[paulk]

This question comes up often enough to generate considerable discussion on occasion, with various anecdotes, but the upshot is what you know applies in the air also applies in the water. The trick is to mark your propshaft when the blades (of a two -bladed prop) are vertical and thus not projecting beyond the "shadow" of the keel. Then you engage the clutch when the mark shows, and you''re done until you need the engine.