Propeller Drag

There’s no consensus on whether or not to lock it
Does a sailboat propeller cause more drag under sail when it’s fixed or when it’s allowed to rotate? The answer seems to be that there’s so little difference, nobody can really tell.Dave Gerr, a respected New York naval architect and author, asserts: “The simple answer is that a propeller creates less drag when free to rotate.” But, he adds, if you can hide a two-bladed propeller from the flow of water by locking it vertically behind a skeg or keel, it produces less drag than when it’s rotating freely.On the other hand, Francis Kinney, an equally well-respected naval architect, maintained in Skene’s Elements of Yacht Design that “the shaft should be locked so that the propeller cannot revolve. It has been found that a revolving propeller causes more drag . . . ”Eric Hiscock, a vastly experienced British sailor and author, wrote: “Experiments made by P. Newall Petticrow Ltd. have shown that a two- or three-bladed propeller offers less drag when it is locked than when it is free to spin, and that the drag of a spinning propeller is greatest at about 100 rpm.”Some sailors don’t have a choice in this matter; on certain boats, the propeller must be locked under sail because the transmissions will not be lubricated when the engine is not running.On ocean passages, most sailors lock the shaft for the simple reason that the noise of the racing screw is unacceptable.See also other entries under Propeller.