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Size and pitch on a 3-blade MaxProp

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L

Lee Hound

Thank you all for your experience and help in finding the right feathering prop for my Sabre32. When I first asked the questions in June, many of you people helped me find the right answers. I have now a 3 blade feathering prop where was before a 2-blade fixed. I found out the following: 1. At the first seconds of motoring I recognized a lot less vibration, so the overall engine noise appeares to be much softer and lower. She's now humming like a turbine! ( Westerbeke are nicely balanced motors anyway) 2. Picking up rpm and speed, I didn't find substantial differences to the fixed 2-blade, specifically the maximum speeds appear to be the same. I didn't notice improvements in thrust, but that remains to be seen once I get into high swells and headwinds. Over all the engine rpm appear to be a little higher in the middle ranges, same in high ranges. So I wouldn't know why to change the pitch for now. 3. Revers: The BIG change! No prop walk whatsoever, nice pull, great stopping power. A breeze to manouver the boat backwards. 4. Sailing: Another positive surprise, but not as big a change as some people claim. I may have gained about .5 to .75 knots in light air, she might also point a little higher. (Simple mathematics) Since I had tuned the rig at the same time it's hard to say how much influence the prop has. But the combination of both certainly did the trick! Over all 1+ knot speed improvements in light to moderate air! Lee
 
T

Trevor - SailboatOwners.com

Thanks for the report

Hi Lee - Thanks for the report - sounds like you are MAXimizing (pardon the pun) the prop you bought. I have experienced similar results on boats that I've upgraded. The overall thrust difference between 3 blades and 2 difference will be noticed in a headwind with chop. You should have more torque and keep speed up. Enjoy sailing faster in light air! Best, Trevor
 
Jul 1, 1998
3,049
Hunter Legend 35 Poulsbo/Semiahmoo WA
Pointing in Light Air

Nice write-up! With regard to light air, though, there should be a noticeable improvement in tracking because there is less drag. This can be easily seen by sailing upwind against and astern of another boat in light air with the transmission in forward and then puting the transmission in reverse causing the prop to feather. The boat will immediately start to track lower due to the increased drag. Sounds like sailing enjoyment has just gone up another notch!
 
J

Jack

John do you mean?

that a feathered prop has more drag than an un-feathered prop? We have found that we point lower with the prop feathered because we are going faster due to LESS drag. This is because we move the apparent wind forward due to the increased speed. The big benefit of the prop is reverse thrust.
 
Jul 1, 1998
3,049
Hunter Legend 35 Poulsbo/Semiahmoo WA
Oops..... (reply to Jack)

Totally agree - Feathered prop has less drag than un-feathered prop (or fixed-blade prop). Can't believe I posted what I did! Had something else in between and deleted it then didn't re-read my post. Haste makes waste! Your analysis is correct. Actually a better description I could have used would be when following another boat with the shifter in forward and the feathering prop deployed like a fixed-blade then shifting to reverse causing the feathering prop to feather you can really see the boat track higher and feel it pick up speed. Starting with the prop in feathering mode and shifting to forward (what I wrote) may or may not cause a change in speed and pointing. It's possible if the blades are exactly aligned with the centerline they may require the engine to be turned on in order to deploy. You gotta love those low-drag props!
 
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