Folding vs. Feathering Prop?
I have a 1984 Hunter 34. 24 HP yanmar 3-cyl. Right now making 5 1/2 kts. cruising speed, looking to pick up a little more thrust to power through a head wind.
Does anybody have any experiance with either a folding or feathering prop, looking for advice. Folding vs. feathering, two vs. three bladed. Is it worth the money?
I use a 15 inch 3 blade maxprop on my Beneteau 36CC. It works well, particularly in reverse (less prop walk). Good customer support to get it set up properly for the boat and engine. It is a little pricey. You will pick up 1/2 knot or so under sail when it feathers.
You have asked a complex questions, to which there are varying answers. If you do a search on this website, you will find several posts comparing feathering and folding props, and also some pointers to websites where they compared feathering, folding, maxprop, 2 blade and 3 blade props for resistance while sailing and for thrust in forward and reverse while motoring.
As I recall, the best were the folding, followed by feathering, then 2 blade, then 3 blade for least resistance while sailing, and I think in reverse order for motor thrust.
Even amongst the generic "types" there are differences.
Folders: include "geared" and non geared types. The gear types guarantee that both blades open (and fold) together. Non geared folders can (and do) occassionally open one side only, creating a lot of vibration and wobble that could, if allowed to, possibly damage shaft or struts. Drag wise they are comparable.
Feathering props include Max, Autoprop, Kiwi prop and others. They vary in price, with Max generally thought of as tops in both categories (price and quality) Figure $3-4K for a 3 blade for your boat. These are tops in performance under power and in reverse over folders and do not have the "1/2 open" problems of some folders. The nice thing about Max props is the blades rotate in reverse mode so that the blade itself is always acting in a forward direction, increasing efficiency quite a bit.
A midway alternative to either if these, with greatly reduced drag over a conventional Michigan wheel, is a Campbell Sailor prop. 2 or 3 blades available, we had good success with a 3 blade one on a 40 footer, replacing a worn out floppy folder. That prop cost $700, looking good against the prices of the others. If you google Campbell Sailor you'll get a link to a supplier.
Feathering and folding props
I have a 3GM30F Yanmar on a C+C36. I was using a folding 17"x10" Martec that is a good match to the engine. MIT tests show it is very effiicient in forward. A fixed pitch prop can have max efficiency at one speed. It is nice in that it doesn't have to be locked to stop auto rotation. Just put it in gear to stop the rotation and then into neutral.
I switched to a 16.3" 3B Autoprop to get smoother operation and more reverse thrust. The MIT tests showed this auto pitching prop got more efficiency at any speed. This prop was not a good match to the engine, i.e. 6 K @ 2100 rpm rather than 6K @ 2500 rpm for the Martec. It was not smoother. It auto rotated unless I put the engine in reverse. Then it jams there with the water pressure and the engine had to be started in reverse. It did provide good reverse. The final blow was a blade fell off and it will cost almost $2K to repair.
A feathering prop will not be as efficient. It should not auto rotate. Getting the pitch right is VERY DIFFICULT. Feathering props usually have adjustable pitch in both forward and reverse. I recommend 17" 2B or 16"3B for your engine if it is a 3GM Yanmar.
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