Supporting the rig

Discussion in 'Boat Design' started by Tiny, Mar 21, 2019.

  1. Tiny
    Joined: Jan 2009
    Posts: 10
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    Location: UK

    Tiny Junior Member

    I have a deck stepped masthead rig on a 10m yacht. Under the mast is a stainless post with a 200mm square flange, which ultimately bears onto a very heavy base of solid GRP moulded into the sump of the stub keel. Separating the base and the flange on the post is a spacer block of solid GRP, 43 mm thick. There are some coach bolts to locate it all laterally.

    As a result of the base not being quite flat (dished) originally, the GRP block has fractured and split right the way through, it being unsupported in the middle where the load is.

    I intend to grind the base flat, have straightened the flange on the post and welded gussets to the corners of the flange.

    The question is, what to replace the split spacer block with?

    I really don't have the patience to laminate a block of GRP 200mm square and 43mm thick!

    Given the location, it must be rot resistant. I could laminate over some iroko or similar to build the thickness quickly, or just get a block of acetal and build up the base the extra 3mm with mat, but looking at material strengths, these are only about a third to half the strength of what I'm replacing... and that cracked right through.

    What is the normal arrangement?

    Thanks in advance
     
  2. Blueknarr
    Joined: Aug 2017
    Posts: 526
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    Location: Colorado

    Blueknarr Senior Member

    Tiny

    If you have a marine services center near you; beg, borrow or steel some G10. It is fiber reinforced resin compressed into sheets. I have seen it as thin as .5mm and up to 2cm thick. It is quite expensive in full sheets but the size you need could come from someone else's scraps.

    Good luck
     
  3. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    This can be done quick and dirty. It doesn't have to be anything special. You don't have near the load I do and I built mine entirely from scrap I picked up of the ground in the boatyard where I was. Mine was 13" x 13" x 10", replacing 4 balks of rough hewn mahogany that had been bogged in with about a gallon of polyester resin at the factory forty years earlier. The mahogany was removed with a spoon and I chiseled the resin off. This was fun because it was 2 feet from the nearest access, and even that required pulling the blackwater tank and working though a 5" high gap. Epoxy coated plywood or any decent (seasoned) board material will work fine. Wood is easy to cut and try. I wouldn't bother doing anything to recontour the sump or the pole flange, just build a wood block to fit and coat it liberally with epoxy (A little bit of a taper helps a lot though). Set up a jack from hull to deck to gain about 1/4 inch of space, mix some really thick epoxy bog, place you block, then let the jack down to squeeze out some bog. Overdrill the lag holes, fill will with epoxy, let cure fully, then drill and tap. You can make a tap out of an extra lag screw.
     
  4. Tiny
    Joined: Jan 2009
    Posts: 10
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    Location: UK

    Tiny Junior Member

    Belated thanks. I opted for G10 in 10mm sheets which I laminated to the required thickness. Seems bomb-proof.
     
  5. Blueknarr
    Joined: Aug 2017
    Posts: 526
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    Location: Colorado

    Blueknarr Senior Member

    Bomb proof indeed.

    Were you able to obtain scraps or did you have to auction off a kidney?
     
  6. Tiny
    Joined: Jan 2009
    Posts: 10
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    Location: UK

    Tiny Junior Member

    Sold a kidney. Wrecked a new blade in the bandsaw too, which oddly justified the cost.
     

  7. bruceb
    Joined: Nov 2008
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    Location: atlanta,ga

    bruceb Senior Member

    Recycle!
    I can usually find a GRP boat that is being cut up, or at least some part of it. I try to keep some fairly flat hull section parts and some with a bit of a curve, most yards/scrapers are quite happy to let me have as much as I want since they have to pay disposal fees to get rid of it. One or two layers epoxied together make great backers, more layers can do many repair jobs at a very low cost. G-10 is great material, but the GRP hull parts used in compression is quite good also and almost free. I find blades made for fiber/cement materials last pretty well.
    B
     
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