How they make propeller shafts on large vessels like ocean liners or aircraft carriers waterproof considering the intense water and mechanical pressures that come into play?

Question

It seems like a grommet-type seal would fail in no time. Also, looking at an image of one of the propellers for the Queen Mary, it hit me that this is decades old, and would have to go to dry dock to be serviced, and there is no way they are doing that so… How is that even possible? I’d figure dry rot would set in somewhere along the way.

In: Engineering

Answer 1

Former submarine mechanic here.

They aren’t waterproof. 6 gallons a minute is an acceptable leak rate for in service boats. The main seal was a very smooth but brittle carbon ring that perfectly fit the shaft in 2 pieces. Water is pumped into the seal ring to counteract the ocean pressure. In event of a catastrophic leak, there is an inflatable rubber boot outboard of the seal that gets pumped with water after the shaft is stopped.