Latest News: Forums Technical Sealing the centreboard bolt on a Mark 1

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  • #26216
    Alison Corfield

    I have recently refitted a centreboard into my old mark 1 and realised the bolt hole is below the waterline! How do I seal this?


    Hello Alison.


    If he was still with us I bet Swiebertje would have replied by now!

    Search on “centreboard bolt” and I am sure you will find a post all about Grolsch beer and in particular the rubber washer you will find under the cap, you might need to buy two bottles. These washers are just the right size to seal the bolt holes.

    If you are a bit handy with resin you could try the Danish Bush, search for the Wayfarer Institute of Technology and find “Everything about rudders and centreboards”.  If you decide to go for that I have some Delrin you can have, ping me a PM.


    To seal mine a few years ago, I used an exterior sealant when I was reinstalling the bolt.  I smeared plenty on the area of the hole and on the rubber washers (backed by stainless washers) bearing against the side of the centre-board case, then I tightened up the nut until the sealant was starting to ooze out from the sides of the washers.  Then I waited until the sealant was almost hardened and gave the nut another little tighten.  Fully tightening it too soon may squeeze out all of the sealant.

    The nut doesn’t need to be supertight. Just enough to ensure that the sealant is in full contact all around the hole.  If you over-tighten it,  you risk cracking the centre-board case.  Remember that the bolt is only there to act as a pivot for the board. As long as there’s a nut on the bolt, the bolt can’t fall out.

    Finally, to be sure to be sure,  I smeared just a little more sealant around the head of the bolt and nut after everything had dried.  Maybe a bit of overkill, but it hasn’t leaked since.


    Regards, davdor

    Alison Corfield

    Many thanks all – v helpful

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