Corrosion and keel bolts

[eranb2]

Hello,

I wanted to ask if there is any law about checking the bolts of keel on old boats (20-30 years).

Can corrosion attack the all bolts or just the weakest part of the keel (zinc) ?

I can't open the bolts in my boat (1987 jeanneau) , can I assume that if they were damaged by corrosion they would be just tear apart? they look like new.

last year the chain plates bolts (10 m"m) just broke like margarine because of corrosion, little power on them just broke them, so in the keel it should be the same right?

If the keel bolts are rotten then they should brake ???

How can I know that the upper part of the keel is not rutten , is there a way, without dismantle the keel apart?

I think that every fin keel owner should check the bolts every time on 3 years or on shipyard.

5 years ago while crossing the Atlantic ocean (with reliance) the skipper (after 19 crossings) told me that he always take a big hummer and beat the bolts, if they are rotten then they will fail, is that good way to check?


can electricity attack the bolts?
by the table in nigel calder book, what will fail first , the keel or the bolts? (electricity potential difference)


Thanks

 

[Tranona]

So many questions and so many answers!

Normally keel bolts in GRP boats are not a problem (although they can be in traditional wood boats). There are different designs, but usually either a stud screwed into the keel and then secured with a nut inside the boat, or just a bolt screwed into a thread cut in the keel. The stud or bolt is often stainless and the keel cast iron. Provided the seal between the keel and the hull is sound there is no problem with corrosion. It is only if the seal fails, for example in a severe grounding that water gets in and there is the potential for corrosion. The seal can also fail if the hull flexes where the keel joins and the seal breaks down. Signs of potential corrosion usually are related to rust stains on the join or sealer breaking away. Water mat also weep out when the boat is out of the water.

Alternatively if water is getting into the boat through a leaking keel bolt or seal it is obvious internally. Nuts or bolts can easily be checked for tightness (if the heads are not glassed over). Actual corrosion of the bolts can normally only be checked by withdrawing them, although it is possible to Xray, particularly useful for full length bolts in traditional construction.

Rarely do keel bolts fail. They are usually 20mm plus thick, more than 6 to a keel, so symptoms as described occur long before there is any likelihood of failure!. Does not remove the need for regular checking, though.

From your earlier posts it seems you are worried because your keel seems to move. If it really is moving in relation to the hull, the seal may break letting water in which may then corrode the bolts and the top of the keel. If the keel and the hull are flexing together then it is a different issue and failure may result from the grp failing. This is usually obvious internally with cracks showing in the GRP and any stiffening such as stringers or floors.

If you really are worried, engage a surveyor for his opinion and follow his recommendations.

 

[nct1]

There is not much written about keel bolts in the books you see at boat shows, but I have found the following.

Surveyors sometimes ask for you to pull one bolt per season for older boats, this is not a bad idea.

For my 1980's AWB I found that 2 people on a 6 foot T bar bracing against the interior could not shift my bolts (they are bolts not studs) but an impact drive designed for the removal of lorry wheel nuts will remove this (it has a one inch shank).

What I do not know is if I have re-tightened them up sufficiently but will find out in about a month's time /forums/images/graemlins/ooo.gif

All the best whatever you decide