PCM Direct Drive. What is the collar on the drive shaft with allen set screws?

[Crab]

I have a '99 Pro Air Nautique with PCM Direct Drive. New to me so getting to know my boat. Upon opening the inspection cover behind the dog house, I noticed a solid steel doughnut that has two allen set screws that was right against the packing on the drive shaft. It was loose and slides up and down. There is very slight wear on the shaft where it has been free spinning against the packing jam nut. What is this collar and where does it go? Thanks.........Crab

[Yiger]

I have seen them used on some boats as a fail safe to keep the shaft from pulling out of the cutlass bearing if the shaft were to pull out of the transmission when in reverse (an uncommon but not unheard of issue). Not sure that is the case with your boat though- and it obviously wouldn't do much if it were loose!

[s_kelley2000]

Yiger is on the right track, it is a safety collar. If the shaft broke or came loose from the press fitting in the coupler then this safety collar is designed to keep the shaft from slipping all the way out of the boat. If the shaft breaks or slips out the prop could slam into the rudder causing the boat to turn violently. Your shaft and prop could also potentially slip all the way out and end up on the bottom of the lake and leave you with a 1" hole below below the water line since your stuffing box would now be empty. Sounds like your safety collar needs to be tightened up if it is spinning freely. It should be located pretty close to the packing jam nut (I wanna say an inch or two above) so that if there is a drive shaft failure it can only slide back a minimal distance and not hit the rudder.

[Crab]

Makes sense, thanks again. More questions to come..........