Thordon Bearings has unveiled what is potentially the marine industry’s safest, most robust shaft seal as part of a programme of enhancements underway to optimise its award-winning COMPAC seawater lubricated propeller shaft bearing system.
Targeting high quality, low leakage, long life and minimum maintenance, Thordon’s new SeaThigor forward seal was unveiled at SMM this week. Its outstanding technical features raise the bar in dynamic and static seal design, with an unmatched performance of the primary dynamic seal, and an ingenious secondary seal module that provides a Safe-Return-To-Port capability in the event of a face failure of the primary seal.
After several years of development and testing, the new SeaThigor safety seal design incorporates a pneumatically activated inflatable element to stop water ingress along the shaft, allowing for the repair of the main seal whilst at sea, or allows for the shaft to turn at a lower speed so the vessel can safely return to port for primary seal repair or replacement.
Providing a new level of redundancy to single screw or mission-critical vessels operating seawater-lubricated propeller shafts, SeaThigor can function as both a dynamic and static seal to provide water-tight integrity around a shaft, while allowing the propeller shaft to rotate in both directions across a range of shaft speeds.
With inside the engine room application and typically mounted on a rear bulkhead or stern tube flange, the modular design incorporates two wear-resistant silicon carbide seal faces that contact each other to provide primary static and dynamic sealing.
The seal is designed with an enclosed housing protecting the rotor components, so no moving parts are exposed, resulting in installation simplicity and requiring minimal maintenance. Its “all-metal” construction made of marine-grade bronze also guarantees corrosion resistance for life.
“The SeaThigor abrasion resistant sealing faces achieve dynamic sealing with leak and maintenance free operation,” said Andy Edwards, Thordon Bearings Commercial Director. “If there was ever a true fit-and-forget system, then SeaThigor is it.”
Suitable for 300mm (11.8”) to 650mm (25.6”) diameter water-lubricated propeller shafts, the seal features a series of precision compression springs that are unaffected by water temperatures, pressure or draught. These springs are used to linearly load the seal faces, ensuring that the pressure is equally distributed to the entire contact surface.
Unlike other water-lubricated stern tube seals which adopt an “inside pressurised” design, the SeaThigor is designed to operate with a hydraulically-balanced, outside pressure to better withstand higher water drafts and pressure variability in rough seas. This “outside pressurisation” design also counters the natural outflow direction through the rotating seal face, further reducing leakage.
Since both the static and safety sealing elements use Thordon’s proprietary elastomer technology, shelf life concerns are allayed with a much longer service life than traditional rubber seals.
This was affirmed during Lloyd’s Register Type Approval trials last year when two 443mm (17.44”) shaft diameter SeaThigor seals were tested simultaneously on the Thordon Marine Seal Test Rig, in Burlington, Canada. After extensive testing, the Safe-Return-To-Port emergency seal showed no sign of wear after 15 days of use. SeaThigor received LR and DNV-GL Type Approval this summer.
“Thordon Bearings will install the SeaThigor to an undisclosed vessel during a scheduled drydocking later this year,” said Edwards.
“We are seeing a resurgence of interest in seawater lubricated propeller shaft bearing systems and the SeaThigor is an important part of this. Market interest so far has been beyond expectation, with a number of commercial ship operators making tentative enquiries,” he said.