Replacing a shaft seal

Will Renlinson replaces a shaft seal on his Jersey 36 motorboat before aligning the engine with the stern tube

- Stu Davis

Every marine engineer we have talked to has said that you need to realign your engine with the stern tube when the boat goes back in the water after a period on the hard, but how do you do this when your boat has a dripless seal?

It is possible to drop the shaft back just aft of the thrust bearing to have enough room to align the engine gear box to the shaft at the thrust bearing. Alas, with a dripless seal, you also need to align the engine with the stern tube so that the dripless seal will not leak. You cannot do this once the stern tube is covered with either a bellows or the hose of the lip seal type of gland.

The problem

We had a Vetus lip seal which was originally installed at the factory with a lazy loop water feed from a skin valve. Seaweed blocked the inlet while entering Harwich, causing the lip seal to burn out and water ingress.

We replaced it with a PSS (Proprietary Shaft Seal) seal, as it contains no rubber to burn out and is kept lubricated by taking engine cooling water once the engine is finished with it. We also installed a secondary inlet and weed filter for the main engine salt water cooling system, so we can switch between the two if a blockage occurs.

Due to the engine movement forward and aft on our shaft drive engine, we had to install the upgraded silicone PSS seal and over-compress the bellows to gain a seal. This was recommended by the PSS technical team, but was not ideal as it was very difficult to 'burp' the seal when needed, but it did work for three years.

This year, on a trip to London, we noticed a black carbon line coming from the stern gland, though no water ingress. It was not until we were able to get the boat out of the water that we found out what had been happening.