In-depth | BEARINGS
Thordon entices shipowners with COMPAC
Thordon Bearings of Ontario, Canada, has recently announced a 15-year bearing wear life guarantee for its COMPAC pollution-free stern tube bearings.
C
onfident that seawater lubricated propeller shaft bearings offer wear life predictability, Thordon
has offered this new incentive for shipowners to use its environmentally- friendly solution. As the propeller shaft bearing system
is seawater lubricated rather than oil lubricated, it has a far lower impact on the environment and the general ecosystem.
Technology COMPAC is a non-metallic, elastomeric polymer alloy
with a formulation
including special lubricants to provide low coefficient of friction. The loaded portion of the bearing is smooth, while the upper half contains grooves for flow of
the
water lubricant/coolant. This encourages early formation of a hydrodynamic film between the shaft and the bearing. Due to its elastomeric properties,
Thordon’s COMPAC stern tube bearings will deflect and then subsequently reject small abrasive particles, allowing them to be flushed through the bearing without becoming embedded. The shaft of the bearing system is
protected by a Thor-Coat modified epoxy resin coating, with no woven fabric component and is designed to wear for at least 10 years. As the overall bearing system is 50 times
more elastic than white metal and believed to be three times more compliant than other common non-metallic propeller shaft bearings, COMPAC deflects slightly under edge loading. COMPAC also has an increased
tolerance to misalignment. The load is spread, and the localised pressure on the bearing is reduced, eliminating the bearing wiping that often occurs under these conditions. The length/diameter ratio for COMPAC
18
Thordon COMPAC bearings in bronze carriers with single tapered keyset (credit: Thordon Bearings Inc).
can be as low as 2:1 for the bearing adjacent to the propeller and 1:1 for all others depending upon the load and operational requirements. By using Thordon Bearings’ technology,
ships trading in the world’s oceans and seas are now able to eliminate both operational and accidental stern tube oil pollution (STOP) while also reducing their operating costs, the according to the company. Zero tolerance for any kind of
ship-source pollution is now becoming the norm and international regulations are becoming more and more stringent. The Thordon COMPAC bearing system uses clean seawater as the lubrication medium and Thordon non-metallic COMPAC bearings in place of oil and white metal bearings. The seawater is
drawn in, pumped through the bearings and then returned to the sea. An added advantage is that the COMPAC bearing is split with a tapered key system that allows inspection of
the bearing and
shaft journal without pulling the shaft. The performance of sea water lubricated COMPAC bearings to date has been comparable to oil lubricated white metal stern tube bearings.
Applications Thordon’s COMPAC has already been installed in many different vessels including anchor-handling tug supply vessels from Bender Shipbuilding. The six anchor-handling tug vessels are 81m - long twin-screw ships with 286mm diameter propeller shafts. The stern rollers, which are the large drums fitted onto the open
Ship & Boat International November/December 2008
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