Attaching A Dodger Frame

[Dallasron]

So I have my frame ready to attach however on close inspection, Where the main bow will attach to the coachtop, It is only fiberglass without a core. So I need something like a stainless molly bolt that will spread on the back,

Has anybody source something like this?

Thanks in advance

[psk125]

You will want to install it with regular bolts with washers and big backing plates in order to spread the load. Mollybolts were developed to use in drywall, and work by expanding the casing against the sides of the hole. Because of this, a mollybolt would end up cracking the solid fiberglass surface it was in if it was tightened enough to have it hold. You may mean toggle bolts, but these would require bigger holes in the coach top to install them- which means leaks. The toggles might cause point loading that would lead to cracks too. Regular bolts with washers and backing plates are the way to go. People are going to be almost doing chin-ups on this thing. It needs to be solidly secured.

[Dallasron]

Agreed. My problem is that I can’t access the underside

[siamese]

My first inclination would be to use the largest/appropriate stainless steel screws of the appropriate length. And, to use care to select the right size drill bit to get a good bite without putting too much stress on the glass and causing a crack in the gelcoat.

Seal/adhere it with 3M 4200 or equivalent. The good news is, if a little moisture should get through sometime in the future, there's no core there. Great.

I'm thinking of the forces exerted on a dodger frame with the dodger attached. Seems like most of the forces would be from the side or downward. In either case, the fasteners would be acting more as pins than screws.

note: I'm pretty sure the previous owner of my boat would have just used nails.

[Dsanduril]

Depending on the exact situation you might be able to use a RivNut:
https://www.mcmaster.com/rivnuts/

Depends on the thickness of the FG. And it won't really distribute the load. Essentially it creates a threaded hole in the FG. There are some made with a seal under the head, but otherwise install with sealant and then install foot and bolt of structure with more sealant.

[Dallasron]

so at least I am planning on 6 pts of anchor, 2 front and center set in epoxy, the 2 on the sides with the angled foot, and 2 more struts to anchor the back. Will have handholds on the sides for even more rigidity...I am thinking maybe drill an oversized hole and shove a drink umbrella in, open it, fill with epoxy. then screw to epoxy.

[JPA Cate]

Actually, you could cut access doors in the overhead, use a little teak trim to pretty them up... The nuts, bolts, and backing plates is a very much better idea than screws, which, ultimately will come out by themselves.

Ann

[RaymondR]

Or glass some pads to the fibreglass that you can screw into.

[AKA-None]

Originally Posted by JPA Cate

Actually, you could cut access doors in the overhead, use a little teak trim to pretty them up... The nuts, bolts, and backing plates is a very much better idea than screws, which, ultimately will come out by themselves.

Ann

This what I did
Well not exactly as I haven’t made the pretty it up parts yet

[flightlead404]

Originally Posted by Dsanduril

Depending on the exact situation you might be able to use a RivNut:
https://www.mcmaster.com/rivnuts/

Depends on the thickness of the FG. And it won't really distribute the load. Essentially it creates a threaded hole in the FG. There are some made with a seal under the head, but otherwise install with sealant and then install foot and bolt of structure with more sealant.

These things are awful, but sometimes the only solution. Get a good built for purpose puller. But you will inevitably end up with a "spinner" which is a giant PITA to deal with.

[Jack C]

Here is a different approach that I used when installing a windvane. It may be an overkill.
Drill a large as possible hole under where the bimini fitting will sit. Prepare a backing plate having a width less than the hole diameter. The backing plate has tapped holes spaced exactly the same distance apart as the screw holes of the fitting. The threads must match the machine screws (flat head ) that you will be using. Use the fitting to mark for the screw holes on the deck and drill holes for the screws. Countersink slightly. Then attach a thin string to the center of the backing plate, drop the plate through the big hole and use the string to hold it to the underside of the deck. Then get screws through the deck into the threaded holes of the backing plate using the string to hold the plate up against the underside of the deck. Fill the big hole around the string with thickened epoxy. Seals the hole and holds the string. When dry cut the string. Remove the screws. Put butyl under the fitting (the countersinking will create a great o ring type seal) and underneath the heads of the screws. Then screw through the fitting into the backing plate.

[mitiempo]

Originally Posted by JPA Cate

Actually, you could cut access doors in the overhead, use a little teak trim to pretty them up... The nuts, bolts, and backing plates is a very much better idea than screws, which, ultimately will come out by themselves.

Ann

Ann has the best solution.

There is nothing un-seamanlike about access panels in the overhead covering washers, nuts, and backing plates.

[TrentePieds]

Ann and mitempo are absolutely right. Don't mickey-mouse it when a little thought and an extra hour or two of labour (your own, and presumably costless) will give you a professional (looking) job.

A pic of a common kind of access cover is attached. To install it in the liner is a piecacake.

To fabricate a backing plate for the attachment hardware for the dodger bow is also a piecacake which you can do with a common hacksaw, a file and a drill motor with the appropriate bit. A scrap of, say, 1/8" SS plate will do nicely, but remember to go slow with the tools. Low tool speed and lotsa pressure is needed. Lubricate as you go. WD40 in a spray can will do the job.

I would use the biggest size machine screw you can accommodate in the holes in the attachment hardware. I would drill the backer with the bit appropriate for the tap matching the thread of the bolts, then tap the holes in the backer. That way you avoid fiddling with easy-to-lose little lock washers and nuts while working in what is bound to be an awkward position.

Let's know how you eventually get the job done, plz :-).

TrentePieds

[RaymondR]

There's nothing wrong with curring a hole or better a slot through which a rectangular plate can be installed and fixed in place with a couple of screws and the drilling and tapping through the outer hull to fix the base of the bows to the deck without cutting holes in the inner liner. I've done it fairly often over the years where I could not get access to the back side. I usually use a slot rather than a round hole and use alloy flat bar. I tend to use dental floss to pull the plate into place as it's very strong and slips out easy and even allows screws into the tapped holes without it's removal.

[flit]

My understanding is that you can not reach the underside for a nut, washer, or backing plate?
If that is the case, I do not recommend cutting access holes and covering with Pie Plates. Every pie plate we have used (Beckman, Todd, and Bomar) has leaked when off shore. Use them only in protected locations. They also compromise deck strength to some extent and trimaran decks are often engineered for strength and weight is kept low. There is risk depending on location.
Anyways... A far far better solution is to carefully take an area down to exposed glass laminate. Then epoxy bond a good thickness G-10 glass plate at the mounting foots location then drill and tap that plate. If you want to be ultra secure. Take a 1" hole saw and drill a hole, remove the core in a widening wedge shape down to the inner skin. Then refill with broken DB600 fibers or mashed up matt very densely packed and mixed with epoxy built up in layers to avoid overheating (chopped fibers if over 12mm are also your friend here) Cover last layer with a hot epoxy bonded G-10 plate as above. Then drill and tap the whole thing. Alternately you could embed a stainless nut/washer in this mix, leave machine screw attached in the buildup with mold release wax on the threads and have an embedded fastener nut to sink into.
As a side note... We have an Iverson's dodger and a cedar cored deck on our Farrier F36. Iverson's only used 15mm and 20mm long wood screws to attach most everything into our core..;. they seem to be getting away with this approach without any reproach that I notice on the Forums. Our Bimini forward brace pulled out of the deck, so this is NOT a viable attachment method and you should do better.