I have it but it's on the boat, not available right now. I read it but
don't remember a discussion about what exactly causes prop walk. What
does it say?

Steve

That unequal blade thrust is the result of the difference in effective pitch
between the descending and ascending blade when a propeller is rotated on an
angle, (90 degrees from the angle at which the shaft exits the shaft log)
though a horizontally advancing medium (water under the boat).

(Page 143 in my 1985 edition, may be different in later versions)

Gould 0738 wrote:
I have it but it's on the boat, not available right now. I read it but
don't remember a discussion about what exactly causes prop walk. What
does it say?

Steve


That unequal blade thrust is the result of the difference in effective pitch
between the descending and ascending blade when a propeller is rotated on an
angle, (90 degrees from the angle at which the shaft exits the shaft log)
though a horizontally advancing medium (water under the boat).

(Page 143 in my 1985 edition, may be different in later versions)

Thanks Chuck. (Damn ... G more people are reading this thread than I
thought).
hmmmmm ... If I'm reading this correctly, Chapman is saying the shaft
must be angled "down" from the horizontal flow of water, and this is the
"root" cause?
UHOH. I disagree that an angle down or up for that matter, makes a
difference to the root cause. I do agree that it MAY increase propwalk.
I also agree that the main cause appears between the upward and downward
ascent of the blade, but feel that the main difference occurs between
090-180 and 270-360 ( eg I believe 180-270 is marginally more
efficient than 000-090).
Thanks again

otn

On 10 Jun 2004 02:08:17 GMT, (Gould 0738) wrote:

I have it but it's on the boat, not available right now. I read it but
don't remember a discussion about what exactly causes prop walk. What
does it say?

That unequal blade thrust is the result of the difference in effective pitch
between the descending and ascending blade when a propeller is rotated on an
angle, (90 degrees from the angle at which the shaft exits the shaft log)
though a horizontally advancing medium (water under the boat).

(Page 143 in my 1985 edition, may be different in later versions)

That would make sense if prop walk only occured when the the blade is
moving through a horizontally advancing medium (water under the boat).
That effect I'm sure is a contributing factor though. But it's 0 when
the prop is not advancing through the medium, i.e, when you first throw
the boat in reverse from a standstill, the stern kicks out before the
boat starts moving significantly backwards. In fact, if you're moving
forward slightly and kick it in reverse, the stern keeps moving sideways
all the way from the slight forward motion through reverse motion,
including when there's absolutely no horizontal advancing medium. So
there must be some other cause(s) of prop walk as well.

Steve

On Thu, 10 Jun 2004 05:07:43 GMT, (Steven
Shelikoff) wrote:

So
there must be some other cause(s) of prop walk as well.

==================================

Absolutely, because we all seem to agree that prop walk occurs even
with horizontal prop shafts.