Prop or Coupler

"Last summer, while backing up

"Last summer, while backing up to set the anchor, I hit the only rock in a little bay on our lake, and tore the tips off the prop..
Now, I raised the o/d to replace the prop with a 17pitch mystery prop that came with the boat (it had a little ding, but a few taps, and a file fixed it right up).. When the o/d came up, a split in the bellows reared it's ugly head,(yup, a black cloud hung over me for a bit) I drove slowly back to the marina, and hauled the boat out. Had all the bellows & gimble bearing replaced, put the o/d back on, and took it out for a run.. The mystery prop was still on the O/D and I had never run it up before! As the RPM came up near 2000, the stern started to shudder like the engine had a terrific miss.. It stopped about 2300 RPM, but felt like some power was missing.. I took the mechanic from the marina out for a spin, to feel the vibes.. Like going to a dentist with a toothache, the vibration was gone, although the boat still seemed sluggish.. Dropped the mechanic back off, and went out again.. The vibration was back..
Now, My first thought was the prop hub slipping, and my worst thought was the drive coupler slipping..This was a instant problem, the boat had never suffered a loss of power or vibration before I put this mystery prop on..I have no experience with this type of problem.. I sent the prop out for repairs, told them to check the hub and let me know if that was the problem, but this information was never attached to the prop, so they welded up all the blades, and made it look pretty.. I called them to ask if they kept any records on the work performed, and they told me they 'only' check the hub when asked, and no one asked on the work order..So it's STILL a mystery prop, that could have a spun hub!! Now, I can put another prop on it, (it hasn't been launched this season yet) but I hate to launch it, then have to haul it back out to fix a drive coupling.. In the vast experience of the folks here, what are the chances that the problem is the drive coupling, and not the prop? Do couplers go 'instantly' like that without warning? There was no visible problems with the spline on the OD (had it all re-sealed while it was off). Is this what either of them feel like when going/gone? can they be intermittent like this? I feel like a hypochondriac fearing the worst, but it may only be a rash? The boat is a 1989 23' ebbtide mid cabin, w/ 5.7 and alpha 1 OD with only about 340+ hours on the engine (and coupler)"

"First thing I would do before

"First thing I would do before having a heart attack is borrow a known good prop of any size that will fit, and try that out. (You should carry a spare prop anyway.) If it still does its thing, it is likely the coupler. Alpha couplers are not as robust as Bravos, and this kind of thing can happen.
Unfortunately if it's the latter, the drive leg and the engine will have to be pulled to replace it. Big job, but not complicated for a shop. Make sure they check the alignment on re-installation.
Rod"

"Rod and Bill:
The mystery

"Rod and Bill:
The mystery prop should have been balanced by the reman. shop and it seems they would have found the damaged hub during the balancing process. What about a bent prop shaft since he struck a BFR (Big Fat Rock). Also, wouldn't the U-Joint failure cause the vibration? Guy"

"Bill
If it was a one minute

"Bill
If it was a one minute it wasnt there, next it was type vibration, I would not panic to much untill you try a known "GOOD" prop on her.
Its much cheaper and easier to fit a prop and try it than to pull the outdrive and engine on a hunch
that the coupler may be gone.
Start with the simple things first, then work your way in if you have to.
Regards
Peter C"

"I have another prop here, I&#

"I have another prop here, I'll put it on before I launch the boat. If theres no vibes, I'll know it's the prop..(but that won't be for a couple of weeks) the stub' half of the universal was replaced when they did the seals in the OD after I found the rock.. 'Would' the bad hub really become apparent when they balanced the prop? I don't imagine they really torque it.. There was no vibration until the prop really started biting the water, then none again after it was at 2500 or so.. Just spinning the prop by hand shows no variance or wobble in rotation..I will check the shaft, I believe the limit is 7 thou? how far out the shaft would you mic. the variance in rotation? Near the end, halfway, or near the seal? The vibration was really shaking the boat, how far off would the shaft have to be to make the vibration that noticeable? It would seem, that from the way it was shaking, if a bent shaft was causing the problem, it might be pretty noticable?"

"Couldn't take the suspenc

"Couldn't take the suspence any longer.. My boat is on a trailer out infront of my shop, so I went onboard, and jumped down into the engine compartment.. I may be wrong, but it seems to me that if the coupler was going, there would be 'some' evidence on it or from it someplace! I reached down inside, and ran a q-tip all around the face of the coupler where the shaft enters.. Pulled it out and took a good look at it.. No grit, no rubber shards, no metal dust, no burnt smells, nothing but grease.. I would think if the coupler was shot or even going, there would be 'some' crud from the breakdown coming out and collecting in the grease, where else would it go?
Thats given me a better feeling, I hope it's not false security.. I just don't want to launch it, and then have to pull it out again. The launch site is handy to my house, but 15 miles from the marina where I will be keeping the boat. I have to rely on others to take it there, launch it and mabe haul it back out, because I don't own anything that will pull it.."

Take a real good look inside t

Take a real good look inside the prop hub for some junk you may have sucked into the prop that may add enough weight to knock it out of balance. Like a growth of zebra mussles or chunk of wood or a rock.

"Nope.. That particular prop h

"Nope.. That particular prop had not been used for more than a year.. It was one of two 'spares' that came with the boat. I contacted the previous owner to see what he knew about the prop.. He told me that the one on the OD was the best one, because he could not get a decent hole shot with either of the others. One of the others, was this one, and it was exactly the same as the one on the OD, same dia, same pitch.. It should have been every bit as good.. The 'other' one he said would not give him a decent holeshot was a 25 inch pitch prop.. He did not seem to know 'why' it wasn't any good.. ha.. I would be surprized if he even got it to 3000 rpm.. But the fact that he told me the 17 inch was also not performing, would seem to indicate it had a problem.. If he was just trying holeshots with it, he probably never got it to vibrate while slipping, it probably went right to a hub spin, and no power.. Seeing every thing else looks ok, I'll put the other 17 prop on, and launch it in a couple of weeks and see what happens.. Thanks for the feed back folks.. Hopefully, all is well and I'm only out 130 bucks for the incomplete prop rebuild.."

"Bill;
I think you are on the

"Bill;
I think you are on the right track.
The prop shaft would have to be bent a large amount to cause that kind of vibration, and then it would be continuous, varying only with engine speed."