jackieschmidt
Gold $$ Contributor
Two weeks ago, I was called out to one of our Shipyard Customers to look at a large Push Boat, the MV King.
This vessel is only 13 months old. We did all of the Machine Shop work when it was built at San Jac Marine.
Some information. Large vessels use water lubricated bearings. For years the most popular have a brass shell with a hard rubber inside vulcanized into the shell that the shaft journal runs in.
This type of bearing has served the industry well for decades.
For the past couple of years, various customers have had problems with the rubber coming loose in the shell and then coming out. This causes the shaft to drop to the brass shell. Needless to say, this is a catastrophe.
This happened to The king. The problem, they kept running the boat. The crew complained about noise and vibration, but someone high up decided to keep the boat in service.
it finally got so bad they had to get the boat on dry dock.
As you can see by the pictures, the shaft wore all the way through the remaining brass shell and almost all the way through the steel strut housing.
I determined we would have to get a new strut housing, have the shipyard install it, then we would align bore the new housing true with the stern tube.
The shaft was another matter. This is a 8” diameter 36 ft long shaft with 8.500 diameter journals.We got it to the shop, did a die penetrant check for cracks, and found a severe fracture just outside the stern tube bearing journal, where it exits the hull.
The shaft was dead on arrival.
So we had to machine a new shaft as well.
Instead of going back with the rubber/brass bearing, they decided to go with Thordon “Rivertough” shaft bearings. This is a total composite bearing that has proved to be superior to just about anything. The drawback is you have to use shrink on liners on the shaft that are coated with Nickel/Crome/Boron, and then ground to finish. This coating is around 60 RC hardness. We bore the liners to shrink on the shaft in way of the journal with a .002 interference fit.
It is a shame they let this new vessel get to this point. If they would have shut it down the minute it started making noise, they could have avoided most of this repair.
Here are some pictures I took of most of the job.
This vessel is only 13 months old. We did all of the Machine Shop work when it was built at San Jac Marine.
Some information. Large vessels use water lubricated bearings. For years the most popular have a brass shell with a hard rubber inside vulcanized into the shell that the shaft journal runs in.
This type of bearing has served the industry well for decades.
For the past couple of years, various customers have had problems with the rubber coming loose in the shell and then coming out. This causes the shaft to drop to the brass shell. Needless to say, this is a catastrophe.
This happened to The king. The problem, they kept running the boat. The crew complained about noise and vibration, but someone high up decided to keep the boat in service.
it finally got so bad they had to get the boat on dry dock.
As you can see by the pictures, the shaft wore all the way through the remaining brass shell and almost all the way through the steel strut housing.
I determined we would have to get a new strut housing, have the shipyard install it, then we would align bore the new housing true with the stern tube.
The shaft was another matter. This is a 8” diameter 36 ft long shaft with 8.500 diameter journals.We got it to the shop, did a die penetrant check for cracks, and found a severe fracture just outside the stern tube bearing journal, where it exits the hull.
The shaft was dead on arrival.
So we had to machine a new shaft as well.
Instead of going back with the rubber/brass bearing, they decided to go with Thordon “Rivertough” shaft bearings. This is a total composite bearing that has proved to be superior to just about anything. The drawback is you have to use shrink on liners on the shaft that are coated with Nickel/Crome/Boron, and then ground to finish. This coating is around 60 RC hardness. We bore the liners to shrink on the shaft in way of the journal with a .002 interference fit.
It is a shame they let this new vessel get to this point. If they would have shut it down the minute it started making noise, they could have avoided most of this repair.
Here are some pictures I took of most of the job.
Last edited:
