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Old 02-19-2017, 02:29 PM   #1
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Hit Something--how much vibration is tollerable

We recently hit an underwater obstacle at 8 knts, producing a distinct thump, thump sound. No grinding or other noise, just thump, thump. I checked in the wake and nothing appeared. Now at 8 knts there might be an almost indistinct vibration yet a sensation for sure. However, at WOT (12 knts) a modest vibration is apparent. I have a few questions:

My routine haulout is still a year and a half off. If I continue my routine of boating (100 hrs a year, at avg 8 knts) will permanent damage occur of any kind? At cutlass?

Key question: Can I hold off on prop repair for another year and half till time for paint, zincs, etc? Need input to offset the Admiral's fears.

If you have experience, is the damage from the hit as described likely to be on two blades of one prop or one blade on two props. As I said, the hit was a distinct thump, thump, with almost no delay between them. We clearly didn't hit a rock.

Assuming prop damage, would it likely be a slight cupping, or as bad as a tear of some kind. As I said, the hit seemly distinct, but relatively soft.

I'm intested in your thoughts before finding/sending a diver down in very murky CA Delta waters at $200 or $500 for a quick lift and inspection.
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Old 02-19-2017, 02:41 PM   #2
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Probably won't hurt it to run as is if vibe is minimally noticeable. Probably hit only one prop, but still a good idea to have both serviced as a pair to get them identical.
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Old 02-19-2017, 03:07 PM   #3
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You can't tell until you look. You might as well haul her because if a diver finds anything you will have to do that anyway.

Do you have insurance?
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Old 02-19-2017, 03:13 PM   #4
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Have insurance and notified the company of the incident but with $1,400 deductable, not sure I'll be filing a claim.
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Old 02-19-2017, 03:18 PM   #5
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Know any divers? I would get someone under the boat and take pictures. Then you know what you are dealing with.
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Old 02-19-2017, 03:21 PM   #6
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Greetings,
Mr. CO. As suggested, probably worth having her hauled and checked out. Probably prop but might be shaft or....
Vibration in the stern is not usually a good thing....

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Old 02-19-2017, 03:22 PM   #7
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Quote:
Originally Posted by rt firefly View Post
greetings,
mr. Co. As suggested, probably worth having her hauled and checked out. Probably prop but might be shaft or....
Vibration in the stern is not usually a good thing....

lol!
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Old 02-19-2017, 03:55 PM   #8
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I'd want to know what it is before I used the boat another year and a half assuming it was ok. If you can't jump in for a look it might be worth a lot of sleep to hire a diver to check it out and also maybe snap some pics.

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Old 02-19-2017, 04:00 PM   #9
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Ted, I had a similar event years ago. Nothing in sight in the water, but I definitely hit something. I presumed it was a submerged log. I had a noticeable vibe on the port side which was most prominent when standing in the salon over the shafts.

Paid a diver to pull both props. The tweak on the port prop was barely visible and easily overlooked. I doubt a diver could have seen it in murky water. I took them for a Prop Scan in Sacramento at Thomas Marine Propeller. Steve Thomas did a great job and now both prop profiles reside in his computer so if another gets dinged, I'll only need to pull the one to get it returned to normal. The next week the diver returned to install the props.

BTW, I gained a fraction of a knot at WOT and the end result was much smoother than before the hit.
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Old 02-19-2017, 04:02 PM   #10
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Even a camera could give you an idea. With a GoPro you could probably take a picture. Still I'd send a diver for a look. I'd do it with you there so he can describe and pull the props if you want him to. Have them take photos. Also, he should be able to advise if from the nature of the damage he'd recommend hauling and checking the shafts.
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Old 02-19-2017, 04:42 PM   #11
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If it was my boat I would haul and have both props checked. You could have a bent strut too. Doubt if a diver could see it in murky water. You would be surprised how much damage could occur and still only have minor vibration.
Also set up with yard and prop shop to minimize time out of the water so you don't also need a bottom paint job too
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Old 02-19-2017, 05:01 PM   #12
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So true...

Sometimes the visible damage is small compared to the amount of vibration...

And sometimes the other way around....

Experience is the key to letting it slide or not.

If you can't tell, and can't get a trustworthy advisor to help...then best to pull or let sit...both are options if you let them be.
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Old 02-19-2017, 05:11 PM   #13
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Caution in me says take a look, even if it is just a reassuring quick haulout on the straps. If you have bent something it can have knock on effects, so play safe.
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Old 02-19-2017, 05:47 PM   #14
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What is external arrgt?
Can you turn the shaft (s) by hand from inside? If you can turn it is unlikely to be anything significantly bent.
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Old 02-19-2017, 05:50 PM   #15
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Hit wrong button and cant edit!
If you can turn shaft easily...
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Old 02-19-2017, 05:52 PM   #16
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Propeller damage only giving small vibration doesnt warrant urgent action.
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Old 02-19-2017, 05:56 PM   #17
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If it was my boat/my money, I would get her hauled, do the prop scan and ensure nothing else suffered. Properly tuned props reward you with greater efficiency, you don't risk making problems worse (dinged prop could result in premature wear on cutlass bearing) and you get peace of mind.
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Old 02-19-2017, 06:09 PM   #18
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Of course checking is the best thing to do if you are somewhere this can be done. I wouldnt waste time / money with a diver given your description.
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Old 02-19-2017, 06:17 PM   #19
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I'd jump in and have a quick look. It may be a short bit of rope wrapped around the prop and thumping against the hull. It could be sorted out in a minute or two at zero cost.
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Old 02-19-2017, 06:44 PM   #20
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Such as I would do... Some of this was mentioned, some not:

1. Can you turn both shafts by hand?

2. Even if you can or can't - Go out and run on first one then the other engine to try determine which gives vibration.

3. Once you become more sure which prop was hit... get good u/w flashlight and dive under boat to view and feel both props, struts etc. Also, wiggle each shaft in cutlass bearing to feel if either is too loose. It's OK to have very small fraction of play.

4. If you feel pretty darn sure which is the damaged prop... get it removed, trued, and replaced.

Good luck!! - Art
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