attaching wood gunnels to foam sides

Discussion in 'Fiberglass and Composite Boat Building' started by Tungsten, Feb 27, 2014.

  1. Tungsten
    Joined: Nov 2011
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    Tungsten Senior Member

    Thinking ahead and before I glass up my sides I was wondering what may be the best approach to attach inner and outer gunnels to foam?They'll be 1 1/4" wide and 5/8 thick.I was going to drill out some of the foam every 6-10" or so and add a hard filler then glass both sides.Do I just pre drill through these epoxy filled spots after cure or is there a better way?

    Thanks,
     
  2. groper
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    groper Senior Member

    why not glue the wood to the foam using a moisture cure polyurethane adhesive, then glass over the whole lot permanent. Getting rid of fasteners is a good idea unless you have to have them removeable for some other reason?
     
  3. alan white
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    alan white Senior Member

    Why not fill the top 5/8" of the hull with solid wood? Leave a little (1/16") above the wood filler strip to fill with epoxy. Wrap with glass and then add the gunwales.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Yes, you have the right idea, drill an over size hole on 6" centers, unless the hull hasn't much curvature, then redrill for the rub rail and inwale through bolts. You really don't want to glue the rub rail on, as it's a sacrificial piece and it'll need to come off every so often, so it's bedded in polyurethane or polysulfide.
     
  5. Petros
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    Petros Senior Member

    I would not predrill the holes, you will be tying to match drill them blind. very bad idea.

    I suggest boring out an area much larger than the hole for the fastenr, as much as an inch larger, fill the hole completely with epoxy and filler mix, sand flush with the surface, and than glass over the last coat. carefully mark the top edge in someway so when you have the gunwale and inwale clamped in place that you can match drill all the way through you can see where to drill by the mark on the top edge.

    this way you will have perfectly placed holes in all three pieces. And the hard filler/epoxy mix will prevent you from trapping moisture in the layup and prevent it from being compressed and damage the layup.
     
  6. alan white
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    alan white Senior Member

    By the size of the gunwales indicated, the boat is not very big. It would almost certainly be dry-sailed. There would be a difference between this boat's construction and a heavier cruiser. Maybe it would be a lot of extra work to plug the screw holes afterwards. The thickness is only 5/8" so the screws would have to be set to allow for bungs and countersinking. Maybe 3/8" of wood the screw is passing through.
    Therefore, it makes more sense to eliminate bungs altogether and allow the fasteners to show. The screw ends could be ground off on the inside with whatever desired outside. Varnish or paint should seal the screws well enough, though a swab with epoxy would be a good idea. I mentioned the idea of a solid wood core the thickness of the foam. The gunwales get clamped on and drilled, the holes coated with epoxy by means of swabs, cure, apply 3m 4200 if desired, and send the screws through. Sand and the three pieces of wood will appear to almost be a single piece. This has to be a nicer look than glass over foam. Of course the screw holes through the foam could be epoxy-jacketed. but again, it's probably a dry-sailed boat. And it may be it's going to be painted, so the hull top edge will just look like the gunwales.
    Avoid epoxying it together too permanantly by removing the gunwales prior to swabbing epoxy into the holes. Elsewhere there's a forum thread about coating limber holes with epoxy. I am saying if there's merit in coating limber holes that way, surely applying that method to gunwales makes as much sense (you don't have to deal with constant sloshing water that doesn't drip or dry easly either).
    You're not protecting wood, but foam insofar as the hull material is concerned. This is at least less of a concern than a solid wood hull would require.
     
  7. Tungsten
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    Tungsten Senior Member

    Thanks,yes the boat will be about 19' LOA.Gunnels attached permanently with epoxy.

    I'll no doubt try to steam the wood prior so the bending force won't be too much.

    My concern is the bigger holes filled with thickened epoxy will be right at the edge with 600gsm cloth on each side will this be enough since it will take some force to bend the wood in?

    I was going to attach the in-whale first with short screws to hold in place till epoxy cures,then remove and attach the outer with a longer screw from the outside into the same hole.countersunk and bunged.Maybe easier said then done lining up into the same hole.Inwhale screws could left in place and just offset outer screws I suppose.Just need a few more epoxy inserts I guess.
     
  8. alan white
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    alan white Senior Member

    If you are epoxying the gunwales on, you do not need any fasteners.
    You need a lot of clamps. Spring clamps are best because they don't squeeze too hard and starve epoxy joints. You also might benefit from a slow epoxy hardener if time isn't an issue.
    You're right about doing one side at a time. Use masking tape liberally. I am guessing the boat is a dory based on the gunwales dimension of 1 1/2" high, which lie naturally along the sheer without much if any up-bending at the ends.
    You won't need any fasteners to attach the inwale. You might mix up a small batch of epoxy with some sand in it and roll a thin coat over the gluing face of the inwales and outwales the first day. The effect will be the gunwales will not slide when the clamps are applied and also a slightly greater glue gap will be created.
     
  9. Fanie
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    Fanie Fanie

    WHAT :eek: You're going to leave screws in :eek:

    Oh boy, just wait till Par gets here...
     
  10. Tungsten
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    Tungsten Senior Member

    LOL!!

    Great tip with the sand,however there will be some curve to the sheer so something has to hold them while you try to bend them in.Nothing worse then getting to the end to only realize the other end has slid up a bit.

    similar lines to this.

    [​IMG]
     
  11. Fanie
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    Fanie Fanie

    I see, it's an ancient Egyptian bath tub, you want to put foam in so it would become an ancient Egypt sofa. Bloody kinky bath for three, what's the hole in the center for... sorry no I shouldn't have asked :D

    On second thoughts, I can see the drum beater with the whip sits at the bow chair, the slave sit at the oars and the aft seater does the rudder. Even has a book shelf when the other two starts something they can't finish at least you can read...

    Never saw the likes, all I can make out are the two rod holders port and star, nothing else -

    I give up, what is it ? !
     
  12. SukiSolo
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    SukiSolo Senior Member

    One way I have used for clamping gunwhale strips is to use F clamps in a slightly different way. If you have horizontal surfaces ie deck and packing to the hull you can tighten the clamp and use the actual bar itself to push the gunwhale strip against the side. You need a bit of pressure to do this so pads may be needed. Imagine the clamp vertical so the 'flat' bar of the clamp becomes the part forcing the wood towards the hull.

    An alternative is to leave it at a distance out and drive in a wedge, however with stock of 10mm (3/8") I have bent even solid Sapele directly with the clamps.

    Of course it depends how the deck/hull/gunwhale is configured.
     
  13. alan white
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    alan white Senior Member

    Better if you hadn't parked that dory between two tankers. But seriously, that doesn't look like an easy bending job. I'd almost try doing it in four pieces...
    Well, what is it?
     
  14. groper
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    groper Senior Member

    Your mad... id make the whole lot from foam... bending clamping and glueing is a snap, then glass over the whole lot, no screws, no issues with wood and water ingress...
     

  15. alan white
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    alan white Senior Member

    You may be in for a nightmare unless you divide those gunwales into 5/8" x 5/8" pieces. Then you won't need to worry about the clamping part. You'll be able to bend those pieces around that sheer without screws or special clamping tricks. Minor steaming will be a snap. Do the top pieces first and wipe excess away where the bottom piece is to go. The seam should be invisible after sanding and finishing.
    Just looking at that crazy sheer and I can see what could turn out to be quite an undertaking.
     
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