Prop Drag :folder vs Max

[Silmaril]

While not employing sophisticated test gear, back in the early eighties, I was working with the owners of a Peterson 34 to eek out every last 1/10th of a knot. Over a weekend, we tried 3 different props. with her 2 cyl. Yanmar diesel. We went with the then new Gori, a Martek, and a 2 blade "Sailor" for sails. We logged as much info as we could. Swapping the wheels twice each. Pain in the arse, actually. When all was said and done, we settled on the Martek. It looked to be marginally faster under sail. Could have been atributed to diferent wind and wave conditions between the time it took to change the wheel and get back sailing. Stricktly seat of the pants, back to back stuff.

That all being said, "Your results may vary" The hull shape/form and factors such as where the prop is positioned and how much of it is "exposed" to undisturbed flow etc. comes into effect. The effects of a different prop would be more noticable on a highly refined racing hull design, then a more cruising oriented boat.

But when you are worrying about that extra little bit of speed under sail, it''s rarely the prop that will make a difference. Proper sailing skills, and a clean bottom go far more towards overall speed than the prop will ever make.

Caveats: The Martek may be slower under sail in light wind if you fail to line up and then lock your shaft so that the blade hinge is vertical. If you don''t, gravity will take over and one of the blades will fall open. Noticable? Maybe in a lab, but winning takes covering every little detail. The feathering props have some additional drag if the prop shaft is not completely horizontal. Many boats have the shaft angled down. The feathering props are designed so that on a completely horizontal shaft, the flow over them is minimized. But as the shaft angle increases, the "ideal" flow over them is changed to a more angled flow. Causing a bit more turbulence. Measuable in the lab, sure. Can you feel it on the water? Probably not.

Basically, go with a properly fitted wheel, of whatever design you prefer. Keep your bottom clean, hit the starts on time, always choose the right sail, always go the the correct side of the windward leg, never blow a gybe, and whaterver prop you use wont really matter.

[JDAM]

Silmaril

Thanks again for the input. While the boat is quite old, 32 yrs to be exact, the bottom is polished VC offshore, the inventory is primarily Doyle/ North Kevlar, and the rudder, an eliptical Gary Mull re-design. The last outing in the fall produced a win over a Quest 30 rating 90 and J29 in about 15 true, first prize being 30 % off the yard bill. I know about the importance of the details you noted, and after going to all the trouble I dont want to add a prop that has significantly more drag.

The knowledge here about this is more than my own.

[Silmaril]

Well, if you have gone that far in race prep all ready, by all means, go with the Martek.

You can also do a little trick we used in the past as well. Once at the starting area and you are done with your motor, have a crew jump over with a light rubber band, something that fits snugly around the folded blades. Not too big a rubber band, you want it to come off/break-free when you put it in gear after the race. Not too small either, you want something that will stay on during a blast reach as well. This will keep the blades folded, and keep them from flapping in the chop that sometimes accompanies light or no breeze.

Every little bit helps.