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Subject: [worldcruising] Folding and Feathering Props, Etc..
mark_melvin@XXX.XXX
Date: Thu Jan 25 2001 - 09:30:44 EST
Folding, feathering, or self pitching, all are improvements over
fixed props when sailing.
Traditionally, folding props are the ultimate in sailing
slipperiness, but suffer in motoring thrust, and tend to really
suffer in backing down / stopping operations. They're improving,
but end result is that if sailing speed at any cost is the goal,
a folding prop is great and relatively cheap but your motoring
will be a small bit less than your fixed prop, and you should
allow a bit more margin of safety when backing down or stopping.
The MaxProp (and other feathering props) was 99% as slippery as a
folding prop when sailing, but (MaxProp in particular)
significantly better than a folding prop for motoring. The
MaxProp is different from other feathering props in that the
blades totally reverse, making a huge difference in MaxProp's
stopping ability; it exceeds a fixed prop where other feathering
props are not much better than folding props when backing down /
stopping, and some feathering props are horrible at stopping a
boat.
Compared to the AutoProp self-pitching prop, the MaxProps are a
decent amount slipperier when sailing, and perhaps just a much
less powerful for motoring (factory claims that they're similar,
but we're talking about the independent study results here). The
fact is that the MaxProp is just about as good as a fixed prop
for motoring, but the amazing AutoProp is actually _better_ than
a fixed prop for motoring. There is a catch, however. Even with a
shaft brake, the when sailing AutoProp has a tendency for the
ears to start to "reverse deploy" themselves when sailing,
starting at about 4.5-5.5 knots depending on which analysis you
favor (discrepancy probably a due to different sized AutoProps
being used by different studies) and therefore slowing you down.
In the MIT studies the MaxProp had the BEST stopping and
reversing of all props (better than fixed, folding, or
self-pitching), due to the fact that the blades completely
reverse so that the lobes are properly oriented and when reversed
they have a fixed "stop" against which to bear, making them a
reverse-oriented fixed prop in the approximately 1/2 revolution
of the shaft it takes for the blades to reverse. Not all
feathering props do that, it is a feature of the MaxProp (which
also costs double what other feathering props cost)
I have no connection to any prop maker, except that I have a
MaxProp 3 blade on my boat.
Mark Melvin
OC 461 "devocean"
http://www.beneteau-owners.com volunteer webmaster
(if you've got a Beneteau, please visit _your_ website ;-)
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