British Columbia Ferry Services Inc. operates five "C" class passenger-car ferries that were delivered in 1976 (3 ships) and 1981 (2 ships). The vessels have a service speed of 19.0 knots, are 457 ft. long, and have a gross tonnage of 6,550 tons. They have a capacity of about 360 cars and 1,500 passengers. Their route varies from Vancouver-Vancouver Island-Sunshine Coast, with up to 9 round trips per day. The vessels have a double-ended single screw propeller configuration. Each of the controllable pitch propellers are driven by one or two diesel engines rated at 5,930 HP, through single reduction gearboxes. The two gearboxes are connected via quill shafts that are concentric with the pinion shafts. The pinion shafts are engaged via clutches at the end of each of the quill shafts. This arrangement enables one or both of the diesel engines to drive either one or both of the propellers. In 1998 a catastrophic failure occurred to the bull wheel on one vessel. The bull gear teeth broke off taking out both pinions. In 1999 the bull gear on another vessel was replaced as a result of fractured gear teeth, found during an inspection. In addition, a number of failures have occurred to both the lineshaft and pinion shaft bearings. An investigation was conducted to determine the source of the failures and the most prudent and economical course of action. To accomplish these objectives a review of the system design and maintenance/failure history was conducted, as well as theoretical modeling and alignment and vibration measurements. It was found that the failures occurred due to misalignment. A realignment program has been undertaken, with the first realignment completed in February 2002. This paper describes the failure investigation and the results of the realignment work conducted.

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