gould, you are right *IF* the boat is moving. However, not right if the boat
is not moving.

We agree.

I took issue with your statement:

Let me help you out here. a rudder has NO effect on which way a boat is
going
in reserve because of the prop.

because the phrase "which way a boat is going in reserve (sic)" implies the
boat is in motion. Rather obviously, if the boat is going somewhere, it must be
in motion.

Putting the boat in reverse will (after a split second) result in sternway
unless the engine is not running
or the vessel is lashed to the dock. When the sternway becomes sufficient, the
rudder exerts greater influence on the direction of boat than the prop walk
does.
In my experience. Unlike some here I don't have a string of degrees and
abbreviations following my name, (unless S.O.B. counts), so I can't argue the
applicable theories of physics or fluid dynamics....... but by the same token I
don't have to conduct an "experiment" to know how a single screw with a fair
size rudder behaves in reverse. :-)