Finally got some paper, so's I could print out, sit back and read/view
the whole, as I find reading on the screen tends to "tunnel" my view.
As I said about 4-5 days ago, we've thoroughly thrashed and rehashed
this issue and are just chasing each other in circles.
Some final thoughts, and I'll bow out (G everyone sighing with relief).
I doubt you've ever watched a large ship prop being turned by steam as
they warm up the turbines, though you may have (from a distance) seen
some diesel ships start. I've watched both at very close range, for
years, and still do (Though I see few turbines anymore).
The effect is obvious, not only in what it shows, but in which blade
it's coming from .... you can't believe this .... ok ... on to the next
point.
My feeling of the basic cause of propwalk, is the rotation of the prop.
Overall, the efficiency of the prop between the 090-270 arc (where the
blade is pulling the boat to the right when going ahead) is greater than
it is between the 270-090 arc (when the blade is pulling the boat to the
left) .... repeat, overall.
Nothing which has been said here has altered that opinion/feeling.
This is the basic cause.
Other factors enter in, to increase, decrease, and even negate this affect.
For instance, Charles Low mentioned the wash from the prop, going astern
(btw everything considered is a RH fixed pitch prop), would push against
the hull, causing the stern to move to port. My response being that this
was not the cause, but a factor. My feeling here is that while the wash
is pushing the hull left, the prop is pulling the hull right .... one is
canceling out the other, while the opposite blade is pulling the hull
left and this adds to propwalk. ( the additional amount will depend
greatly on hull form.)
I've "backed" vessels in really deep water and not so deep water
.....propwalk is there with little relative difference. However, when you
back in really shallow water, all bets are off. Frequently you will find
yourself going either way, or not turning at all, but my feel is, if it
"does" back to port, it will be at an increased rate.
Naturally, the biggest contributors or negators (is that a word?) are
wind and current ..... either/or can totally change the direction in
which your stern will back.
These are my experiences, feelings, views, based on 50 years on the
water, handling a multitude of vessels of all types and in all
conditions of water depth, bottom type, weather, currents, etc., .......
BG Yours may vary, be different, etc.,..... ok .....

otn