Latest News: Forums Technical Centerboard bolts: How tight is too tight?

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  • #4484

    Hi all,

    I have just discovered why my Mk-II slowly fills with water when sailing. Upon removing the floor boards I found that the nut on the centerboard bolt had worked lose allowing water ingress by not holding the rubber seals firmly in place. Obviously it needs to be tightened up but I was wondering can you over tighten it and damage the boat?

    I also think I will add a locking nut to prevent it working loose again.

    Any comment welcome.




    I tighten mine quite tight (Mk1 wooden boat), the idea being that the centreboard rotates around the bolt and that the bolt does not rotate with the board. There are various rubber seals that are used, including Grolsch bottle seals. I have made my own seal with a 10mm rubber O ring and a 4mm rubber gasket fitted under a 30mm dia stainless washer & nyloc nut. It cured my annoying leak in that location.


    Hi, On my GRP dinghy as well as the rubber seal I also used some Sikaflex between the GRP and washer as the surface isn’t as even as wood and as a result have no leaks, Keith.


    True, the board turns around the bolt and the bolt does not need to move but a tight bolt will pull the sides of the CB case together making them act like a break. At some point a tight bolt may prevent movement of the CB all together. That is why I prefer this solution:

    1. Get some round 25 mm POM rod (also known as Delrin).
    2. Cut off a piece that is 1 mm longer then the width of your board.
    3. Then dril a 30 mm hole in the board and fill it with a mixture of epoxy and glass bubbles.
    4. After the epoxy has set, plane the board and drill a 25 mm hole in it to fit the POM piece.
      You now have a 2 mm layer of glass/epoxy inside the hole to protecting the wood from the water.
    5. Drill a hole in the centre of the POM piece to match your CB bolt.
    6. Fit the board with the POM piece inserted and tighten the bold to your harts content.

    Because the POM piece is wider then the board you can’t jam the board and there will be enough pressure on the rubber washers to ensure a tight seal. Pictures !

    As for the washer to use, look here. If not the best, at least it is the most fun solution.
    The suggested Sikaflex solution is a bit messy if you have to remove the bolt again at the end of the season.
    Consider using two rubber washers on each side instead or plane your CB case with some epoxy filler in the area where the bolt sits.


    Thanks for the suggestions

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