Prop Shaft Vibration

[solanderi]

First and foremost....our thoughts are with Genesis and the folks that just weathered through Dennis...we hope you and your families are safe and sound.

I recently ran over a 50# line and wire leader with the starboard prop. I ran the rest of the day with no problem but ended up doing a little dive time to clear it all off. The next time I went out, during an ER check I noted a pretty significant vibration on the same shaft. What is the trouble shooting algorithm for this?

[Genesis]

We're fine - we took about a 7 hour power outage, and still are getting rainbands and about 40kt winds, but the boat, house and people are all fine. No damage other than a bit of a mess in the yard, and a lot of work to put away all the boards and such (again).

My pool enclosure, which was damaged by Ivan and that I hadn't been able to get repaired, is probably a total. We stripped all the remaining screen before Dennis got here, but it didn't help - I now have structural damage where there were things bent before; I think I'm going to remove it and install a decorative iron fence instead - that won't get trashed by storms, and my kid doesn't mind the sun in the pool anyway. The enclosures are an expensive pain in the ass to keep up anyway and while they do cut down on the mess in the pool, its not THAT big of a difference.

Dennis was nowhere near as bad as I expected it to be. It was quite sporty here for a good while, but nowhere near what Ivan was.

As for the line, make sure you got it all off. It sounds like there's still something wound up somewhere and you're out of balance. 50lb won't usually do damage to a screw on a boat like yours; my money is on there being something out of balance.

[solanderi]

For clarification,

That does not sound like a DIY project, does it? Does that mean take the boat out at the yard and have the running gear evaluated?

Will a vibration damage the tranny, shaft, stuffing box etc? In other words do I cancel the weekend fishing trip? Thank you

[Genesis]

You can tear up your gearbox and do other similarly expensive kinds of damage this way, yes.

I would not run the boat until you figure out what is going on.

[Nonchalant1]

If you noted the vibration durnig an engine room check, that means you see the vibration at the forward end of the shaft?? That's probably not caused by line at the prop end. However, 50 lb line is small enough to get stuck in between the shaft and the water lubricated cutlass bearings by getting wrapped up on the shaft. It can then keep water from lubricating the bearings, which are usually a kind of hard rubber-like substance.

Either way, haul it and check out all the running gear. (ouch)

Doug Shuman

[solanderi]

How exactly is this problem evaluated ? Does any boat yard offer this service or do they need special equipment ? I am in Miami. The line that I cut away was wound up over the prop wheel itself and then tightly at the upstream side where the shaft and prop join. (ie the inside of the prop collar). Isn't the cutlass bearing in the strut? Thank you for any assistance

[Nonchalant1]

Yes, there's a cutlass bearing in each prop strut, including the last one right at the prop. If the line was all aft of that, I can't imagine how the line hurt anything unless it kept water from exiting the last bearing.

Many marinas can handle this type of issue. Likely people here can tell you whom in Miami area does good running gear alignment work, or if not, just look up a few, call around and pick one.

If the answer to the question about if you saw the vibration at the engine end of the shaft is yes, first try taping a pointed stick to a strut on the engine room floor with the point 1/4 inch away from the shaft. Then have somebody else run the boat at idle while you watch the shaft vs. the end of the stick. If the shaft wobbles, you'll see it easily. Then try the same thing at 1200 RPM, because running gear kind of self aligns when working. Again, note if there's much wobble evident at the shaft. You may find that it's the packing gland that wobbles, which they sometimes do, and the shaft itself is running true. If the shaft wobbles, then show that to the marina you select. They'll send somebody out with you to see what you saw so they can evaluate it. They do have special equipment, but usually somebody that knows what they're doing can do the primary cause evaluation by hand and eye.

If it's something like an engine mount that gave out, maybe they can do it in the water. If it's a wobbling gland, maybe the weekend fishing trip can still happen. If it's shafts - props - bearings, they'll haul it and it usually becomes apparent upon inspection by a knowledgable person and can be fixed there at the marina. If it's very minor, maybe they'll tell you not to worry about it unless it gets worse. If it really is significant shaft vibration, you need to get it fixed right away.

My 53MY had vibration when I bought it. When it was hauled, I taped a pointed stick to the rudders with the point exactly at the center hole in the end of each prop shaft, about 1/4 inch away. When I turned the props by hand, the sb shaft showed wobble compared to the stick. I got a marina tech and he verified it and did the work. That shaft couldn't be straightened so I spent $800 for a new stub shaft and also got new cutlass bearings on both shafts and alignment of both shafts. Now it doesn't vibrate (until I hit the next thing or run shallow ).

Stuff happens, and you get it fixed. It's good that you noticed it.

Good luck and let us know how it goes,

Doug Shuman

[Fanfare]

A 50 lb. line can't hurt your shaft bearings or alignment. There is so much bearing surface that would have to be worn away that even a really strong line would break or be worn away before doing any damage. Ignore it for 10 running hours and see what happens. If the shaft is truly bent, the packing gland will begin to leak--which looks bad, but really does not let in much water and can be tightened at the end of the day.

Things DO happen that can disrupt the shaft-bearing-stuffing box and they can be hard to diagnose. Your wobble was probably there all along, but you never had reason to look closely before, so now it looks bad. It's easy to spend a lot of money checking these things out when there is usually nothing there. It takes something over 150,000 lbs. force to bend a 2" shaft, which a rock can do, but not fishing line. I'm betting you are OK. That's because I've "been there, done that."

Good luck!

Jim Grove (Fanfare)