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Old 01-08-2011, 08:19   #1
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How to 'Sound Out' a Hull . . .

... Some folks have advised tapping (gently) the hulls of both fibreglass and wood boats for "soft spots" or hollow sounding spots. As a novice to construction materials and techniques, I have been trying this tapping system on various boats I have looked at over the last few weeks, and the problem for me is that even good hulls give off different pitched sounds when you tap them, depending on what part of the hull you are hiting.

For instance, on a glass boat with a heavy keel as you tap down toward the keel, the pitch of the sound gets higher and sounds more like a "crack" than a "thump" (low pitched sound). Obviously that is because that part of the boat is very "solid" with some kind of heavy reinforcement behind the glass, so that the keel can be attached.

However, as you move up the hull toward the water line and deck, the sound will change and even sound "hollow" at times. As you move forward or aft, the sound will also change from more like a "crack" to a hollow sounding "thump", apparantly because where one hears the "thump", one is tapping at the center point between reinforced elements of the hull's structure. When one hears the crack, one is tapping on a reinforced section of the hull.

All this being said, how can one tell much from the sound of tapping the hull?

Any advice would be appreciated.

Regards to all,
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Old 01-08-2011, 08:33   #2
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Re: How to "Sound Out" a Hull ...

Nothing magic about it. The only thing you lack is experience in sounding hulls which can easily be gained by doing it repeatedly and examining the structure around which the various sounds appear. A plastic aka phenolic hammer is the preferred tool .
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Old 01-08-2011, 08:44   #3
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Re: How to "Sound Out" a Hull . . .

You have to remember that the hull is not equal in all areas so the sound will differ. First off, use a ball peen hammer or something similar so that you have a good "bell clapper."
- - Thicker areas will sound different than thinner areas and even thinner areas with bulkheads or stringers behind will sound different. This is a good way to also find out where the bulkheads and stringers are located so you can position jackstands there and avoid "oil-canning" the hull.
- - Voids and blister in the laminate will really sound different than the surrounding good hull/laminate and as sv Illusion states you simply need to get more experience listening by tapping more boats. If you can find a boat with a blister laminate problem and tap it you will notice immediately the difference in the sound.
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Old 01-08-2011, 09:06   #4
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Re: How to "Sound Out" a Hull . . .

From 2008
Hammer-Sounding a Hull (Tap-Test):

The methodical process of Tap-Testing or Hammer-Sounding a hull leaves a lot of room for interpretation, which only comes with experience.

While the layman may not to be able to interpret the exact tonal qualities returned, you should be listening for any sudden, unexplained (bulkhead, stringer, etc) change in sound.

Lightly tap the hull with a clean*, lightweight (4 oz?) plastic (or rubber) hammer, hitting the hull squarely (to avoid leaving marks). Generally, begin your tapping in a visually “good” location, higher on the hull. This should give you a baseline reference.

* I wrap the hammer head in a clean cotton scrap of rag (secure /w elastic hair band)

As the hammer strikes the fiberglass hull, a clear, crisp report should be heard.
Good, dry, solid laminates give a clear, crisp, higher pitched return (ring), and the hammer will be lively, springing back with each tap.

If the report is dull or dead, and sounds like a watermelon, there may cored material that is wet.

Cored hulls return less ring, and wet laminates gives an even lower dead tone (thud).
Bulkheads, stringers, and grid liners also return lower dead tones, somewhat like a slight echo or drum sound.

Place your fingertips near the strike location, feeling for a sharp crisp vibration (tingling).
Your eyes should also be focussed on this area, looking for blemishes, disturbances, discolourations, etc.

More ➥ Need Some Advice on Hull Inspection

Although directed to surveying wooden hulls, the following offers excellent advice, also applicable to ‘glass hulls:
Surveying Wooden Boats: It's More Art Than Science
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Old 01-08-2011, 09:09   #5
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Thanks to both you guys ...

Quote:
Originally Posted by osirissail View Post
You have to remember that the hull is not equal in all areas so the sound will differ. First off, use a ball peen hammer or something similar so that you have a good "bell clapper."
- - Thicker areas will sound different than thinner areas and even thinner areas with bulkheads or stringers behind will sound different. This is a good way to also find out where the bulkheads and stringers are located so you can position jackstands there and avoid "oil-canning" the hull.
- - Voids and blister in the laminate will really sound different than the surrounding good hull/laminate and as sv Illusion states you simply need to get more experience listening by tapping more boats. If you can find a boat with a blister laminate problem and tap it you will notice immediately the difference in the sound.
... and, Osirissail, now that you mention it, I have seen a boat with bad blisters once. They were big enough that they didn't need to be tapped to let you know the hull was in bad shape. Looked like you could put a pin through them.

So, is looking at the line of a fibreglass hull a good indicator. If the side of the hull looks smooth and uniform, most likely its good, no?

Thanks again,

G2L
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Old 01-08-2011, 09:12   #6
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Re: How to "Sound Out" a Hull . . .

Gone2long,

Many years ago, a fiberglass boat builder/surveyor, suggested to me that pinching a quarter between a thumb and finger to use its edge to sound a glass hull is a good alternative to a plastic hammer. The tone between delamination and undamaged glass is readily heard. And sounding the boat is physically easier on overhead and vertical surfaces, because the quarter is much lighter. A bit handier too when crawling on hands and knees. You can cover a lot of area very quickly.

The previous suggestions to compare the sounds of known delamination against undamaged plastic will be worthwhile so you can readily recognize the differences. I have found that the tonal quality between "good" and "bad", is readily recognizable, despite "thick" and "thin" glass.

Roger
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Old 01-08-2011, 09:35   #7
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Re: Thanks to both you guys ...

Quote:
Originally Posted by Gone2long View Post
. . . So, is looking at the line of a fibreglass hull a good indicator. If the side of the hull looks smooth and uniform, most likely its good, no?
Thanks again, G2L
Yes and No. The obvious blisters will show up as domed areas but also the area might be a hull repair that was not fared very well. But with visually spotting suspect blisters/delamination then tapping the area you can get a quite good idea of the hull. And if there are obvious visual blisters there can also be hidden delamination due to osmosis that is not yet visible but can be detected by tapping.
- - Again we are talking about hull integrity which can be compromised by laminate blisters or rotten metal plates. Cosmetic gel-coat blisters are not a structural problem, but could be used to bargain the price down some since they need to be peeled or ground out and filled.
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Old 01-08-2011, 09:45   #8
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Re: How to "Sound Out" a Hull . . .

Thanks again to all for the tips.

G2L
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Old 01-08-2011, 09:51   #9
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Re: How to "Sound Out" a Hull . . .

I use a plastic very small ball-peen. It is universally known as my "money hammer", because it finds us lots of work. The advantage to a very small ball-peen is that the head is actually small enough to open up tiny voids, usually in radii. Look for a hammer with "bounce". It's not just sound, how the hammer feels and bounces is important too.
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Old 01-08-2011, 09:55   #10
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Re: How to "Sound Out" a Hull . . .

You are right...different sounds everywhere. I think it's more of a comparative thing... for instance, foredecks are infamous for getting wet cores. Try tapping all around the foredeck, (it will sound different where bulkheads are and around fittings etc,) however, if on one side it sounds a little dead...try the "mirror image" on the other side...does it sound differnt? When you tap the hull between bulkheads... do you get one area that seems rather dull sounding? It's an art for sure... Unless it's a cored hull, not sure you need to do much tapping on the hull....
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Old 01-08-2011, 10:02   #11
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Re: How to "Sound Out" a Hull . . .

Quote:
Originally Posted by Cheechako View Post
You are right...different sounds everywhere. I think it's more of a comparative thing... for instance, foredecks are infamous for getting wet cores. Try tapping all around the foredeck, (it will sound different where bulkheads are and around fittings etc,) however, if on one side it sounds a little dead...try the "mirror image" on the other side...does it sound differnt? When you tap the hull between bulkheads... do you get one area that seems rather dull sounding? It's an art for sure... Unless it's a cored hull, not sure you need to do much tapping on the hull....
One taps out a solid hull to find delams. A heavy impact can leave no obvious exterior damage but a severe delam in the hull. And of course voids are possible anywhere...
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Old 01-08-2011, 17:10   #12
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Re: How to 'Sound Out' a Hull . . .

HEre's a thought:

If you hang around boatyards much, you will eventually encounter a surveyor doing his tappy tap thing. If approached properly, he might let you sticky-beak along with him, and let you hear what a bad spot sounds like. I've done this and found it very educational. Sometimes a cold beer helps improve the surveyor's attitude...

It is a very useful technique to learn, so good luck.

Cheers,

Jim
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