Like many of you, I've huddled down in the engine room with the coupling backed off obsessing over a few thousandth's of an inch difference with the feeler gauge and wondered how critical it is. I finally got an answer, at least for the single bearing in the strut powertrains I've always favored and used in most of the boats I designed.
We hit something about 1000 miles ago in the Erie Canal. We never saw it but there was the kind of huge bump and jump that makes you run down and see if the bilge pumps are running. Everything seemed fine until the next day when I noticed some vibration when I brought the RPM a couple hundred above our normal cruise. It wasn't too bad but I could hear a knocking sound on that side in the aft cabin over the shaft strut on the side of the impact. I also noticed that the shaft could no longer be turned easily by hand with the coupling.
We were up against the winter closure of our marina in Albany (got out two days before the dock was pulled) and the boat was generaly running fine so I decided to have it looked at down south. We had a nice run to Florida. The knocking got slightly worse when we ran harder than normal but the Cutlass bearings had looked close to needing replacement when we bought the boat in Detroit in September. I figured the vibration was wearing the starboard one out faster.
We finally hauled and were shocked to see this:
(I don't know why but this site is flatly refusing to let me post photos the way I have been for years. Neither the "Insert Image" button nor the [img][/img] coding work. The public FB album is at this link.)
Put the edge of a piece of paper along the shaft on your screen. That curve isn't an effect of the camera, it looked even worse in real life.
The shaft was moved all the way over to the side of the stern tube and was rubbing on the hull. That was the knocking I heard.
You can see the scars on the keel where something like a big deadhead wedged itself between the hull and shaft.
The big mystery is why there was not more prop damage, nothing visible but it certainly needs to be checked out.
I never would have run the boat so long if I had any idea it was in this condition but it is probably a good thing we did. I am tremendously impressed with Oasis Boatyard and Marina in Saint Augustine and confident they will be able to make this right.
I expected to find that either the shaft or the strut were slightly bent and would need some attention but nothing like this. I think the degree of deformation may have masked the problem because everything was under so much tension that it couldn't vibrate. It is a testament to the resilience of Cutlass bearings.