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.
!/4 inch of bend is absolutely unacceptable. It will tear up the cutlass bearing and likely cause a leak at the stuffing box, It will probably cause the shaft to rub on the shaft log and damage that as well. No way you can bend that saft in place to straighten it. To straighten a shaft you have to bend it beyond the yield point in the opposite direction. Since materials have springback you will need to go further than 1/4 inch beyond straight in the opposite direction and hope it springs back to straight. totally trial and error. To straighten bars they make special presses with dial indicators along the bar and support points to simply support the shaft. Once straightened you need to stress relieve that material to eliminate residual stress in the material that can cause it to distort in service. As the shaft bent it probably damaged the cutlass bearing already and removing the shaft will allow a full inspection of the damage. Think of it bending. To bend it had to be supported on each end. One end was the cutlass bearing the other was the shaft log and/or the transmission. The shaft log could be cracked and the strut could also be bent out of alignment. Bending a 1 inch bar takes a lot of force and the stuff supporting the bar is not made for that.
Practical advice for the season - propeller shaft fell out of the coupling.
Bought at auction a 2002 Hunter 386, abandoned at a marina, but well winterized. Abandoned in 2013, bought by me 2017. No survey or inspection done ... in the sling, dropped in the water and woohoo, off we went. Noticed a coupling "key" in the aft cabin center shelf. Whatever. Also noticed in year 4 several of the engine mount bolts (the top ones that loosen the system, were undone about 1/2", so, some flexibility in engine vibration and rotation. ("Gee, what a surprise the coupling let go of the shaft!!")
7 years later, motor 8 miles from winter storage to summer marina, put it into reverse at slip, and the propeller shaft dropped out of the coupling in the middle of the lagoon. Cool! Of course, in the moment I had no idea what the problems was - out of oil? Transmission dead? Turned out. "just" the shaft escaping the coupling. I have now taken it apart and the coupling is buggered - grub bolts worn into the coupling, shaft has some scarring etc.
I now assume that the key was removed when stored by previous owners, and I was astoundingly lucky to get 200-250 hours on the engine over the my 7 years. So, now I bought a split coupling that seems a bit small to get on the old shaft. Can get in on maybe 1/4". Have a new key and will clean out the key channel in the shaft.
So, in my reading, I believe the proper way to fix all this is to tow the boat back to the crane, get her out of the water, drop the rudder, get a new shaft, hire a Nascar crew to face and set up the coupling with a new shaft. Not going to happen right now.
So, I seek practical advice to get me through the summer (another maybe 40 hours). I propose cleaning the shaft, maybe a little Dremel here and there, heat the coupling, get it on with the key, drill a new grub/set screw hole. I expect to be able to get the coupling on the shaft securely. Then position it against the transmission coupling and assess gaps. BUT, there is no way I am going to get to 3 thou, or even 10 thou. I might raise/adjust the engine mounts to better line it all up, but again, the shaft with the coupling has the ability to wiggle easy 1/4" from the entry into the interior of the boat. Maybe the cutlass bearing is a bit worn as well? But with that 1/4" play, I figure the system is offering some flexibility. I expect in the winter to to the proper things, and get it right, may even have to buy another coupling if the system I assemble is too wobbly. New shaft, cutlass and coupling with machining together in the winter.
Thoughts please?
Hamish
Bought at auction a 2002 Hunter 386, abandoned at a marina, but well winterized. Abandoned in 2013, bought by me 2017. No survey or inspection done ... in the sling, dropped in the water and woohoo, off we went. Noticed a coupling "key" in the aft cabin center shelf. Whatever. Also noticed in year 4 several of the engine mount bolts (the top ones that loosen the system, were undone about 1/2", so, some flexibility in engine vibration and rotation. ("Gee, what a surprise the coupling let go of the shaft!!")
7 years later, motor 8 miles from winter storage to summer marina, put it into reverse at slip, and the propeller shaft dropped out of the coupling in the middle of the lagoon. Cool! Of course, in the moment I had no idea what the problems was - out of oil? Transmission dead? Turned out. "just" the shaft escaping the coupling. I have now taken it apart and the coupling is buggered - grub bolts worn into the coupling, shaft has some scarring etc.
I now assume that the key was removed when stored by previous owners, and I was astoundingly lucky to get 200-250 hours on the engine over the my 7 years. So, now I bought a split coupling that seems a bit small to get on the old shaft. Can get in on maybe 1/4". Have a new key and will clean out the key channel in the shaft.
So, in my reading, I believe the proper way to fix all this is to tow the boat back to the crane, get her out of the water, drop the rudder, get a new shaft, hire a Nascar crew to face and set up the coupling with a new shaft. Not going to happen right now.
So, I seek practical advice to get me through the summer (another maybe 40 hours). I propose cleaning the shaft, maybe a little Dremel here and there, heat the coupling, get it on with the key, drill a new grub/set screw hole. I expect to be able to get the coupling on the shaft securely. Then position it against the transmission coupling and assess gaps. BUT, there is no way I am going to get to 3 thou, or even 10 thou. I might raise/adjust the engine mounts to better line it all up, but again, the shaft with the coupling has the ability to wiggle easy 1/4" from the entry into the interior of the boat. Maybe the cutlass bearing is a bit worn as well? But with that 1/4" play, I figure the system is offering some flexibility. I expect in the winter to to the proper things, and get it right, may even have to buy another coupling if the system I assemble is too wobbly. New shaft, cutlass and coupling with machining together in the winter.
Thoughts please?
Hamish
Having done several alignment "touch ups" on my originally purchased '99 H-310 over the years, the very first thing I would be concerned with when dealing with your new split shaft coupling is to check the flange face for being 90° +/- to the prop shaft. That will determine how accurate an angular alignment you can achieve.
Be careful what error you are willing to accept because you may be looking at serious transmission damage with all the mis-alignment you've lived with to date.
I still have to agree heavily with @JoeWhite in that you may be causing $$$ damage on other parts by trying to live with what you've got.
Be careful what error you are willing to accept because you may be looking at serious transmission damage with all the mis-alignment you've lived with to date.
I still have to agree heavily with @JoeWhite in that you may be causing $$$ damage on other parts by trying to live with what you've got.
I had a C30 that was on sea trial before a sale. Had some vibration at 3000 rpm. Didn't think too much of it. Had a small trickle of water coming from aft that the buyer was questioning. We traced the leak to the strut bolts. There is no way I had 1/4" runout to cause the issue. The actual construction of the strut interior patch over the strut bolts was nowhere near the factory drawing. Ended up having to remove the fuel tank (vibrating tool). The strut seal had opened.
IMO, the shaft cannot be used as-is without risk of causing other damage, (strut leakage, packing leaks and excessive wear, cutlass bearing wear, and possible transmission damage)
By comparison, I had to change the shaft on my present B411 due to corrosion. Had a new shaft in a week.
IMO, the shaft cannot be used as-is without risk of causing other damage, (strut leakage, packing leaks and excessive wear, cutlass bearing wear, and possible transmission damage)
By comparison, I had to change the shaft on my present B411 due to corrosion. Had a new shaft in a week.
Decided that what I know to be true is true. There is really only one way to do things properly, so, out of the water she comes after a 2-hour tow, pull the shaft, get a new one, add in a new Cutlass bearing and probably even a new PSS and >$2,000 later, it will all be done.