A friend of mine recently had his Catalina 30 pulled from the water and the aft lifting strap was on the propeller shaft between the hull and the strut. It appears to have about 1/4 inch of T.I.R. He wants to get on with the season without replacing or repairing the shaft. Opinions: What, if any, is an acceptable amount of shaft runout. The length of the shaft in this area is about 30 inches.
Prop Shaft runout
- Thread starter Sutric
- Start date
Tir around .001- .003 inch is ok. .. o.250 is a bit too much. It can be straightened in place by marking the high spot and bending it using wooden wedges against the hull. Not a good fix but if carefully done can get him through one season.
Good way to separate the strut from the hull. If the shaft is SS with a 1" shaft, prying the shaft with wedges will very likely lift the strut off enough to get it leaking. Bronze shaft, maybe. This is boating maintenance at its absolute worst.
Better to start out like this :
Appreciate your comments. I do want to mention that the sling positions are marked on the boat already, but the design of the keel (pretty swept back) and the prop shaft (really far forward) do make it difficult to get them correctly positioned. The year before the strap got hung up on the trailing edge of the keel and there was only about 3" of strap carrying the weight. Here is a picture of the arrangement. The question is how much trouble my friend in by using this bent shaft for at least this season. 
Sounds like a real bugger to get the sling properly positioned.
No measurements or material are supplied here but IMHO, either the strut could be damaged in trying to correct the bend in the shaft or the fact that it's doubtful the shaft could be straightened out enough to make it turn smoothly while under way.
If the strut is deformed in this bending attempt, I doubt he will get the boat out this summer. Just not worth the high risk.
I am not aware of what the tolerable TIR (total indicator runout) is for a shaft with 30" between supports but it is more than angular misalignment between the shaft flange and transmission flange which is about 0.001" per inch of flange diameter or 0.004" on a 4" flange. And that's really a rough and dirty alignment job. I always try to keep mine less than 0.002". Fortunately, the angular alignment only needs a touch up maybe once in 5-10 years if the boat always stays in the water.
Is the yard taking any responsibility for the shaft bend due to improper sling placement to the marks? You should talk to your insurance company.
IMHO, you absolutely want it fixed correctly, regardless of the amount of work to do so.
IMHO, you absolutely want it fixed correctly, regardless of the amount of work to do so.
It's sort of a messy situation right now. The yard did say they would correct it by replacing the shaft after the boat was pulled last fall but they never "got around to it". Now they are asking the boat owner to put the boat in and try it out. They say that if the vibration is too bad, they will replace the shaft. Makes me upset to see this. I don't know why my friend is going along with it. We've suggested going to his insurance company and even offered to help him pull the shaft in order to measure it but he wants to try it out anyway. Oh well....
Before trying it I’d try to get the yard to agree (in writing if possible) that they’ll also be responsible for any further damage caused by the deformation. Fear of transmission or strut issues might motivate them to replace the shaft.
Pretty lousy of them to have “forgotten” about it until springtime when your friend would be motivated to try to ignore the problem and go sailing.
Pretty lousy of them to have “forgotten” about it until springtime when your friend would be motivated to try to ignore the problem and go sailing.
