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Angle of prop shaft - theoretical question.
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
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