Building bomb-proof cleats/strong points.

Discussion in 'Fiberglass and Composite Boat Building' started by elhix, Dec 20, 2009.

  1. elhix
    Joined: Feb 2005
    Posts: 14
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    Location: UK

    elhix Junior Member

    Hello,

    I'm finishing the four year build of a 32 foot cat that will be sailed offshore. I want to be sure I have attachment points on the bows and sterns - for para-anchors and drogues respectively - that I can have absolute faith in.

    Any opinions on the construction of indestructible strong points?


    The boat is foam sandwich construction, the basic hull laminate is 800gsm biax/15mm foam/800gsm biax.

    Cheers All!
     
  2. Submarine Tom

    Submarine Tom Previous Member

    Through bolting and thin, graduated backing plates.

    It comes down to a "weakest link in the chain" scenario.

    I don't have the expertise to comment any further I'm afraid.

    This is a challenge to be sure.

    -Tom
     
  3. mark775

    mark775 Guest

    Tom, just so I don't step on your intent - What do you mean by "thin, graduated backing plates" and why?
     
  4. Submarine Tom

    Submarine Tom Previous Member

    Good question., thank you.

    Graduated thickness, stepped to spread the load.

    Does that make sense?

    -Tom
     
  5. Submarine Tom

    Submarine Tom Previous Member

    Like a relief map of a mountain.

    I wish I could put up a graphic.
     
  6. mark775

    mark775 Guest

    I thot that was what you meant. I have tried what you say to spread out the loads on backing plates, I've experimented with a bit of a "sprung" backing plate to spread the forces. What it always seems to come down to is (as I think Par said) "Big Assed backing plates. What I have come up with is in line with what you are saying tho. First, mark where you are going to drill holes FROM ABOVE. Next, lay something tough (two or three plys of 24oz BTI would work nice) in a large area under the deck (okay, mark where they are going to go, lightly wet out the area, go off the boat, cut out the pieces of glass each a little bigger, wet out layers on cardboard one on top of the other, biggest piece last, and squeegee fairly dry but not distorted/pulled apart, pull off cardboard and hang there for a second, if it looks like it is going to drip, lay it on a dry piece of carboard to get rid of a little resin, gently fold if too big, carry on to boat on large, clean cardboard, place and roll with foam roller. I finish the edges with pre-cut three inch veil tape to keep the edges down), drill oversize holes making sure that they will be covered completely by your cleat, winch, puller, whatever - but only through the top skin and core. Then, coat core with epoxy, thicken epoxy and fill holes, let dry, drill for bolts a bit (pun!) oversize, test fit everything to make sure backing plate holes line up with mounted object and thru-deck holes, then take apart and 5200 everything in place, paying particular attention to the bolt shafts and spreading the load on the backing plate. Clean up 5200 with denatured alcohol. Does that sound reasonable? Same effect as the relief map, preventing the surface from flexing and having an edge dig into soft core material. Remenber the "Big Assed" part. A too thin or too small plate does little.
     
  7. Submarine Tom

    Submarine Tom Previous Member

    775, agreed.

    I was thinking about this situation this evening. During construction,

    anchor points (strong points) should have been layed in.

    Looped stranded wire could have been uncoiled and layed in over a VERY

    large area around the bow and stern. The exposed loops could then be used

    as strong points.

    Obviously, the key here is to distribute the load which is difficult to do after

    completion.

    I think there are a number of ways to do it, none of them easy.

    -Tom
     
  8. elhix
    Joined: Feb 2005
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    Location: UK

    elhix Junior Member

    Thanks folks,

    Just to clarify: I have prepared the ground during construction by removing the core in the way of all 'hard-points' and replacing it with either ply - in the case of the bow cleats - or thickened resin mixes in the case of stanchions, snatch-blocks etc. Whilst the majority of the boat is faired and hi-build painted the bows and sterns are still bare glass so further reinforcement is not a problem.

    Thanks Mark775: what you describe is what I sort of had in mind but thanks for laying it out clearly.

    Regarding using wires within the laminate (Submarine Tom), wouldn't radiating uni-directional glass or carbon work better with the resin?

    It'd be good to see a comprehensive study of attachment points in differently constructed boats and under different demands. Stories of cleats ripping out are not hard to find.
     
  9. Submarine Tom

    Submarine Tom Previous Member

    I have no idea, not my area of expertise.

    You probably have a better knowledge of it than I do.

    How can you distribute the load?

    In theory, you should be able to lift the boat off the ground by the two bow

    eye bolts...

    -Tom
     
  10. AndrewK
    Joined: Mar 2007
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    Location: Australia

    AndrewK Senior Member

    Elhix, I would be attaching the para anchor to the forebeam not cleats, this should have been glassed in to spread the loads well into the hulls already.
     
  11. Scrumble
    Joined: Aug 2008
    Posts: 27
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    Location: Darwin, Northern Territory, Australia

    Scrumble Oram 46'C MS Builder

    It is better to build all the blocking in first, reinforce the deck, placing a large backing plate
    which in the case (my boat) below is also threaded to act as the captive nuts for a para anchor chainplate with a 300mm Nomen cleat on top.

    http://scrumbleproject.wordpress.com/2008/11/16/forward-cleat-blocking/

    http://scrumbleproject.wordpress.com/2008/11/16/deck-reinforcement-for-cleat-mounting/

    http://scrumbleproject.wordpress.com/2008/11/17/forward-cleat-blocking-installation/

    One of these would take the boat weight in the horizontal plane.

    Suffice to say I have seen this sort of structure retrofitted where there is access in a compartment under the deck. If no access, you could just cut out the deck between stem and first bulkhead and start again!!
     
  12. elhix
    Joined: Feb 2005
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    Location: UK

    elhix Junior Member

    Tom,
    Thanks for a very informative and clear description. I've got easy access to the under-deck so the process would be much easier for me.

    Can I also congratulate on an incredibly clean job, you're even rather smartly dressed. Puts my resin encrusted overalls to shame...

    Thanks!
     
  13. TollyWally
    Joined: Mar 2005
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    Location: Fox Island

    TollyWally Senior Member

    I think the advice you've been given here is first rate. My only caveat would be that I only use 5200 for things I consider welded on, never to be removed. I use 4200 for things that might have to come off someday. Everything I do on my boat I do with the guy who is going to have to repair it in mind, cause that's going to be me! :) Just my .02.
     

  14. Scrumble
    Joined: Aug 2008
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    Location: Darwin, Northern Territory, Australia

    Scrumble Oram 46'C MS Builder

    Good points about 5200 and 4200.

    I personally would prefer to follow the guidance of The Goudeon Brothers on Boat Construction.and use an epoxy mix to bond as well as seal all hardware.
    The removal, in the future of epoxied hardware, is facilitated by using heating tools on the hardware to raise the boundary bond layer above its HD temperature - momentarily.
     
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