Stern bearings question

[GuestfromEU]

Yes yes, of course the seals would not actually have a lifespan of so many years. Typically, I have seen them changed out at each special survey, 5 years duration in service. The bearing surfaces will have a much longer lifespan.

I forget the Great Lakes has a bit of a different circumstances regarding the abuse the vessels see, along with fishing nets, foreign objects, etc.

I have not personally worked with the Thordon water-lubricated bearings, but they do seem to be popular in some circles. Fortunately, my 20+ years at sea has not experienced losing a shaft seal, but I have worked some older, smaller vessels that had water-lubricated lignum vitae bearings...quite an experience. I have seen plant/vegetable-based oils used in shaft seals and bearing systems, and deck hydraulics. It is not so big of a concern if those oils enter the sea.

The name of the game today is build it quick, build it cheap. Spending 5+ years as a construction team manager in South Korea (DSME) has been an eye opener. Those new Algoma and CSL ships will be done in 15-20 years, max. But, why build them with "extras" when the technology will change so much in just five years time? Save your money, build it cheap, and 10 years from now it can be replaced with something that is more efficient, up to date, and so on.

[GLEngineer]

For clarification, water lubricated stern tube bearings have packing (usage of this system was uncommon even 40 years ago). In this case, you would re-pack the seal...the bearing is likely a bronze alloy and is replaced in dry dock when worn.

Oil lubricated, oil sealed stern tube bearings are the most common system in use on merchant ships. No seawater is admitted into the ship. The stern tube bearing is lubricated by circulating oil under pressure, and the inner and outer seals are maintained by natural head pressure (a tank inside the ship is positioned at a higher level than the loaded waterline).

I have been on board some vessels with an inflatable rubber seal which will allow the (oil) seals to be replaced from inside the hull, no diver or dry dock required. This is old technology though as new seals rarely leak and bearings will last the expected life of the vessel (25-30 years)

The water cooled/lubricated sterntube bearing has had a resurgence since the introduction of the Thordon Sterntube Bearing. http://thordonbearings.com
Many ship owners are replacing their oil filled bearing with the Thordon Bearings and new internal water shaft seals so to reduce the risk of pollution and the now very hefty fines for pollution caused by a leaking seal. Especially in sensitive waterways such as the Great Lakes
The sterntune Oil Seals especially the outer seals rarely last 20 to 30 years as they are easily damaged by fishing lines and other debris getting between the shaft and the seals or normal wear and are replaced every time the tailshaft is pulled for inspection every 5 or 10 years depending on Class rules and type of service.

[A Guest]

Deckstir , Thank you for the answer an the pictures that you recorded for history . The AKA had a very strange life after her diesel conversion an years tied up.

[deckstir]

According to Scotlund Stivers, who was the Atkinson's owner while she was at Detour, prior to the scrapping, there was a tailshaft seal leak. He stated that he paid someone to replace the seal with a new "okum rope" seal but instead they injected grease into the leak to stop it. Following the winter, the grease expanded and washed out making the small leak worse and that's why the shaft alley and KaMeWa room flooded and she settled at the stern.
This is what was told to me by Stivers when he let me tour the Atkinson at the Interlake coal dock in Detour, 6-26-07.
She had been pumped out when I was onboard and was routinely kept pumped out until she was towed out to the scrapper.

[Pete in Holland MI]

Not sure why the Atkinson took on water. Shaft packings normally won't fail sitting at the dock. They wear as the shaft is turning. Could have been several things (broken pipe, frozen sea cock, port hole left open, accumulated rain water, etc) that failed.

Pete

[A Guest]

Is this the final failure that caused the late Arthur K. Atkinson to fill will water an settle to the bottom while in storage at Detour ? Thanks !

[CRJ]

The stern tube seal is often a sorce of trouble for ships on the Great Lakes. The seal is made up of a number of rubber rings that keep sea water out of the ship. The area between the rings contains oil that acts to lubricant the system and to provide the pressure against the sea. Lakes vessels operate very close to the bottom and kick up sand and silt. This sometimes damages the seal and causes it to leak oil out. When this happens the secondary seal is activated until repairs are made. When you see a ship docked for "repairs" with the propeller hub out of the water, it's often the stern seal that's being repaired.

[GuestfromEU]

For clarification, water lubricated stern tube bearings have packing (usage of this system was uncommon even 40 years ago). In this case, you would re-pack the seal...the bearing is likely a bronze alloy and is replaced in dry dock when worn.

Oil lubricated, oil sealed stern tube bearings are the most common system in use on merchant ships. No seawater is admitted into the ship. The stern tube bearing is lubricated by circulating oil under pressure, and the inner and outer seals are maintained by natural head pressure (a tank inside the ship is positioned at a higher level than the loaded waterline).

I have been on board some vessels with an inflatable rubber seal which will allow the (oil) seals to be replaced from inside the hull, no diver or dry dock required. This is old technology though as new seals rarely leak and bearings will last the expected life of the vessel (25-30 years)

[Pete in Holland MI]

I think what is being referenced is the packing around the shaft. As the shaft turns, the packing is worn & consumed, requiring occasional adjustment & tightening. Eventually most of the packing is worn out or gone, and must be replenished. In order to do that all the old packing is normally removed and new stuff put in. This though, is the only thing holding back the water outside. Provisions to temporarily stop the water from outside with a diver, or waiting till the boat is in drydock, are needed.

[Guest]

When working on the stern bearings, is the proper term "refilling" or "repacking" the bearings? Thanks for any replies.