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  1. #1
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    Default Adding a fitting to a cored GRP deck

    I apologise in advance if this is old hat but I am coming from fifty years of wooden boats. I am looking at my copy of Du Plessis, fifth edition, page 140:



    If I want to fit a windlass, on a pad, on the deck, held in place by four bolts, fitted as studs, with a pipe for the chain, with the heads of the bolts on penny washers on a marine ply backing pad, which is the best method to avoid compressing the core, whilst being as sure as I can that nothing is going to leak into the core? "A", "B" or "C"?
    Last edited by Minn; 16-08-19 at 20:56.

  2. #2
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    Default Re: Adding a fitting to a cored GRP deck

    Have a look at how WEST describe it in one of their manuals: 002-550 Fiberglass Boat Repair & Maintenance. Basically method C in your book but it is described in detail.

    https://www.westsystem.com/wp-conten...anual-2015.pdf

    See section 7.2.1 page 47
    Last edited by Poignard; 16-08-19 at 22:14.

  3. #3
    Join Date
    May 2001
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    14,371

    Default Re: Adding a fitting to a cored GRP deck

    I would go for 4, filling the scooped hole with resin putty and then drilling the holes for the bolts. BUT I would also put a large hardwood (or marine ply) backing pad on the inside surface of the deck to spread the load. If the windlass is of considerable size I would also add a stainless plate between the pad and the nuts instead of individual washers.
    Should we paint what is on a face, what is inside it, or what is behind it?

  4. #4
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    Sail on the Medway, Kent from Chatham Maritime Marina
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    Default Re: Adding a fitting to a cored GRP deck

    IIRC you have a Nich 43. I thought they either had a wooden deck or fiberglass side decks with a wooden coach roof. I very much doubt you have a cored deck. If there was anything as a core it would be plywood. You need to drill a hole to check. It will either be solid GRP or supported with plywood, in my opinion.
    If my foresight was as good as my hindsight, I would be a multi-millionaire.

  5. #5
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    Default Re: Adding a fitting to a cored GRP deck

    Quote Originally Posted by Concerto View Post
    IIRC you have a Nich 43. I thought they either had a wooden deck or fiberglass side decks with a wooden coach roof. I very much doubt you have a cored deck. If there was anything as a core it would be plywood. You need to drill a hole to check. It will either be solid GRP or supported with plywood, in my opinion.
    Nic 55, MOD version (Ray Wall calls these "MOD 55s") Some 55s (Lutine, Quailo III) were GRP with wood decks - those two have had complete new decks. Some (Pacha) were alloy with wood decks. The MOD 55s - those built direct to MOD order as opposed to bought in - were all GRP.

  6. #6
    Join Date
    Jun 2015
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    Tarbert
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    557

    Default Re: Adding a fitting to a cored GRP deck

    I have been sorting out my Nic 35, and the method that works is 1) drill oversize, 2) remove as much core as you can, 3) fill with epoxy and finally 4) drill the right sized hole. Done it for all the deck fittings on the port side of the boat and all the leaks are fixed. Just the starboard side to do now!

  7. #7
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    Default Re: Adding a fitting to a cored GRP deck

    Quote Originally Posted by adwuk View Post
    I have been sorting out my Nic 35, and the method that works is 1) drill oversize, 2) remove as much core as you can, 3) fill with epoxy and finally 4) drill the right sized hole. Done it for all the deck fittings on the port side of the boat and all the leaks are fixed. Just the starboard side to do now!
    Thanks. Just what I needed to know... what epoxy mixture do you use? (Incidentally have a deck leak over the port cockpit locker, which I think is down to a deck fitting...)

  8. #8
    Join Date
    Nov 2007
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    Boat Orwell - Me Norwich
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    Default Re: Adding a fitting to a cored GRP deck

    Epoxy mix - Standard resin & standard hardener, thoroughly mixed in the proportions recommended by the manufacturer. Then gradually add colloidal silica filler, e.g. West 406 (or other non-water absorbing load bearing filler) until it reaches a semi-liquid consistency which will slowly sag to fill the space it's put in. (More elsewhere in West manual (and no doubt vids) on thicknesses of fillers.)

    Follow the West Manual Poignard links to - 7.1.1 paras 1, 2, 3 and second half (only) of para 4. (I don't see the point in epoxying the fitting or backing plate to the deck unless there's a particular reason to do so.)

    I agree with Puff that something like Du Plessis diagram no. 4 is what you're aiming at. Very important that the point is to ensure not only that the deck is not crushed, but that any water leaking under the fitting (sealant should keep it out, but . . . ) goes into the boat interior, where you'll see it before it's too late, not into the deck core.

    I can't see Adwuk's purpose in drilling holes oversize. Why?

    Drill holes the size you need, and clear out core around hole c 1 - 2cm, trying to ensure as best as possible that there is a good, clear, surface on the now exposed internal faces of the two GRP layers for the epoxy to adhere to. Cover underside hole (inside boat) with tape to stop epoxy running through before its set.

    The vid below quickly shows the basics. (There is a much better one somewhere but can't find it just now. )

    Most informative bit is perhaps the brief view of his cut-away demo piece. I prefer to also give the epoxy mix, once it's in the hole/void, a poke and stir to ensure its penetrated as far as possible. Also watch out for the epoxy settling after you've first filled - may need a little top up to ensure there's enough to thoroughly reach the underside top surface.

    https://www.youtube.com/watch?v=L-Y0cIS6fSA
    Last edited by LittleSister; 17-08-19 at 00:56.

  9. #9
    Join Date
    Jun 2015
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    Tarbert
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    557

    Default Re: Adding a fitting to a cored GRP deck

    I used colloidal silica after mixing the epoxy, and thickened as far as I could but so that the mix was still pourable. Its really important if you want to avoid air pockets. The oversized hole makes it easier to remove bits of balsa core as well as ensuring that you don't get air pockets when you refill. I found that, for me, the smallest hole you can sensibly work with is about 10mm. Obviously when you refill, you will need to put some tape on the underside - ensure it doesn’t come off as it will make a hell if a mess!

  10. #10
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    Default Re: Adding a fitting to a cored GRP deck

    Very many thanks to everyone who has replied.

    The bolts are quite big so I need to be sure that the epoxy and colloidal silica doesn’t start to heat. Might be best to do two or three fills?

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