We hauled out in Charleston, Oregon to do some regular maintenance and bottom paint but we have also been having an engine or propeller vibration issue since we did our rudder fairing work 2 years ago. At that time we had replaced the Cutless bearing. The Cutless bearing supports the propeller shaft where it passes through the hull at the aft end of the keel.
One of the first things we noticed when the boat was hauled out this time was excessive play in the prop shaft. After pulling the propeller and shaft it was obvious that the Cutless bearing had overheated and melted (the bearing is actually rubber). This probably happened immediately after it was replaced two years ago. So I ordered a new bearing, but really needed to figure out why it failed so the new one wouldn’t.
We talked to the local boatyard people and they were surprised that we have no water supply going to the bearing. Apparently this is standard practice on faster power boats. I also called PYI inc., the distributor of our propeller and shaft seal. We have an older version of their shaft seal (PSS) and the newer ones come with a hose connection that can be used as a water supply or a vent. They recommend using it as vent for a sailboat. I ordered the new shaft seal part also.
The new bearing arrived and I set about installing it. I removed the stern tube (this is the housing that the bearing is in). I had been wanting to remove it anyways to improve alignment with the engine. After removing the old bearing, I think I discovered the real cause of the bearing failure. There is a shoulder half way down the tube that the bearing seats against. What I found was that there is a large radius at the shoulder. When I installed the old bearing I drove it too far into that radius which compressed that end of the bearing. That would have made it too tight and restricted the water flow through the grooves that are in the surface of the bearing.
So I am hopeful that with correct installation of the new bearing and addition of the vent line to the shaft seal, the new bearing will last many years…