I'm reading from the Jan 1,1995 article "MIT Propeller Test - Part 2." The
Michigan Wheel 3-blade had about 70 pounds drag at 8 knots. This is a huge
amount of drag, costing maybe 10% of boat speed. The earlier article (Oct 1,
'93) had the same numbers plus a discussion on how much speed this would cost.
They predicted 1/3 of a knot improvement, averaged over a wide variety of
conditions, for a 25 foot boat when removing a 3 blade prop.
I'd agree with some of your conclusions, especially that a folding prop is
perhaps not useful for the OP's Westsail. Since a 2-blade fixed can be lined up
in the aperture to minimize drag, there's little reason to sacrifice reverse
capability with a folder. I can't imagine trying to "crash stop" a Westsail
with a poor performing prop.
However, this is not true for a lot of boats. Many fin keel boats have the prop
too far from the keel to benefit from lining it up. Boats with Saildrives don't
have that option. Light weight boats that rely on low drag would be affected
worse by a high drag prop. And catamarans, with two props would have double the
drag with fixed props.
"JAXAshby" wrote in message
...
jeff, are you sure of that 25 to 35 pound figure at 7 knots? I recall 170# at
5 knots.
35# at 7 knots is only about 3/4 hp. not worth thinking about.
If you insist on calling the Autoprop "feathering" then you have to admit its
a
pretty poor one, having 5 to 10 times the drag of other feathering props.
For
example, in the MIT/Practical Sailor test, at about 7 knots the Autoprop had
10
pounds of drag, while the 2 and 3 blade Maxprop feathering props had about 1
and
2 pounds respectively. The folding props were so low they weren't shown. 10
pounds of drag is pretty good, compared to the 25 to 35 pounds for many of
the
props in the test, but it isn't the same as feathering. The Autoprop has
some
interesting properties, like very good performance in reverse, if you rev it
up.
"Jim Richardson" wrote in message
...
On 04 Sep 2004 13:08:18 GMT,
JAXAshby wrote:
Then why did you post a definition of feathering, which fit the
autoprop?
it does not fit. not even close. and if you had not blown $2,200 on a
prop
hoping against hope you could make your boat *sail* faster you would know
the
difference.
Did the dealer tell you you could pass Island Packets and Westsail 32 if
you
bought an auto-prop?
I didn't buy one JAXAshby. I simply wanted to know what you meant by
calling it a non-feathering prop. Alas, I should have known better than
to expect rational discourse from you.
--
Jim Richardson http://www.eskimo.com/~warlock
'Windows' really does make a fine swear word, representing all that's
taboo and awful - just like '****', '****', etc."
-- Mark Hughes, sdm