I think I may have just become aware of an idiosyncrasy of the Autoprop when under sail. My boat has the M25XPB universal engine with the Hurth HBW 50 transmission. The owner's manual says it's ok to leave the transmission in neutral, or to lock the shaft by shifting into reverse when sailing. In bold type it says, "Do not shift into forward gear". During the last two weeks (it's a fairly new boat) I've noticed that the prop shaft freewheels or spins in reverse gear almost as well as it does in neutral. In looking at the geometry of the Autoprop, I think its tendency to rotate when sailing is in the opposite direction of a fixed blade prop. Now I'm wondering if the instruction to lock the shaft by using reverse gear is opposite as well, and should I just lock by shifting into forward gear now. I don't know if the warning about sailing while in forward gear is just to prevent freewheeling while in any gear. The shaft always turns freely in one direction or the other depending on whether it's in forward or reverse gear, and is locked in the opposite direction. I'm hoping that someone with an Autoprop who has dealt with this, or has more knowledge than I, can clarify this issue. Otherwise I will contact the Autoprop and transmission companies.