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
We can also swap in a new seal while the ship is in the water!
Modern sealing arrangements have a air bladder we can fill that closes off the sea to seal passage. We then remove the old seal and push the spare seal down the shaft into place and secure it.
Drop the air pressure out of the bladder check for leaks and start up the engine again.
We normally carry one spare seal on the shaft and while there are split seal you can install we always prefer the single piece ones.
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.
Well, with small boats, you pack tight around the shaft with a special oiled rope that’s water repellant. It still leaks some (or, rather, if you pack it tightly enough to not leak at all, it will make enough friction to ignite the rope, so you deliberately leave it a bit loose and leaky), but it’s nothing a bilge pump can’t handle. I imagine there’s something similar going on when you scale it up
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