Keel Bolts

[salamicollie]

Looking to buy a iron ballasted fin keeler where the survey has pointed out the bolts are twenty years old and need inspecting - choices are to extract the studs (if they will), x ray or drop the keel and re bed. This of course being a boat has the front pair of bolts under the keel stepped mast....

Anyone had any experience of having keel bolts x-rayed and the likely cost - I have the horrible feeling it may be cheaper to have the yard sweat away and extract a pair to see the state they are in.

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[poter]

What boat is it?

poter

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[salamicollie]

Omega 34 - a Ron Holland design, Iron ballast fin attached to a GRP stub with 8 keel bolts

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[Sunnyseeker]

No X ray experience, but I had to have a bolt extracted on a Bavaria 390, iron keel, as there was quite a bit of rust around the bolts,
It didn't prove much apart from one bolt was good so surveyor and insurance happy...
The cost of the inspection was taken off the price of the boat, as the owner would face this question on every potential sale.
I think its down to the seller to prove the bolts are good or reduce the price?

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[poter]

similar to my Moody except you have a keel steped mast.

I had removed what bolts I could on my keel last winter and they were fine I did have a little movement on the keel against the stub, which you could see around the joint. Resealed & replaced the bolts no problem. the two that could not be got at were as tight as you could get them with a pair of 18 stilsons so not too worried.
If you have no movement after 20 years IMHO I would say leave well enough alone, unless you have some staining around the joint.

It will cost for xray, also depending on how accessable the bolt positions are, as much as £80 each shot, [quoted to me a year ago] so not cheap.
I believe, though not checked, that there is a mobile outfit now in the south west, maybe another forumite can help.

poter


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[Rick]

Here in Brisbane Australia, II know one of the better surbveyors recommends that bolts are checked with an ultra-sound - ETRS apparently perform this service, and the equipment will tell how long the bolt is, what the diameter is, and what condition it is throughout it's length - I was told about $250 to perform the test on all bolts in a 30 foot fin keel boat.

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[William_H]

From my experience with Non-Destructive Testing in aviation x-ray is generally grossly overated. To give you an idea x-ray is a source of x-ray passing through the job and landing on a photographic plate. The shadows of the different x-ray density of the materials it passes through give a picture. You would be relying on the density of the corrosion being less than that of the bolt and you should be able to measure the dimensions of the bolt from the shadow. Thats fine except that the rays may have to go through the hull (not a problem) but also part of the keel. so a side shot would go from one side through the bolt and keel while a vertical shot would pass from inside the hull through to head of the bolt. If the bolt was wasted you might only see the shadow of the good part of the bolt. X-ray is regarded as about 5% sensitivity. That means it takes a 5% or more change to show a change of shadow for the total material the ray passes through. This could easily be lost in the total material it passes through. So it is possible but there are many pitfalls. Draw yourself a diagram of what the ray has to pass through and you will begin to see the problems. In aviation you would have to prove the method by having a known degree of corrosion on the bolt then x-ray to measure the performance of the test. As has been pointed out there are better NDT methods like ukltrasonics but even that is not usefull if you just go looking, you need to have proven the method on an identical boat and keel and use the same coupling and test direction. If you are driven by insurance company to X-ray then it doesn't matter if it is not usefull if it satisfies them. If you really want them tested go to an NDT expert who is familiar and capable with all the methods and let him choose the best. I would however suggest either pull some bolts for examination or would it be impractical to add some more bolts to give you more confidence. If you go x-ray I hope this will give you some guidance to ask inteligent questions. regards will

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