That structure could be a deck, coach roof, bulkhead, whatever.
There is in this forum a coach roof built with ply-foam-ply, way to go too, insulation and light weight high up in the boat.
So you forgot to sandwich a block in the structure huh.....
or want to add something later as the $$$ comes home.
Drill, drill bit, 1/4" (6mm) alan key. (ok, Allen) and a large syringe - from a vet is always good. Elephant size.
First draw an outline (foot print) of the item on the panel. Drill the fixing holes ONLY through the laminate into the foam the item is to be fixed too. DONOT at this stage drill right through (if you are to bolt through the deck, coach roof etc) no problem if you are only screwing to this laminate (be it ply, fibreglass etc)
Then in the center of this marked out area (to be finally covered by your item) drill a 3/8" (10mm) hole - again only through the laminate as explained above ok.
Grab the Allen key, put the long end in the drill chuck, the short end push into that 3/8 (10mm) hole and let ér rip!
Got it? Vac out the foam. If the short end of the Allen key isn't cutting it then stage 2 is to either make up one with a short length of Kiwi number 8 wire (pm me for kiwi 3" of #8 wire $248.98 each
- gladly email you one
) that has a longer short end.....enough to flog out the foam past the item's fixing holes. To what ever size you want. No rules here.
Just move the drill up and down to mush up that foam to aid vac'ing it out the 3/8 hole, bigger cavities need more room to put the longer short ended Allen key in, so, careful starting the drill.
Vac out the rubbish, helps if you don't cover the fixing holes with the vac pipe, the holes aid in letting air rush through helping rubbish to vacate. Step up the length of the short ended Allen key for a larger cavity in stages and vac as you do.
Now mix up some epoxy resin with talc or hard filler - runny brew ok (for screws to get a good bite on & through bolts wont compress your lovely finished laminate.
Grab the syringe, fill it up with your epoxy mix, squirt it into the 3/8" hole slowly.
- Tip - I use a firm rubber (skool type) & drill a hole through the center, a little smaller than the elephant syringe tip, to poke the syringe nozzle into, then hold firmly over the 3/8 hole squirting epoxy slowly until it is seen coming out the fixing hole you drilled way back when (before you fell asleep reading this - see males don't do instructions very well aye)
There's something I forgot here....... oh yea, masking tape, all over the surrounding area as that poxy stuff (like sillycone!) goes every where! Chit I hate that stuff.
You could, on larger item foot prints, drill several 3/8 holes, but I woodn't go bigger on that hole the Allen key is spinning in, the hole is keeping the Allen key from going ballistic ok. Also it's easier to cover up the hole after the poxy has been squirted in. A 3/8 bolt with masking tape rapt around 4 or 5 rotations and pressed into that hole will stop poxy exiting without permission.
To stop the poxy stuff emptying out of your wonderful job, poke screws or a helpers fingers, in the fixing holes after poxy has started exiting - one at a time if that's how it works out ok, especially on a vertical or sloping laminate - bulkhead etc. Masking tape wont cut it, first it'll stick, for about 1 minute, then like your helper being bored poking fingers in those holes, it will slope off and your wonderful job will vacate it's epoxy.
On another note....
Probably not a good idea. Huh?
Heard you thinking see, don't put the item and it's fasteners in the epoxy before it has set.....
I know it's a good idea, not!
Well, the plurry thing won't come off for real, never!
And it's in the wrong place anyway aye lol..... see, I've done it lol.
Anyway the fasteners do break and then what? Or the seal goes pear shaped and leaks, etc.
It's too permanent.
Feed back welcome!