Hit Something--how much vibration is tollerable

[Hawkeye]

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.

 

[Ski in NC]

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.

 

[Xsbank]

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?

 

[Hawkeye]

Have insurance and notified the company of the incident but with $1,400 deductable, not sure I'll be filing a claim.

 

[wwestman]

Know any divers? I would get someone under the boat and take pictures. Then you know what you are dealing with.

 

[RT Firefly]

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....

 

[Lou_tribal]

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!

 

[kchace]

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.

Ken

 

[FlyWright]

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.

 

[BandB]

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.

 

[High Wire]

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

 

[psneeld]

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.

 

[BruceK]

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.

 

[stone beach]

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.

 

[stone beach]

Hit wrong button and cant edit!
If you can turn shaft easily...

 

[stone beach]

Propeller damage only giving small vibration doesnt warrant urgent action.

 

[Recb]

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.

 

[stone beach]

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.

 

[AusCan]

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.

 

[Art]

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

 

[Giggitoni]

Have insurance and notified the company of the incident but with $1,400 deductable, not sure I'll be filing a claim.

Shoot, it'll cost you $1,400 for all these opinions! My vote is to pull it and move your scheduled maintenance up a bit.

 

[Northern Spy]

GoPro on a stick or borescope inspection (Like a Rigid seesnake) would be my first check.

 

[BlindHog]

Go to the local boatyard and see if they will just lift you out to check for $100 cash. Saturday's are usually best time for this to occur. . I would check ASAP to be sure. Vibrations, even small can lead to larger problems.

 

[tadhana]

If the object you hit was hard, you may feel a nick on a blade or see a curled leading edge. But even a soft grounding can bend a blade so sightly that you cannot see the damage by eye, but the prop scan will show you why you have the vibrations! We hit a huge transparent plastic bag which brought the boat from 8kt to 3. Backing and filling we got most of it off. Had a vibration. Was hauled and there was a large amount of plastic still on the prop. Took it all off and sea trialed the boat. Still vibrating. Haul the boat a second time. No visible damage to the naked eye but we could find a bent blade with a measuring stick clamped to the rudder. So we took the prop to a prop shop. Indeed one blade was twisted out of pitch, but two blades were out of Rake. This is damage that you are not going to see in the water. So my recommendation is to haul the boat and recondition both props.

 

[Dougcole]

I went aground on a trip up the gulf coast a few years back and bent all four prop blades pretty badly on both props. A couple of them were even rolled a little. Amazingly, they really didn't vibrate that much and we only lost about a knot or so.

After I had them pulled I was surprised at how bad they were.

 

[DHeckrotte]

Go down into the ER at various speeds, cruising, and at WOT. Put your hand on various places THAT AREN'T TURNING and get a sense of vibration and which engine. Then decide to ignore or pull.

(Our marina does a dirty bottom special since Swan Creek is the proverbial primordial soup. Not a lot of money for a quick pull and a clean bottom. And, there's a fine prop shop a few minutes away.)

Better, I think, to err in the direction of spending some boat dollars now rather than more later.

 

[BandB]

The initial question was ""how much vibration is tolerable" (spelling corrected).

Answer:

None if you don't know what the nature of it and cause is. It could be many things and props are only one. You could have loose engine mounts, bent shaft. You could just have something wrapped around your prop and if it's removed before usage escape damage, but, if not, exacerbate the potential damage. It could be internal to an engine.

So, None is tolerable.

 

[psneeld]

Seriously..

Is damage the issue or vibration?

Having run boats with some damage and little vibration is no big deal under light use.

Vibration is annoying and can be damaging over the long haul but hard to put numbers on.

None is a good answer but not the only one....especially if the boat is run far less than max in all parameters....and monitored for obvious things and deterioration.

As I posted before....experience would be the key, if you don't have it, seek it.

 

[Northern Spy]

Actually vibration may or may not be tolerated, and it is actually quite easy to measure with the right (expensive) analyzer. ISO is the keeper of vibration standards for balance and vibration. I would venture a guess that most inboard boats wouldn't even make a satisfactory grade for medium machines and most props wouldn't make an ISO G16 balance.

That said, I've not heard of anyone completing vibration analysis of a recreational boat. I'm sure there there is a market on the higher end that I haven't encountered. I think there could be lots of room for improvement, but the need isn't there or the market doesn't demand it, or want to pay for it.

I'd go easiest to hardest, cheapest to more expensive on any troubleshooting.

 

[dhays]

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....

I'm beginning to think that RT finds these gifs, then cons another TF member to start an appropriate thread so he can use them.