Catalina 27 + how to ensure the prop shaft is true

[nigglesworth]

I am about to head into my second season and would like to test my prop shaft before it goes into the water. At the end of last season, a fateful trip lead to a mooring ball being swept under the boat, past (colliding) with the prop while backing out of a mooring.

I will spare you the details, saying only that an otherwise uneventful season perhaps lead to a little overconfidence on my part. I checked for prop damage (none). Under power, I do not notice any unusual vibrations or strain, but I do notice that the boat bear's down slightly when it nears hull speed (5kn). This partially submerges the exhaust hole, which used to remain out of the water.

A) should I be concerned?

B) is there a way to test the shaft without pulling it? (This requires me pulling my rudder so I want to be sure this is necessary). I have just begun replacing my seacocks and this will certainly add to my spring list.

Any input or suggestions would be greatly appreciated!

[mitiempo]

Is there any vibration at any rpm that did not exist before the mooring ball incident? That would be one indication.

[SlowButSteady]

With the boat on stands, and the engine in gear (but turned off), have an assistant turn the engine by hand while you very carefully watch the strut. If the strut appears to move at all as the shaft turns, or if the prop blades or any part of the shaft look like they're "wobbling", then the shaft is suspect. You can also lay a light board across the shaft on the inside of the boat (one end resting on the hull); if it moves up and down at all while the shaft is turning the shaft is suspect. If it passes those tests, look for vibrations (as mitiempo said). Pull the prop (for safety), hook up some cooling water, and fire up the engine. If there is a really bad vibe (particularly associated with the strut), or the end of the shaft doesn't appear to be spinning with an essentially fixed axis (there's often a little dimple in the end of the shaft you can watch for movement), then the shaft is suspect. If you can't see any other obvious reasons for the drivetrain not passing the above tests (bad cutlass bearing, alignment problems, history of marine gremlins, et cetera), it's probably time to pull the shaft.