charles_reed
Active member
Agree, the thread is long on conviction but short on facts.Not quite what you have asked but I have tried to create what would be a catastrophic failure with a mechanical shaft seal and failed.
All our boats have always been specified with lip seal based shaft seals. On one of the early boats (1-1/2 inch shaft from memory) the assembly was on the propeller side a bronze water/grease lubricated bearing and on the engine side of that a single lip seal held in place by "lantern" ring.
In an experimental mood I one day took the "lantern" ring and the lip seal out while the boat was still in the water. With NO SEAL AT ALL no water came into the boat the grease and fit of the bearing stopped it. I then started the engine and put it in gear and at most I could just get an easily controllable dribble of water coming into the boat much of which may have just been the water injection from the engine raw water pump. Furthermore it was obvious that if one took the seal out and cut it from the shaft one could replace it with a twist or so of conventional packing - I quizzed the manufacturer on this and they confirmed that they too had that in mind as a possibility when they designed the seal.
I have seen a number of differing lip seal based shaft seals in the market, including the oil bath ones as well, that are incapable of failing catastrophically and I would suggest that people should extend themeselves and go looking for them instead of following the forum dribble about PSS and Volvo ones as if they were all that existed. Perhaps the original question should have been aimed at a specific mechanical seal type (if one was interested in a specific type) or else asked what seals are incapable of catastrophic failure. The latter would be more informative - and I have answered that question already.
Halyard withdrew their lip seal a long time ago. I had one of those and a Bukh seal, both leaked, either oil or water in time.
The Deep Sea seal has a questionable reputation amongst those in the marine stern-gear market.
The drawback of the packed seal is that it absorbs power - quite a lot on a small engine - and a number of FVs will complain of how they leak.
But glory be - most stern tubes are close enough to the surface that any leak is little more than a dribble.
One could always do a Pardey, and do away with prop-shafts entirely!!