Leaking forestay attachment

Discussion in 'Sailboats' started by Pammie, Apr 16, 2019.

  1. Pammie
    Joined: Dec 2015
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    Pammie Senior Member

    The chainplate of a boat I might want to buy has a leaking forestay chainplate.

    What could be the cause for this? An innocent cause could be different temp. coefficients, but there might be other reasons? What should I check?

    Another question is how to fix it. Normally one would expect the bolts to screw into locked nuts? Are there other construction methods used?
    So: Unscrew it. Remove chainplate. Clean. Put it back with PU kit. Put bolts back. ??
     

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  2. Angélique
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    Angélique aka Angel (only by name)

    Here's a thread about carbon fiber chainplates which looks like a definitive solution to the problem, but a lot of work to attach it to both sides on the outside of the bow, which also will lose its fair looks.

    For a more conventional repair of the current chainplate leakage I would lengthen the chainplate and the inside support plate way down to distribute the load over a larger area of the bow, this also requires adding new lower placed bolts and bolt holes.

    When it's off I would also replace the chainplate by a new one, since old stainless steel chainplates can spontaneously break by hidden crevice corrosion.

    P.S. - Maybe mount it all with Shell Tixophalte Wet permanent flexible bitumen kit, but check this first as I'm not sure, here's Dutch / English info.
     
    Last edited: Apr 18, 2019
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  3. Pammie
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    Pammie Senior Member

    Thanks Angelique.

    Ah, I didn't consider a CF chainplate. I know the article (used it as inspiration for the stay attachment on my catamaran). But indeed takes quite some work.
    The boat is 11 years old and in a harbour where maintenance might be difficult. So I'd better use the Tixophalte and rebed it. Will check for corrosion. Is this always visible?
     
  4. Angélique
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    Angélique aka Angel (only by name)

    Hi Pammie,

    Stainless steel crevice corrosion can occur in any crevice by taking away the protective effect of oxygen, which is to form an ultra-thin very effective protective closed oxide film on the marine class stainless steel surface.

    The crevice between the hull and the leaking chainplate can be filled with ultra aggressive deposits, which continuously break down the protective closed oxide film and keep the stainless steel out of reach of sufficient air and oxygen supply to form a good new protective layer, which is also broken down again by the aggressive deposits in the crevice, hence the stainless steel oxidizes with this continuously broken down protection without a good new build up. So these are the optimum conditions for crevice corrosion to occur, and this only in the crevice where it can't be seen as long as it's mounted, demounted it gives a chance for a close inspection and replacement if needed. Crevice corrosion that has already occurred can have caused notching in the chainplate which can lead to later breakage. Inspect also the bolts for the occurrence of crevice corrosion, since they did have to pass the aggressive crevice.

    So stainless steel needs to be in the free air for protection by oxygen, or it needs to be 100% closed off from any aggressive environment, which can be done by a good bedding in a permanent flexible kit and a strong and firm mounting. Also take care no water can ingress from under the bolt heads into the stainless steel holes around the bolts, so you'll need to fill the holes in the chainplate around the bolts with the same kind of kit to prevent this.

    Chainplate Maintenance, or the lack thereof . . .
    [​IMG]

    There's almost no info about crevice corrosion on the Dutch Wikipedia, so better look at the in post #2 linked English version.

    Dutch Wikipedia: CorrosieSpleetcorrosie

    Maybe I will later post some remarks about this Dutch thread: Wantputting inwatering en hoe dit op te lossen

    Good luck !
     
    Last edited: Apr 18, 2019
  5. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Difficult to tell from the small picture. But, since it is a bolted connection, it could simply be the bolts over time slowly wearing out their holes,;bearing stress.
    Or
    It could be occasional overloads and slowly pulling the plate and/or bolts and again, slowly elongating the holes in the plate or the structure it is attached too.

    Is it possible to get some water, colour it with red dye or similar and spray/pouring it over the region above..or better still create a simple dam around the joint above the deck...use putting/play doh anything. And then pour the dyed water into the well you created and leave it for say 1 day. See what happens....if you can apply a little pressure to it, even better :cool:

    Can you take the plate out at all??
     
  6. Angélique
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    Angélique aka Angel (only by name)

    Maybe diagonally cut a fire hose end and put it over the bow chainplate and duct tape it all around to the hull, then hoist the other end of the fire hose, with a thin hose in it to fill it from below, in the mast with the halyard, 10 m water height gives about 100 kPa (1 bar) of water pressure on the area around the chainplate. Which I think should be enough to see immediate effect down below. Now how to find about 10 m (or whatever the mast height is) of old discarded fire hose . . :)
    P.S.
    Note such ventures can take a long time before the fire hose hull joint is sufficiently closed, and this probably only to find out that it leaks around the bolts.
     
    Last edited: Apr 17, 2019
  7. rxcomposite
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    rxcomposite Senior Member

    FRP's tends to lose thickness under compression over a period of time. It is known as creep and highly loaded areas or off angle loads are checked every year and re tightened every 3 or 4 years. Retightening will initiate crack propagation and the succeeding cracks will extend the laminate yield point slope but not necessary fail the laminate. The cracks however will provide a path for water to seep in and hasten the expansion/contraction of the laminate voids.

    FRP is also poor in shear. So it is poor in compression and poor in shear. To mitigate this, metal compression bushings are used. It is just a little shy of the laminate original thickness such that when torquing, the allowable laminate compression load is achieved and the bushing just starts to deform(yield). Fender washers are used after the bolt head to disperse the top load. The metal bushing is strong in shear and takes the load of the FRP.

    For long term solution, the hole and the plate is coated with silicon adhesive sealant before assembly. The silicon adhesive/sealant have a much higher shear than the FRP.
     
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  8. Ad Hoc
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    Ad Hoc Naval Architect

    That'll do :D
     

  9. Pammie
    Joined: Dec 2015
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    Pammie Senior Member

    Well, I'm just orienting on the problems of this boat. What I heard so far is that I should take care of it but it is not a major issue.
     
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