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Offshore Towing considers fleet refurbishment

Wed 11 Oct 2017 by Martyn Wingrove

Offshore Towing considers fleet refurbishment
Thordon Bearings’ TG100 seal on Zion Falgout can turn with the shaft, causing no damage or wear

Offshore Towing is considering retrofitting its fleet of tugs and supply vessels with new shaft seals and other components after success with one of its oldest units. It operates a fleet of six ocean-going tugs and two supply vessels, providing towage and support services in the Gulf of Mexico and Bay of Campeche, Mexico.

The Louisiana, US-headquartered tug operator has upgraded a 1974-built tug at Conrad Deepwater shipyard, in Morgan City, Louisiana. It extensively refurbished 9000 hp (6700 kW) tug Zion Falgout at the shipyard during Q3 2017. This involved retrofitting TG100 seals from Thordon Bearings to the propeller shafts. These seals were almost 300 mm diameter, making them the largest TG100 series seals that Thordon has ever supplied.

Zion Falgout is a twin-screw workhorse tug with 67 tonnes of bollard pull. It has been using the TG100 seals for several weeks. Offshore Towing operations manager Henry Bailey said that depending on the performance of the TG100 over the coming months, other vessels in the fleet of tugs and supply vessels would be retrofitted with the Thordon arrangement.

“We were introduced to the TG100 seal by United Tugs, which has operated the system for a number of years without problem,” he said. “The TG100 seal has been operating successfully so far and although too early to provide a full appraisal, we are very satisfied and do not anticipate any problems.”

During the retrofit, Thorden removed stuffing and packing boxes that prevented water ingress to the engineroom and replaced them with TG100 seals, which turn with the shaft, causing no damage or wear.

Thordon worked with E J Fields Machine Works and Conrad Deepwater on the retrofit. The forward end of the shaft line was undercut and then clad-welded with stainless steel to prevent corrosion after which the shaft was returned to its original size. This gave the seal a smooth corrosion-free surface on which to operate. E J Fields also fabricated a mounting plate which the yard welded to the stern tube.

The primary seal uses hard wearing, silicon carbide faces and Thordon’s proprietary elastomeric bellows to provide an unlimited shelf life compared to rubber-based bellows, which need periodic replacement.

It also features a unique secondary seal with a return-to-port capability. In the unlikely event that the primary sealing surface is damaged, this emergency function allows the shaft to turn at reduced speed enabling the vessel’s safe return to port for repairs.