mechanical fastenings through tabbing?

Discussion in 'Fiberglass and Composite Boat Building' started by robwilk37, Feb 24, 2016.

  1. robwilk37
    Joined: Nov 2010
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    robwilk37 Senior Member

    watch a video the other day about a guy re-fitting a 40'ish hinkley. upon re glassing the floors he made the comment that he'd driven wood screws through the tabbing just as the original builder did. wondering if this a common practice as i dont think ive ever seen it before other than what ive always considered to be a half-assed repair. my tabs are massive, 6-8 layers of 18oz biax in epoxy, 8" tape staggered 5" either side of the joint and i have high confidence in my work and the goo. what i dont trust is what passes for "marine grade doug fir ply" these days as i occasionally find delams when cutting up scrap pieces. not often but more than once and it could all have come from one sheet out of the 30 or so ive gone through, but still.

    so wondering if screwing/bolting through the tabs is worthwhile, overkill, causes more problems than it solves or what...

    tia


    and im thinking of bulkhead tabbing at this point as my new laminated floors are hat sectioned in uni and biax
     
    Last edited: Feb 24, 2016
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Screwing the tabbing is dubious at best. If your methods are well established and within the usual norms, you don't need mechanical fasteners.
     
  3. robwilk37
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    robwilk37 Senior Member

    my thought also. it was the statement that 'thats how hinkley does it' is what got my attention, as ive always been under the impression they are a top quality yard. wanted to make sure i wasnt missing something that is easy to do now, much harder later on in the build.
     
  4. FAST FRED
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    FAST FRED Senior Member

    "i have high confidence in my work and the goo.


    Polly goo is what most folks use to build hulls. Polly resin is NOT a glue.

    Take some scrap and see how easily it peals off wood.

    Epoxy IS a great glue , but the E goop is too expensive for most projects.

    Thru bolts with washers and nuts is required if the plywood will be caring a load of any sort.

    Especially a bulkhead that might have engine or rigging loads to it.
     
  5. rxcomposite
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    rxcomposite Senior Member

    In the early days when epoxy is still not available poly+glass is used for encapsulation, they staple the initial ply to the wood and then add the additional layer. Poly doesn't stick well to wood unlike epoxy, hence the need for "mechanical bond". With epoxy, there is no need as it grips the wood well.
     

  6. gonzo
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    gonzo Senior Member

    Considering the millions of successful boat built with polyester and plywood, I have to disagree. Epoxy is the new wonder substance, but there is no arguing with decades old boats that are still operating. It is a matter of designing the structure for the materials being used. The techniques and design for laminating with epoxy and polyester are different.
     
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