weight ratio, the visual results will be
greatly lessened. However, this does not mean they aren't occurring.
Again, BG I'm no scientist, engineer, Naval architect, or prop
designer .... my opinions have developed over a good many years of
talking to individuals, handling all kinds of boats, watching wakes and
reactions .... the "root" cause is prop rotation .... everything else is
a variable, adding or detracting from the mix.

otn