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

In the old days it was a stuffing box. I worked on pulley-driven pumps with gland seals, the same principle; stuffing box HAD to drip or the gland packing would burn out. There was a network of drainage pipes in the boiler rooms to funnel the drips into a drain.

On ships, if the gland packing was overtightened, it could glow red. I’d assume you’d just undo the nuts and put more packing into it in service. The QM is stationary, you could tighten the gland packing up as tight as you like. Does it still have propellers?

Pumps have now changed to carbon/graphite seals, they don’t need to leak. I’d assume ships use the same technology.