you are right, gould. prop walk in forward would be starboard because the prop
is turning cw as viewed from behind.

btw, Chapman's is correct as far as asym thrust is concerned, but end-plate
effect would add to the total lateral force.

assumptions as given, yes.


"T-boned to a dock"?

Assumptions:

1. You are describing a boat with a rh prop.

2. "T-boned to a dock" means the stem is jammed against the dock to prevent
forward movement.......(until the stern swings far enough that the angle is
no
longer sufficient to brake the boat).

With those assumptions...........

Q: Which way does the stern of a boat t-boned to a dock turn when, with the
rudder turned to port and the tranny in forward, you give a 2 second burst
of
the engine?

A: I think we all agree the stern will move starboard.

(you mean a two second application of forward gear, as the engine remains at
least idling, but otherwise......)

Correct.




Q: same question but rudder turned to starboard?

A: the stern will move to port.

Correct


Q: same question but rudder centered?

A: the stern will move to port due to prop walk

Incorrect. Here are some excerpts from my old copy of Chapman's. We can
probably assume that propellers still behave the way they did 20 years ago.

"Another factor also effects a boat's readtion to propeller rotation. While
this factgor is sometimes referred to as 'sideways blade pressure' it is
more
properly an 'unequal blade thrust', exerted by the ascending and descending
blades of the propeller. Figure 709, top.

Here we are looking at the starboard side of a propeller shaft, inclined, as
most shafts are, at a significant angle to the water's surface and the the
flow
of water past the blades. The actual pitch of the blades as manufactured, of
course, is the same, but the water flows diagonally across the plane in which
the blades revolve.

Figure 709 shows clearly how the effectof this is to increase the pitch of
the
descending starboard blade, (right hand propeller) as compared with the
ascending port blade, when considered relative to the direction of water flow
past the propeller.

The importance of this factor is reduced as the shaft angle is decreased, and
naval architects sometimes take pains to have the engine installed as low as
possible to keep the shaft nearly parallel to the water's surface and to the
flow of water past the blades. This contributes to greater propeller
eficiency,
and is a factor worth considering if it is consistent with other design
requirements. Once a boat is built, shaft angle is difficult, usually
impossible, to modify.

The relatively greater blade pitch on the starboard side creates a stronger
thrust on this side, causing the bow to turn to port.
As far as this single factor is concerned, THE STERN OF A SINGLE-SCREW BOAT
WITH A RIGHT-HAND PROPELLER
THUS NATURALLY TENDS TO GO TO STARBOARD WHEN THE PROPELLER IS GOING AHEAD,
AND
TO PORT WHEN IT IS REVERSING."


Q: same question, rudder centered, but tranny in reverse (bow of boat tied
to
dock)?

A: the stern will move to port due to prop walk


Correct.





Q: same question (tranny in reverse) but rudder to port?

A: the stern will move to port due to prop walk

Correct, particularly when the bow is secured to the dock and the vessel
cannot
develop sternway.


Q: same question (tranny in reverse) but rudder to starboard?

A: the stern will move to port due to prop walk




Anybody but sherr doubt that?

Chapman's, for one.
According to an indpendent and recognized authority, you only missed one.
That
gives you what, a strong B? :-)

JAXAshby wrote in message
...
you are right, gould. prop walk in forward would be starboard
because the prop
is turning cw as viewed from behind.

btw, Chapman's is correct as far as asym thrust is concerned,
but end-plate
effect would add to the total lateral force.

In your language - a flip flop?

I seem to remember about a week ago that I challenged your
explanation of prop walk (the aeronautical simile) with a bit of
trig to point out that the asymmetric thrust effect is
insignificant compared to hull interference (you call it end
plate effect?).

What I missed, in fact, is that it is even in the opposite sense!

JimB

no, jim, what you see was quick typing on my part. "prop walk" is always to
port (on my boat, a rh prop) because I only worry about it when backing up.
Going forward I use the rudder to counter, something I can not do when backing
up until the boat is moving. I typed the tranny in forward and just typed prop
walk port. In forward, the prop walk is starboard.

quick typing, that's all. asym thrust is asym thrust. someone even quoted
Chapmans on the issue.

you are right, gould. prop walk in forward would be starboard
because the prop
is turning cw as viewed from behind.

btw, Chapman's is correct as far as asym thrust is concerned,
but end-plate
effect would add to the total lateral force.

In your language - a flip flop?

I seem to remember about a week ago that I challenged your
explanation of prop walk (the aeronautical simile) with a bit of
trig to point out that the asymmetric thrust effect is
insignificant compared to hull interference (you call it end
plate effect?).

What I missed, in fact, is that it is even in the opposite sense!

JimB