Leading International Maritime Magazine

Offshore Towing opts for Thordon shaft seal after competitor recommendation

Offshore Towing Inc (OTI) has successfully completed the extensive refurbishment of its 1974-built 9000hp-class tug Zion Falgout at the Conrad Deepwater shipyard, in Morgan City, Louisiana, U.S.A.

The milestone project involved the retrofitting of TG100 seals in what marks OTI’s first mechanical shaft seal installation and the largest diameter TG100 series seals ever supplied by Thordon Bearings. An 11.75in (298mm) diameter seal was installed to each propeller shaft of the 66.88t bollard pull twin-screw workhorse.

“A primary factor in OTI specifying the Thordon solution was to eliminate the need for stuffing/packing boxes,” explained Jim Bright, Business Development Manager, Thordon Bearings. “This really is an out-dated system for preventing water ingress to the engine room. If the packing box is not adjusted correctly the amount of water ingress to the vessel can be catastrophic. Packing can also result in excessive wear of the propeller shaft, which could require drydocking to remove the shaft and repair the damage. A TG100 seal turns with the shaft, causing no damage or wear.”

During the retrofit, Thordon Bearings worked with E J Fields Machine Works and Conrad Deepwater, both in Morgan City, to expedite the installation. 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.

Henry Bailey, Operations Manager, Offshore Towing, said: “We were introduced to the TG100 seal by United Tugs, which has operated the system for a number of years without a problem. So, we thought we’d give it a try. The TG100 seal has been operating successfully so far and although too early to provide a full appraisal, we are very satisfied and don’t anticipate any problems.”

Depending on the performance of the TG100 over the coming months, Bailey said it is likely that other vessels in OTI’s fleet of tugs and supply vessels will be retrofitted with the Thordon arrangement.

The TG100 is a mechanical seal specially developed for 86mm (3.375”) to 305mm (12”) water lubricated propeller shafts typical of workboats, dredgers, tugs, yachts, patrol craft and other coastal vessels operating in either clean or dirty, abrasive waters.

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 “Return to Port” capability. In the unlikely event that the primary sealing surface is damaged, this emergency function allows the shaft to turn at a reduced speed enabling the ship’s safe return to port for repairs.

While the OTI order represents the largest TG100 seal supplied, Thordon Bearings also manufacturers the SeaThigor seal for operators of larger diameter water lubricated propeller.shaft systems