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10% of max boat speed = 1/3 knot??
That one heap slow mutha boat. 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 |
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