"Driving home I thought about my coupling and went back the next day and sure enough the bolts had backed out. "
Sounds resonable, could you please expand and describe location of the coupling. The shaft is turining, but I can only see it turn inside the lazarette.
Thank you kindly,
In the hope that this helps you, here is a pic of my propeller shaft, and coupling.
To the left is the transmission, and to the right is the PSS Shaft seal (that I installed in the spring). If you look closely at the coupling you can see that I had not yet run siezing wire through the hole in the set screws. You can also see the end of the woodruff key sticking out of the coupling along the shaft.
I actually ran the engine for about 15 min without the siezing wire, and the screws backed out!
Fortunately, I found the set screws, and the coupling remained mated to the prop shaft by the brass woodruff key. There is another brass woodruff key connecting the prop to the shaft.
BTW the key is brass so that it can shear if the propeller stops. In theory, the keys should protect the shaft, and the prop, and the transmission, from damage.