Looks like Marty's question got pretty well handled here but I just replied to Marty's PM.
As I said to Marty, the worst feature of the pretty molded-fiberglass headliner is the mystery beyond it. How much gap is there can, as was said above, vary from anything to nothing. The most important thing to remember (as was said above) is that it offers next to nothing-- okay, really just
nothing-- in the way of structural support to anything. So drilling mounting holes through from topside through the headliner gets you essentially nothing more than a mess. And yet there is really no alternative for attaching anything to using proper backing blocks, which the headliner stands to inhibit you from doing.
I've contributed a few times about my bonehead/mooyock/simplest-is-smartest way of attaching backing blocks. The very
worst thing to do (and one of the most commonly-done things) is to chisel out the deck core material and to just replace it with some block of about the same thickness and area (worst, as I said to Marty, would be metal. Just:
no). The system I recommend has about three benefits over anything like that, and it's easier and cheaper.
- 1. Locate the hardware, above and below the deck. You can use one tiny (3/32"?) pilot hole through the whole system to see where it lands.
- 2. Lay out the access hole (doesn't have to be immediately below the hardware; you only have to be able to reach the locknuts through it). I suggest those plastic deck plates; I've also made a few for Diana about of varnished lauan plywood (my removable-panel material of choice). Starboard is not out of its element here.
- 3. Fabricate the backing block. My material of choice is epoxy-saturated plywood. Hardware in tensile needs wide-area, not so thick (1/2" or 3/8"). Hardware in shear needs thickness (3/4"). Attach this to the underside with a dam of 5200 round the perimeter and one long-enough sheetrock screw (yes). Drive that sucker straight up through the block, the core and the deck itself - bust it right out the other side (a tiny pilot hole helps). The hardware goes on the other side so you won't see the hole. If it breaks out a little gelcoat and laminate, that roughed-up surface is actually excellent for holding extra 5200 when you bed down the hardware.
- 4. When the 5200 is set up, back out the screw, fill its hole at the bottom with Marine-Tex (or just cover with duct tape like I do) and drill mounting holes for the hardware through the deck, through the core and about halfway into the block. Make these oversize (3/8" drill for 1/4-20 screws). Fill from the top with epoxy. This epoxy will go into the edge of the core and spread through the structure. If you have voids it may run pretty far. Sound the deck first (hammer taps) to see how far it might go. If you're worried, thicken it a little. Pump it in with a syringe. The epoxy will go into the core, will flood the gaps between the block and the underside of the deck till the dam of 5200, and fill the holes you just drilled.
- 5. When the epoxy sets up, drill the proper-sized holes through the epoxy cores and bed down the hardware. When you're done with the locknuts, fit the cover plate on the other side.
The benefits are: easy access; strength and stiffness of integral backing block; allowing the epoxy to stiffen the deck structure; elimination of potential core damage through leaks; simplicity in doing it; and a certain elegance in having it exactly like you'd like to have it.
Do this with shear loads: halyard stoppers, cheek blocks, winches (do
not bed with 5200 though), mooring cleats & bitts, cockpit-seat hinges. Do this with tensile loads: mast-base halyard blocks, travelers, padeyes (like for the vang), anchor-roller (aft ends try to pop up, not tear out). With the addition of a proper compression post, this is how you strengthen the deck for the compression load of the mast step as well.
I am still in open-mouthed shock
that Dalliance's traveler was fastened down with sheet-metal screws or lag screws and not machine screws with locknuts. No
way that was a factory job (not for that vintage anyway). I don't remember any but the 27 leaving the factory with cabintop travelers in the '70s; and the 27 had two blocks to the ends and an 'A-frame' sheeting arrangement. Most boats were designed with bridge-deck travelers, as the only proper place for a traveler is directly below the end of the boom. The H25's cockpit was even retooled to accommodate that ('78 or '79-on). But, as I always say, in most cases every PO of your boat was an idiot
so who knows whatever happened before any one of us got hold of his current boat?