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THORDON TOWBOAT RETROFIT "DEFIES THE LAWS OF PHYSICS"

Tuesday, June 23, 2020 

Excessive bearing and shaft wear resulting in frequent drydockings has led a Louisiana-based workboat operator to improve operational competitiveness and ensure greater equipment usability by converting to a Thordon RiverTough tailshaft system.

Thordon has performed a RiverTough bearing conversion for an undisclosed opertaor, to a twin-screw towboat running on the lower Mississippi with 6in (152.4mm) Aquamet diameter shafts and 6in rubber bearings.

Thordon sales manager Jim Bright said: “The increased tailshaft maintenance costs combined with lost charter days as the vessel required drydocking before its normal docking schedule led this particular operator to ask Thordon for recommendations on how best to reduce life cycle costs. We are finding a lot of towboat owners, running rubber strut bearings directly on stainless steel or Aquamet shafts, are experiencing excessive shaft and bearing wear resulting in drydockings every 18 months or so, at significant cost."

To improve performance, the rubber bearings could be replaced by Thordon’s RiverTough which would solve one issue but Bright pointed out this would only address half the problem, “the shafts would continue to wear as before”.

To solve this problem and mitigate against the abrasive effects of the Mississippi River, it was decided that a Hardened non-corrosive NCB ThorSleeve would be fitted over the shafts. With the addition of ThorSleeves, the shaft would be able to deliver longer life to match the RiverTough Bearings’ performance. However, this was not so straightforward because the addition of the sleeve would increase the shaft’s diameter to 6.5in (165.1mm).

“To accommodate the larger shaft diameter a larger bearing had to be installed,” said Bright. “But fitting a larger bearing into a strut designed for a 6in bearing would require a considerable amount of line boring and modification work or the need to completely replace the strut, which in the past was the only way to undertake this kind of project. Both of these options come with a high price tag making the upgrade hard to justify, so rather than modifying the struts, we found an alternative solution that cheated the laws of physics.”

Thordon’s engineering team designed a bearing that could accommodate the larger shaft while fitting into the original housing, without impacting the bearing performance or its abrasive resistance qualities.

“In effect we fitted a bearing designed to go in a housing for a 6.5in shaft into a housing designed for a 6in shaft. The solution saved approximately US$10,000 in line boring and machining work, while also giving the workboat operator a tailshaft bearing system capable of lasting for years rather than months.”

According to Jason Perry, Thordon Bearings’ Territory Sales Manager, the project is nearing completion at the dockyard of Ashton Marine LLC in Harvey, Louisiana and Thordon will now carry out the same process on a second vessel in the operator’s eight-strong fleet. 

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