Pivot construction for catamaran kick-up rudders

Discussion in 'Multihulls' started by TomBlake, Jun 28, 2020.

  1. TomBlake
    Joined: Aug 2018
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    Location: Qld Australia

    TomBlake Junior Member

    I took my kick-up rudders into a boat builder. He cleaned and re-welded the rudder cassette and inserted resin into the holes and gave me the bolts and washers. After a quite abit of money he handed me back the pieces. Didn't drill a new hole and assembled the rudders, as he wanted more money for that.
    As advised, I then jotacote 605 to prime the cassettes and then undercoat with and then international perfection for final coat above water

    I fitted the rudders and drilled through the resin. Not happy as I broke off significant chunks of the resin when putting the bolt through.

    To cut a long story short, I'm thinking of re-doing the rudder where the bolts go through.
    Fitting stainless steel flanges on either side of hole and epoxying them in; after adding re-inforcement in that area as the pivot hole is close to the edge.
    Good idea? I would have thought the boat builder's solution was abit average and prone to failing in pretty quick time? Maybe there was a better way of drilling the holes. Builder did tell me to use a half inch drill bit

    From another thread i put up recently oldrudder.jpg , I'm probably going to make up another set of rudders.
     
  2. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Maybe drill a small hole first, and work up to the desired size, sharp bits, and water lubricated to minimize heat buildup.
    I’m sure you could find some flanged bushings to make a more durable insert.
    Grind a cupped area two or three times the diameter of the existing reinforcement and build it back up to spread the load over a larger area.
    Looks like there are already cracks radiating to the outside edge, just a matter of time before the whole thing lets go again.
    I’ve never had much longevity from wood cored kick up rudders, but sometimes it’s better to have a sacrificial item than to tear up the transom!
     
  3. TomBlake
    Joined: Aug 2018
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    Location: Qld Australia

    TomBlake Junior Member

    Yes there are a few cracks. Thinking of reinforcing that area with cloth and resin. I have some carbon cloth laying around?
    Probably should have spent the money in building new rudders
     
  4. TomBlake
    Joined: Aug 2018
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    Location: Qld Australia

    TomBlake Junior Member

    Should I put thickened resin back in the hole and start again?
     
  5. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    Its not hard to make a plug. Put some tape on the bottom side and pour or use a syringe to squeeze in silica and epoxy. Get it just above the surface, grind flat and start again. You can drill almost cured epoxy, when it is like hard rubber and it is less likely to shatter.

    Personally I have had no issue with wooden core rudders. Mine are 20 years old and like new. I do clean them down every couple of years and apply new glass to the bottom but there are multiple layers of double bias down on the bottom.
     
  6. aussiebushman
    Joined: Oct 2009
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    Location: Taralga NSW

    aussiebushman Innovator

    Yes, I'd remove the existing plugs, fill the holes with thickened epoxy and reinforce all round with glass cloth. As Phil says, drill new holes before the epoxy cures too hard Get some bushes made to be a precise fit into the new holes. These might be best in bronze - any decent fabricator can do this
     
  7. redreuben
    Joined: Jan 2009
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    Location: Beaconsfield Western Australia

    redreuben redreuben

    Drill the hole out.
    Slather the bolt with past wax and let dry.
    Wet out hole sides
    Make a filler paste with lots of milled fibre in it.
    Put a large washer on the pivot bolt and rap the pivot bolt with uni directional glass until size of the hole.
    Put some of your fibre paste around the inside of the hole, insert bolt and glass and another washer.
    Do up tight enough to squeeze out the surplus and let cure.
    Undo and tap out bolt, voila, one tough as waterproof pivot point.
     
    Corley likes this.
  8. TomBlake
    Joined: Aug 2018
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    Location: Qld Australia

    TomBlake Junior Member

    Great solution. Silly question. Do I soak the uni directional glass in resin as I wrap the bolt?
     
  9. redreuben
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    redreuben redreuben

    Wet it out yes, fibre is strong, resin is brittle.
     
  10. redreuben
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    redreuben redreuben

    And probably do all your other glass repairs around the area first.
     
  11. TomBlake
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    Location: Qld Australia

    TomBlake Junior Member

    Thanks. How much should I oversize the hole by??
     

  12. redreuben
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    Location: Beaconsfield Western Australia

    redreuben redreuben

    Geez mate, make that call sight unseen ?
    How about thickness of the bolt and double that at each end near the surface ?
     
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