Join Date: Feb 2007
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Re: Propeller Drag - Challenging my intuition
I sail a Bristol 24 with a YSE8 diesel and a 2 blade prop. I put the transmission in neutral when sailing, but the prop rarely spins unless I'm doing hull speed. I have the propshaft marked so I can tell when the prop is vertical. The prop normally aligns itself vertically behind the keel at sailing speed less than 5 knots. However; when going fast enough that the prop spins, I have on several occasions, found the sailing speed to be less than it is when the prop is locked vertically behind the keel cut-out. I've seen from .1 to .5 knots difference immediately when the prop is stopped from spinning and positioned vertically. It's not much, but it's always slightly faster when stopped.
I can see where a boat with an exposed prop would have more drag when the prop is locked, rather than spinning, but for a full keel boat with a 2 blade prop, I don't see an advantage for letting the prop spin.
Privateer 26 Schooner