That was a good explanation and I got what you're trying to say. The
only problem with it is the overhang. My prop is about 3 ft down. The
clearance to the hull above it is around 3 to 4 inches. There's still
about 5 or 6 feet of waterline behind the prop. So on the upward
stroke, the blade is pushing the water column against the hull.

First, what is the shape of your hull? Secondly, look at the pitch of your prop
- the main push is back, the "UP" angle is only slight and not directly "up"
against you hull, even WITH (I'll bet) 5-6' of overhang.
Even in reverse, with any degree of deadrise, the push to the side and up will
not be mainly impacting on your hull for the full revolution, if at all, and
even if you have no deadrise, the water will shortly leave the confines of your
hull and be allowed to push up into the air.

Not
only is there no noticable bulge of water behind the boat from the prop
but there isn't even a sign on the surface that there's a prop turning
at all. I just don't get that stream of bubbles behind me or a bulge in
the water that powerboats get or anything other than the same sort of
wake I get when sailing. And yet there's pronounced prop walk when
reversing.

Steve

My feeling on this is that the visual effects of prop thrust are not always
readily apparent, but this does not in and of itself, alter what is occurring,
i.e., you don't need a big white water wash, astern or ahead of you to be, in
reality, experiencing a lessor degree of efficiency from the prop during half
(maybe a little less, maybe a little more) of it's rotation, which is causing
the unequal pull to stbd or port, depending on it's rotation.

Shen