I started my search for a feathering prop in the assumption that it would reduce drag under sail, and maintained efficiency under power. After much research on the net and the phone, I am still not convinced about the second point. As it turns out, feathering props such as Maxprop, Autoprop and Autostream, in order to minimize drag under sail, have blades with constant pitch, that is they have flat blades. Autoprop has blade profiles with some curvature and adjusts its pitch to maintain an ideal angle of attack at varying RPM and boat speeds. However, it does not have twist on its blades. As far as I know, propellers need to have twist in their blades to accommodate the higher speed of the blade at increasing distance from the shaft. Has any body seen an airplane or water propeller without twits in the blades? In a flat blade, the pitch angle is the same close and far from the shaft, making the relative angle of attack of the water over the blade different than the orientation of the blade except in one point. This should result in a loss of efficiency under power although I don’t know how by how much. I realize that for sailing, a feathering blade with twist (if there was such a thing)would result in additional drag compared with a flat blade, but I feel it would still be a lot less than that of a fix prop. Does any body knows of a feathering, or folding, prop that has twist in the blades? I know that even airplanes with adjustable pitch props, such as turbo-jets, come with some twist in their blades.
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Tim Porter
Twistin' Blades
Jose, As a commercial pilot, I can tell you that you are right on with your analysis. To be precise, aircraft propellors (including jet engine turbine blades) actaully have LESS pitch as you get farther out on the blade. This is because the outer portions travel at higher "tip speeds" than the inner portion, so to maintain a constant angle-of-attack along the entire blade when traveling forward, it must have the twist. Now, as for your prop dilemma... I just bought a 2-blade Flex-O-Fold and it does have twist. They claim to be the highest efficiency folding prop on the market. I also looked at Gori props, which have the twist, but was more impressed with the Flex-O-Fold, even though it cost more than $100 extra than the Gori I could have used. My old original prop from Beneteau (1983 First 32) was a piece of junk. Constant blade angle, and very thick, inefficient blades. I can't wait to see how my new prop performs (which by the way spec'ed out at 2" less in diameter than the original!). Give Chuck Angle at call in Massachusetts, his # is on the Flex-O-Fold website at www.flexofold.dk under the U.S. distributor AMSales. Or you can email him at CANGLE@WELLSYACHTS.COM. The website also has a neat prop calculator that will tell you within minutes the proper prop for your boat. Tell Chuck that Tim Porter referred you. Good luck, and let me know what you decide. Tim Porter TKP62@aol.com
Jose, As a commercial pilot, I can tell you that you are right on with your analysis. To be precise, aircraft propellors (including jet engine turbine blades) actaully have LESS pitch as you get farther out on the blade. This is because the outer portions travel at higher "tip speeds" than the inner portion, so to maintain a constant angle-of-attack along the entire blade when traveling forward, it must have the twist. Now, as for your prop dilemma... I just bought a 2-blade Flex-O-Fold and it does have twist. They claim to be the highest efficiency folding prop on the market. I also looked at Gori props, which have the twist, but was more impressed with the Flex-O-Fold, even though it cost more than $100 extra than the Gori I could have used. My old original prop from Beneteau (1983 First 32) was a piece of junk. Constant blade angle, and very thick, inefficient blades. I can't wait to see how my new prop performs (which by the way spec'ed out at 2" less in diameter than the original!). Give Chuck Angle at call in Massachusetts, his # is on the Flex-O-Fold website at www.flexofold.dk under the U.S. distributor AMSales. Or you can email him at CANGLE@WELLSYACHTS.COM. The website also has a neat prop calculator that will tell you within minutes the proper prop for your boat. Tell Chuck that Tim Porter referred you. Good luck, and let me know what you decide. Tim Porter TKP62@aol.com
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Joe Barrett
Autostream by Martec
I have the Martec Autostream and it is more efficent than the 3 blade fixed prop that came with my boat.Excellent Reverse (got me out of a jam when I ran aground)and full speed in Forward. On the sailing front it added 1/2 kt to sailing speed! Best of all for me we installed in the water by a diver (though not recomended by Martec)
I have the Martec Autostream and it is more efficent than the 3 blade fixed prop that came with my boat.Excellent Reverse (got me out of a jam when I ran aground)and full speed in Forward. On the sailing front it added 1/2 kt to sailing speed! Best of all for me we installed in the water by a diver (though not recomended by Martec)
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Rich Lemieux
Flex-O-Fold
I just bought a 2-blade Flex-O-Fold as well. I liked the blade design on the Flex-O-Fold more then the Max. The price was nice too! I will be installing it this weekend. Good Luck
I just bought a 2-blade Flex-O-Fold as well. I liked the blade design on the Flex-O-Fold more then the Max. The price was nice too! I will be installing it this weekend. Good Luck
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Tim Porter
Flex-O-Fold
Rich, Please email me with some details of your boat, and I'd be curious to know how your new Flex-O-Fold performs compared to your original prop. I'm not launching til May 1st and am anxious to see how my new investment performs! Thanks, Tim Porter TKP62@aol.com
Rich, Please email me with some details of your boat, and I'd be curious to know how your new Flex-O-Fold performs compared to your original prop. I'm not launching til May 1st and am anxious to see how my new investment performs! Thanks, Tim Porter TKP62@aol.com
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Jose Venegas
I am sold on the Flex-O-Fold
Thanks for the tip, Tim. I liked what I saw in the Flex-O-Fold web page: efficient blade shape and minimal drag. I don’t know how the sellers of flat blade props can claim better efficiency that fixed props with twist’n blades. I am still not certain on the advantage of a 3 blade over the 3 blade Flex-O-Fold. Is it mainly smoother operation?
Thanks for the tip, Tim. I liked what I saw in the Flex-O-Fold web page: efficient blade shape and minimal drag. I don’t know how the sellers of flat blade props can claim better efficiency that fixed props with twist’n blades. I am still not certain on the advantage of a 3 blade over the 3 blade Flex-O-Fold. Is it mainly smoother operation?
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Don Alexander
Feathering Constant Blade Angle Props
Hi Jose, I fitted a feathering prop last year and it too has no wash out on the blades. On looking into the situation I realised that the outer area of the blades, near to the tips, does most of the work. They travel through more water, are moving faster and there is a square law at work. This leads to the conclusion that the area closer to the hub is much less important than one might at first think. Set the blade angle so that the correct pitch is achieved at about 85% of the diameter. My 3 blader feathering prop is a huge success and it far outperforms the fixed two blader which came on my 376. You will notice the folding lobby (and the advertisers) say nothing about your brakes or reverse performance. I once had a boat with a folder and, unless I let it stop before going into reverse, it used to just make froth out the back and still continue going ahead. Having experienced the feathering type no way would I go back to a folder. Of course feathering props are considerably more expensive - yet they sell plenty Regards,
Hi Jose, I fitted a feathering prop last year and it too has no wash out on the blades. On looking into the situation I realised that the outer area of the blades, near to the tips, does most of the work. They travel through more water, are moving faster and there is a square law at work. This leads to the conclusion that the area closer to the hub is much less important than one might at first think. Set the blade angle so that the correct pitch is achieved at about 85% of the diameter. My 3 blader feathering prop is a huge success and it far outperforms the fixed two blader which came on my 376. You will notice the folding lobby (and the advertisers) say nothing about your brakes or reverse performance. I once had a boat with a folder and, unless I let it stop before going into reverse, it used to just make froth out the back and still continue going ahead. Having experienced the feathering type no way would I go back to a folder. Of course feathering props are considerably more expensive - yet they sell plenty Regards,
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Tom
Feathering prop with Twist....Autoprop
You ask any body knows of a feathering, or folding, prop that has twist in the blades?....Yes aqnd you were alluding to it . The Autoprop actually has quite a bit of twist in the blades and much more at the hub. Have you seen one up close?....If you did you would notice the HUGE difference in blade compared to the other feathering props.. And yes exactly as you mentioned a feathering blade with twist like the Autoprop would result in a little additional drag compared with a flat blade feathering but it is almost negligble except for the slowest speeds and unless you were a pure racer you wouldn't notice. The props are a bit pricey though. Go to the website below to get info/pictures and a video clips
You ask any body knows of a feathering, or folding, prop that has twist in the blades?....Yes aqnd you were alluding to it . The Autoprop actually has quite a bit of twist in the blades and much more at the hub. Have you seen one up close?....If you did you would notice the HUGE difference in blade compared to the other feathering props.. And yes exactly as you mentioned a feathering blade with twist like the Autoprop would result in a little additional drag compared with a flat blade feathering but it is almost negligble except for the slowest speeds and unless you were a pure racer you wouldn't notice. The props are a bit pricey though. Go to the website below to get info/pictures and a video clips
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