Finding and Curing Annoying Vibrations

Careful!

These audio interviews are candid conversations with highly experienced staff from our shop—people who have worked on boats for years. However, the content of these interviews does not imply any particular result on your boat nor extend our warranty in any way. Please contact us directly for specific project questions or bring your boat to the yard for a consultation.

Listen to “Finding and Curing Annoying Vibrations” now.

Mechanical Department Head Darryl Paddock of Townsend Bay MarinePersistent vibrations can loosen fasteners, rattle dishes, and threaten your sanity. Here are some thoughts on what to do before you get too many screws loose from Townsend Bay Marine's Mechanical Department Head Darryl Paddock.

What causes vibrations?

First place to look is your propeller. Recently we’ve seen a lot of propellers that are key-bound: the prop is tightened against the keyway instead of the taper. You only have to be off by as little as 1/16th of an inch to create noticeable vibration. Fortunately, it’s an easy fix: remove the excess material from the key until the prop will sit fully up on the shaft taper. Obviously, this is easiest to do if the boat is out of the water.

What else can make it shake?

Hitting stuff that floats or is under water is a common cause. Nicking or bending one blade of a propeller can set up a vibration that you will feel throughout the boat. Sometimes getting your propeller pitch modified will leave one blade slightly unequal in pitch or weight; good prop shops have programs to ensure equality. Swapping with a new prop of known quality can tell if your current prop is the source of the problem.

How big a factor is alignment?

Misalignment of the shaft to the cutlass bearing or transmission isn’t normally the source of vibrations, but can amplify them. Over time, however, the side loads imposed by a misaligned shaft can ruin a cutlass bearing, making everything worse. Ideally—with the boat out of the water—you would align the shaft in the shaft tube, then align the transmission coupling up to that. After that, it should be smooth sailing.