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

Water cooled ceramic seals. Cotton ring seals are also used on some large ships, mostly much older. Ceramic is preferred because they don’t leak into the ship bilge. Cotton or other fibre seals require a drop of water every second per inch if shaft diameter, so for a 24” shaft it’s a lot of water that has to be processed through the oily water separator. Plus they are very time intensive to keep adjusted and lived properly.