Irwin you are correct
about " puting a hose clamp on your prop shaft just above the ss disk, if the set screws which hold the disk fail the hose clamp stops the disk from moving forward"....I just wouldn't do it 1/4" up, I would have it touching....I don't want that stainless Steel donut moving at all!!I had the PSS on my old boat and it was great!!....I highly recommend it ...BUT !!....after 7 years then set screws on that stainless Steel donut must have loosened (or the bronze shaft wore?)..and that donut "shimmied" up the shaft while running one day, allowing water to start coming in the boat!!While I was motoring across Long Island Sound...my girlfreind went down below for a minute and yelled up...."Honey is there supposed to be water coming out over the lip of the engine compartment?" Yikes... HORROR! I flicked on the bilge pump and it took care of the incoming water..But It took a *while* for me to figure out that it wasn't any of the thru hulls , but rather where the shaft seal was.....(not very good access to that on my old boat....I had to be a contortionist)........But long story short....I slid that "donut" back down the shaft compressing the "bellows", tightened them back down and everything was better..........So I believe Irwins suggestion is mandatory.........Would I use the PSS again?....yes...no problem....Do I have it on my new '99 Cat 36?.....No...(because of the installation hassle)....What I did was just replace the existing stuffing box flax with a new high tech material called GFO® fiber dripless packing.....it works great....no drips this 1st year!!....and it costs under $20 !!Check out the link below