Seat mounting foam core deck

Discussion in 'Materials' started by gtflash, Nov 6, 2016.

  1. gtflash
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    gtflash Senior Member

    About to mount some offshore style bucket seats to the boat. Originally the bases were mounted using multiple self tappers. My initial thought was to drill a hole, remove foam core and fill with thickened epoxy, then tap and use a machine screw.

    On another forum this idea doesn't seem popular and the trend is to fit large blind stainless thread inserts. These have a thread on outside and inside. I'm a little confused now

    It's an offshore fast boat, with no rear access to underside of deck
     
  2. gtflash
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    gtflash Senior Member

    Suggestions include using veck ra300 and sp spa bond 345 to "glue" mechanical threads into deck. I have never used these products
     

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  3. waikikin
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    waikikin Senior Member

    Maybe you can install some access to the underside so backing plate/s or large washers can be fitted, and also decore and form an annulus with higher density filler material. With composite the more fiber you can share the load to the better, busting a seat off especially a pedestal style one could led to injury, sounds like they were in failure mode last time..

    Jeff.
     
  4. jorgepease
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    jorgepease Senior Member

  5. gtflash
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    gtflash Senior Member

    I think I am going to drill deck, remove foam and epoxy in between the sandwich. Considering setting a thread in to epoxy
     
  6. jorgepease
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    jorgepease Senior Member

    I had the same concern, I did the same research and found that tapping thickened epoxy was a short lived solution. Better would be to do the same but embed threaded inserts. I did this on one project and it's still holding. I bought them a McMaster Carr I believe, On the toggles, it requires drilling a big hole but once inserted you can fill with thickened epoxy and you get a nice solid anchor that is permanent. This is what I have on one boat now and it's solid!
     
  7. JSL
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    JSL Senior Member

    Tapping epoxy not good. Through bolt with compression sleeves and backing plate. Make sure seat has a good mounting face as well.
     
  8. missinginaction
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    missinginaction Senior Member

    A few years ago I needed to mount a couple of helm seats on my flybridge. I didn't want to drill through the cabin top because I didn't want the fasteners to show inside the boat and holes invite water leaks evenually, even with the best sealing.

    I ended up making two plates out of mahogany, about 12" X 12" or 30cm X 30cm and about 15mm thick. Pretty easy to make with a table saw, jig saw and a router. I then used stainless steel "T-Nuts" to secure the seats to the plates.

    The pedestals are 23cm in diameter. Locate the pedestals on the plates, locate the holes for the fastening bolts and mark the plates with large cross hairs. Then over drill the holes and fill the over drilled holes with epoxy ( I use packing tape to keep the resin in the hole until it cures).

    Once the epoxy has cured drill a proper sized hole for your t-nuts and install the nuts from the bottom of the plate. This technique produces an "epoxy grommet", water can never get to the wooden plate. Run a machine screw or bolt from the top down through the pedestal and into the plate/t-nut and you're done. I use a little threadlocker just to insure the bolt doesn't loosen from vibration.

    You can finish the plate with three coats of resin, glue it to the deck with thickened epoxy, then fair it in, paint it to match and you're done. Put a litle packing tape over the bottom of the plate to keep epoxy out of the t-nut threads. This technique works well if your deck is curved for water drainage. You can make a pad out of thickened resin and vary the thickness of the resin base depending on the curve of the deck or roof.

    This takes a little longer than just bolting the pedestals down but when you're finished you have a permanent installation that is extremely strong and will never leak.
     
    Last edited: Nov 20, 2016
  9. gtflash
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    gtflash Senior Member

    Would large self tappers work into epoxy corks between the skin of the deck?
     
  10. Jim Caldwell
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    Jim Caldwell Senior Member

    Not for long!
     
  11. jorgepease
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    jorgepease Senior Member

    What kind of seat base is it? Does it have four legs or is it a pedestal. Obviously with four legs you have much less forces to deal with, you might get away with it on a bay boat, for a while, but for offshore I would feel more comfortable with toggles and I would still hollow out the foam around the hole and fill it with thickened epoxy, pretty easy to crush the core when you tighten the bolts.
     
  12. gtflash
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    gtflash Senior Member

    It is basically a stainless upside down u shape 8x6inchea with 6 fixings to the little angle bits. This bolts to the deck. Then two bucket seats bolt to that. Boat is reasonably fast at 65knts.

    I can't work out in my head how to epoxy a toggle bolt in place and still have access to the toggle bolt. I have found a big head, which is blind, 30mm square base, female thread. I will hollow out the deck and epoxy this stainless big head in place with just the top of the female thread part poking through deck. Epoxy thickened around the big head and wider than the hole in between the deck sandwich. Then make good the deck. Sound ok?
     
  13. jorgepease
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    jorgepease Senior Member

    Why won't those toggles I posted the link to work? They stay in place without the bolt, you put them in, slide the retainer cap down and snap off the legs. Then put your seat in place and drop your bolts in. You don't need access from under the deck.
     
  14. gtflash
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    gtflash Senior Member

    So do I put them in the core area? Or below whole sandwich? I couldn't work out how I would epoxy them in place. It seemed to make my head hurt
     

  15. JSL
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    JSL Senior Member

    Perhaps a photo of the seat, frame, etc. might help some participants get a better idea of the installation. 65 knots is fairly fast so the forces could be significant.
     
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