The final vessel in a series of five ship-assist tugs has been successfully converted to Thordon’s “RiverTough” tailshaft bearings and TG100 shaft seals and has returned to work on the Mississippi River.
These five tugs are considered to be the first ship-assist tugs operating in the lower Mississippi fitted with both RiverTough bearings and TG100 seals.
The New-Orleans-based tug operator converted its first vessel, a 117-foot (35-metre), 4,200hp twin-screw ship-assist tug, in 2015 to reduce the operating and maintenance costs associated with traditional rubber tailshaft bearings and clad welded journals.
According to Thordon Bearings’ Sales Manager, Jim Bright, who was involved in all five retrofits, the owner specified the solution because it was tired of unbudgeted costs following frequent premature bearing and shaft wear.
“Their previous arrangements of rubber bearings had to be replaced every two years or so and the shafts needed to be repaired due to excessive wear. This can be avoided with Thordon’s products,” said Bright.
According to Thordon, when RiverTough bearings are used by workboats, they routinely provide wear rates of 0.003” to 0.004” (0.075mm to 0.100mm) in 6,000 to 7,000 hours of annual use on the Mississippi River.
This upgrade was the first ship-assist tug in the New Orleans Port to change over to Thordon.
“We proposed retrofitting the RiverTough tailshaft bearing in conjunction with a ThorSleeve hardened shaft sleeve, and a TG100 shaft seal. This is a much more suitable shafting solution for vessels operating in abrasive rivers like the Mississippi,” Bright stated.
However, during discussions with the owner it emerged that a different installation method was required.
The traditional approach of casting Chockfast (an epoxy resin) directly to the outside diameter of the bearing meant that the Chockfast resin had to be chiseled out each time the existing rubber bearing needed replacing.
A new rubber bearing would have to be installed every 18 to 24 months. The bearing would have to be aligned and new Chockfast cast around them. This added to the time that the vessel was docked for repairs, which in turn meant additional costs.
Thordon’s solution was to create a permanent housing using the Chockfast epoxy grout.
Thordon worked with the shipyard to manufacture a mandrel (a dummy plug) to replicate the outside diameter of the bearing. This was coated with a release agent to prevent the Chockfast from sticking to the bearing. The plug was laser aligned in the strut and then Chockfast was poured around the mandrel. Once it was cured the plug was removed, leaving a perfect housing for the RiverTough bearing. The bearings were then installed in the new Chockfast housing by shrink fitting it with liquid nitrogen.
“This method of installation creates a permanent bearing housing that can be reused with a replacement bearing should it be needed without the cost of installing new Chockfast,” said Bright.
The same technique was used on the rest of the vessels in the series.
The first tug has been operating with RiverTough bearings and TG100 shaft seals since November 2015 and has gone through at least one docking cycle without having to replace the bearings.
Thordon Bearings completed the conversion of the fifth and final vessel in the series for the owner in April 2020.
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