For the first part of this response, I'll comment on some specific
items, as they are side issues.
For the part on "propwalk theory", I'm stepping back and taking a look,
because as Shen has said our major stumbling block revolves around "prop
efficiency" at certain angles and our individual visualization of what's
occurring.

Steven Shelikoff wrote:

The pivot point has changed position. Now, rather than being @1/3rd of
the way from the bow, it's @1/3rd of the way forward of the stern.


Doesn't matter. It's still within the confines of the boat.

It mainly matters in a sense of maneuvering to visualize the point about
which the boat is turning, so you can understand what is happening at
each end. I find a number of people who understand the 1/3 aft for
ahead, but forget to change this to 1/3 forward, for astern.


But this is not true in reverse since you don't have the propwash going
over the rudder.

You don't have the propwash over the rudder, but you still have the
"propwalk steering component" which can turn the boat more easily and
sooner than the astern thrust can start moving the mass of the boat astern.


How many blades does the prop you're watching have? If it's one or two
then maybe you're not being fooled. If it's 3 or more, especially if
it's 4 or more, then you can't separate what you think you may be seeing
one blade doing from what the rest are doing because they are too close
to each other in angle. For instance, if you're watching a 4 blade
prop, what "splashing" you think you're seeing from the blade at TDC
starting to move over and down could just as easily be from the blade at
270 and starting to come up and over.

They're apt to have anywhere from 3-6. This view has occurred over many
years, watching many props, some on diesels some on steam turbine
(sitting on a dock watch the warm up spinning of the prop fwd and astern).
You need to remember, these are props with @ 25' diameters turning,
initially at maybe 15-30 RPM.
G Call me an oddball for standing there watching/studying this, but
then again, I like watch porpoise swim in the bow wave and seeing how
they move with it.

On to propwalk ....

In reading the last few post, it's obvious we are now just chasing each
other in circles and resolving nothing.
A main issue is prop efficiency at various angles of rotation.
My opinion:
For a boat floating on the surface, when discussing prop efficiency we
must consider that the prop is affecting two mediums -water and air.
The prop is at maximum efficiency when it is affecting water alone and
at less than maximum efficiency when it affects air and water.
Is the depth of the hub of the prop important? To a degree, yes, but for
the boats we are discussing, the effect is constant, it's degree varies.
For instance, hub at surface half of prop out of water (Arneson drive);
blade tip at surface, hub submerged; blade totally submerged..... the
blade is more efficient, overall, in one semicircle, than the other, in
all of these conditions, in my opinion.
During the rotation of the blade, it is my opinion that the blade is at
the most maximum efficiency between the angles 045* and 225* of rotation
because it is acting against only the single not compressible medium of
water.
However, between the angles 225* and 045* the blade is operating at LESS
than maximum efficiency because it is acting upon both water AND air.

BG Until we resolve this issue between us, we are just butting
heads.....and I'm running low on paper ....

otn