The U.S. Coast Guard (USCG) operates two Polar Class Icebreakers, the POLAR SEA and POLAR STAR. They have a length of 399 feet and a displacement of 13,500 tons, and are also the most powerful nonnuclear icebreakers in the world, with a maximum rating of 3 x 20,000 shaft horsepower. Each propeller shaft is supported by two water lubricated sterntube bearings. The bearings are a dove-tail slot stave design. Both the aft and forward bearing materials are Thordon XL (Polymer Alloy). The bearing housings are supported by five lands that are integral with the stern bossing. The severe operating environment has caused erosion to the lands due to fretting and corrosion resulting in insufficient support of the bearing housing. Because of concerns about welding on the large HY-80 casting previous efforts to restore fit of the bearing housings has relied on build up of the lands with Belzona Super Metal (a machinable grade metallic polymer). For this application the lands have been repeatedly undercut and boring undertaken to restore fit. Using this method of repair has proven to be short lived and expensive to maintain. A project was undertaken to develop a permanent repair and/or redesign that would effectively address the loss of fit as well as provide for a reliable bearing. The bearing design arrangement was examined, with particular attention to considerations for ice-class service. The properties of potential chocking and bearing materials were assessed. Modifications to the bossing and bearing length were also examined. This paper presents the results of the study.

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