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

Museum ships do have to enter drydock or they’ll cease to float. When they’re converted to museum ships, the owner may decide to perform modifications that make the seal more permanent (removing/cutting the shafts and blocking off the port, or at least removing propellers to reduce radial load on the seal).

Most boats I’m familiar with use either a modern seal package that has several different seals and bearings in a single assembly, or they use packing, which is essentially a fancy rope impregnated with something like wax.

Very large ships would have a highly engineered seal, but might still suffer from a certain amount of normal leakage.