Water-Lubricated COMPAC Sterntube Bearing Retrofit Benefits Bulker
25 September 2006
Canada-based Thordon Bearings Inc. has designed and manufactured pollution-free bearing systems for over 25 years. Its water-lubricated COMPAC bearings, which eliminate the sterntube oil and the aft seal, are increasingly popular for newbuilding and retrofit projects.
In mid-2005 CSL International Inc. (CSLI) invited Thordon Bearings to study the existing oil-lubricated sterntube system of its recently purchased 23 year-old tanker Cabot. The US-based company, part of Canada's CSL Group, planned to convert the ship into a self-unloading bulk carrier at the Shan Hai Guan Shipyard in China.
A key element of the project specification called for the conversion of the original oil-lubricated whitemetal propeller shaft bearings into a water-lubricated system guaranteeing zero risk of oil pollution from leaking sterntubes.
After reviewing all the drawings, Thordon prepared a conversion design proposal for CSLI, which then worked with the yard to finalise the project. All preparatory work was carried out while the ship was still afloat, and conversion of the existing system and installation of the Thordon COMPAC water-lubricated propeller shaft bearing system completed during dockings for the forebody conversion.
A new water-lubricated system was designed for a propeller shaft diameter of 590mm and a shaft liner diameter of 645mm, the COMPAC bearings having length/diameter ratios of 2:1 aft and 1:1 forward.
Support for the yard, owner and Thordon was provided by Thordon's authorised distributor in China, Proco Marine Technology & Eng. Co. Ltd. Thordon's manager of engineering, Ken Ogle, who oversaw the project from start to finish, was also present during the system installation.
The overall conversion project was completed in March 2006, the former 67,208 dwt tanker Cabot emerging as the 74,000 dwt bulker CSL Acadian and arriving on the US west coast in mid-April.
"Thordon's approach and understanding of this project's needs were first class and their expertise in this field contributed to a smooth and fast turnaround" said Mr. Louis Martell, Vice President Technical Operations of CSLI.
Delivery of the bronze liner, seal and Thordon Water Quality Package took two months. Based on the Cabot/CSL Acadian project, a sterntube conversion can be easily completed in 2 weeks to 10 days if all parts are at the shipyard. Projects can be conveniently scheduled to match the tailshaft survey cycle.
In planning conversions from a whitemetal/oil-lubricated system to a COMPAC system, Thordon requires details of the existing sterntube and shaft arrangements, bearing drawings, shaft alignment and loading calculations, and the tailshaft drawing.
A typical project calls for: assessment of the original bearing loading condition; conversion design package and work procedure paper; Thordon COMPAC water-lubricated bearings; bronze shaft liners; class-approved shaft coating; water-lubricated forward seal; and a Thordon self-cleaning Water Quality Package.
In a Thordon COMPAC bearing system, sea water is typically pumped by a maintenance-free self-contained pumping set from a sea chest through the Water Quality Package, which removes abrasive solids from the water supply (down to 40-50 microns) and ensures a flow for bearing lubrication and cooling. The flow is monitored by low flow alarms. Water enters the forward seal, flows through the COMPAC bearings and exits at the stern of the ship (there is no aft seal).
A Classification Society-approved that Thor-Coat shaft coating can provide tough corrosion protection for the propeller shaft, extending the period between shaft withdrawals.
Shaft liners are typically produced from gunmetal, 70/30 copper nickel or Inconel 625 materials. Only a forward seal is required, which can be a face seal, lip seal or stuffing box.
Operational benefits for shipowners in specifying a Thordon COMPAC water-lubricated bearing system at the newbuilding stage or by retrofit include:
- Zero pollution risk (oil is eliminated from the sterntube)
- Controlled bearing environment using the Water Quality Package, guaranteeing a 10-year bearing wear life
- Reduced seal maintenance costs (forward seal only)
- Ease of maintenance
- No emergency dockings (long predictable wear life)
- Survivability (non-catastrophic failure mode allows ship to get to port)
Among over 460 diverse commercial and naval references for its water-lubricated COMPAC propeller shaft bearings, Thordon highlights:
- Seven (plus three on order) Princess Cruises' ships, including Grand Princess, equipped since 1998
- Chemikalien Seetransport's LNG carrier Cinderella (since 1996)
- Algoma Central Corporation's tanker Algonova (since 1997)
- Gypsum Transportation's bulk carrier Gypsum Centennial (since 2000)
- Disney Cruises' Disney Magic and sistership (since 1997 and 1998)
- Two Grimaldi Group cruiseferries (since 2001)
- Four BP Shipping tankers; Moby Lines' ferry Moby Rider (since 1997)
- Three Staten Island ferries; and 12 Flinter Groningen-owned feeder container ships
