prop-factor

Thanks Peter and Bob. Interesting. I might go back to my fixed two-
blade, or ask Max-Prop to trade my three-blade for a folding two-
blade. The boat tracked true with the two-blade, and I don’t like the
constant pressure I need to apply to the tiller. I think, from your
comments, that the bigger bite from the three-blade is what is
causing the problem…

Again, thanks for steering me, and my boat, in the right direction…

Yes, its the bigger bite from the 3 blade. The shaft that turns your propeller is at a slight downward angle; so as you move thru the water (water going aft past the prop) the 'downward' traveling blade takes a bigger bite (the angle between the blade and the horizontal_______ water) than the 'upward' moving blade.

Therefore…the larger bite blade tends to move the boat in a slight
turn.

You can see this easier if you draw a cross section of two blades.
(draw a large letter
“X”  ) then rotate the drawing counter clockwise. Notice one blade has
a much greater angle (compared to a horizontal line_________) than the
other?   More thrust on the
downward blade because it has a much greater bite.

There you go…

Bob

joliebrise2003 wrote:

Thanks Peter and Bob. Interesting. I might go back to my fixed two- blade, or ask Max-Prop to trade my three-blade for a folding two- blade. The boat tracked true with the two-blade, and I don't like the constant pressure I need to apply to the tiller. I think, from your comments, that the bigger bite from the three-blade is what is causing the problem...

Again, thanks for steering me, and my boat, in the right direction…

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Granted that the three-blade Max-Prop with it’s greater thrust may pull to
stbd (and to port in reverse) somewhat more than a two blade folding prop,
but my experience has been that it is hard to beat a properly set-up
Max-Prop for thrust and maneuverability in tight quarters. As for the
2-blade MaxProp I know nothing, but I expect the three-blade would have more
oomph powering into a head sea. I do recall that a friend’s Tarten 10 with
folding Martec provided some exciting docking moments, particularly when
going into reverse.

My experience with Itchen has been similar to that with a Victoria 34 w/
3-blade MaxProp that I used to drive a lot. One can back & fill into a very
tight marina slip with much more control than with any other prop I’m
familiar with. True, on a long passage under power she’ll make big clockwise
circles unless one actively steers – or has a tiller pilot (my preference).
I guess the choice depends on how she’ll be used most of the time. Just my
$0.02!

Scott
S/V Itchen