It has been Coast Guard policy to use water-lubricated propeller shaft bearings for all conventional propulsion shafts because we are able to get sufficiently reliable service from water-lubricated bearings and we avoid the leakage problems that inevitably occur with oil lubricated systems particularly when there is no drainable void separating the two sealed fluids. All seals leak eventually and their life can be very short when exposed to abrasives. Arctic waters can be fairly abrasive, so, there is greater risk of seal failure. For icebreaking service there are likely vibration benefits from use of elastomeric bearing materials as well.
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