By definition, a shaft bearing (sometimes called a Cutless bearing) is a rubber-lined composite or brass bearing through which the propeller shaft turns, and as such, is the final component in the drivetrain forward of the prop. The cylindrical bearing generally has a grooved inner surface so water can flow through for lubrication. The bearing assembly also supports the shaft; when the bearing and the engine and shaft are correctly aligned, the result is vibration-free running under power. But what happens if you can wiggle the shaft, even a little? Or if you see uneven wear around the lip of the bearing, a telltale sign that the engine is out of alignment? The answer is simple: Replace the bearing. The task itself is a bit more complicated. But if your boat is hauled for the winter or for fresh bottom paint, now’s the time to tackle the job.