Thread: What is propeller windmilling?

It's a reasonable question. Many props have pretty sharp blade edges that can cause injury even when static due to human movement. Any prop rotation adds add'l slicing characteristic to any human contact.

And by all means, practice your recovery method every time (or every other time) you go out. Your approach could save a life. Have admiral and kids practice it too. Always come around with the bow into the current or wind (whichever is strongest) for a smooth stable approach.

Stopping the engine is safest but Bruce is absolutely correct about the need to have the engine running for the clutch to operate. Simply turing off the engine in gear will not necessarily stop the propeller.

Trying to educate myself a little more in my boat and safe boating, I was reading through some manuals and whatnot. In one section about retrieving an overboard person, it says to approach the victim slowly, then "when almost alongside, stop the engine in gear to prevent propeller "windmilling". What is propeller windmilling? and do you agree with cutting the engine in gear like that whether it is an emergency situation or not?

some props will still turn while in neutral if the engine is running or in a current even with the engine off. They are saying to turn off the engine and put it in gear to stop the prop spinning. Unfortunately many transmissions on larger straight drive boats require hydraulic pressure to lock the coupling, that pressure is unavailable with the engine off so the prop can spin regardless of gear selector position. Many outboards and I/Os...

quote: Originally posted by pdecat some props will still turn while in neutral if the engine is running or in a current even with the engine off. They are saying to turn off the engine and put it in gear to stop the prop spinning. Unfortunately many transmissions on larger straight drive boats require hydraulic pressure to lock the coupling, that pressure is unavailable with the engine off so the prop can spin regardless of gear selector...

Just for the sake of clarity, if a prop is windmilling, can it actually do damage to a person? Is there any force behind it? Could you theoretically stop it with your hand? If, as Sandy says, it is free-wheeling, is it really an issue? I'm not giving push back, I simply am curious how this works. Peter

Maybe not fast enough for cutting or slicing but the movement alone is a potential tangling or trapping situation. Also a big prop is also heavy so at very low rpm it's own inertia still packs a heavy slicing punch.

One of stopped props slit my leg open, when a boat wake tossed me overboard off the swim platform.