Surface mount grab bar in fiberglass

[jerrypeters]

Hi All. I would like to mount a stainless grab bar on the deck of an open sided sugar scoop on my catamaran. It is not possible to get to the underside of the deck in order to use thru-bolts and backing plates. So, I want to try to surface mount it.

The deck is solid fiberglass of unknown thickness. My preliminary list of options include stainless lag bolts, tap and thread the fiberglass and use machine screws, use some epoxy product like Weld Mount or JB Weld or other, combination of epoxy and screw ...

There will not be very much tensile of lateral stress on the grab bar. It is intended for use as a handhold to allow the dinghy driver to hold the dinghy tight to the sugar scoop while passengers embark/disembark.

Thanks for sharing your experience.

[bil56]

your bridge, in grp foam sandwich?

[jerrypeters]

I have two surface options. One GRP foam. The other solid glass.

[JBP]

Threading the fiberglass will probably strip easily. Lag bolts/wood screws may hold a bit in solid glass, but only if it's pretty thick, say 1/4 inch or 6mm. Foam core is best because it is thick and you can replace the foam with epoxy before screwing. I would do the undercut trick for extra strength (using a angle hook such as a hex key in a drill to remove the core without removing the outer layer.)

You could also epoxy in stainless nuts and then bolt into them or try toggle bolts.

[Rotten Ricky]

Originally Posted by jerrypeters

Hi All. I would like to mount a stainless grab bar on the deck of an open sided sugar scoop on my catamaran.

There will not be very much tensile of lateral stress on the grab bar.

Jerry,

Solid base is preferred. You could use threaded inserts installed in the base material and then use machine screws into that. Inserts are like a pop rivets, using the same kind of tool, expanding from behind the base to stay locked in place. Most are aluminum but if you use a corrosion resistant compound between stainless machine screw and the insert it should be fine for many years.

You can also buy stainless, aluminum and nylon self-opening inserts that expand behind the base that do the same thing, just as in a building. There are various qualities, but good quality nylon ones tend to use self-tapping screws and are also quite robust.

Be aware that either solution often leave the outside of the insert proud (on top of ) the base surface and that will not allow the grab rail to sit down flush on the base surface. You will need to provide a thin piece of gasket or something to allow the rail to sit down solidly on the base material. A better option is to put a slight recess in those base surface holes before installing the inserts.

Do not simply use a larger drill bit in an electric drill to do this or it could give you a poor irregular recess recess as it wanders around, or it could also grab and tear that surface badly or make the hole so big it is unusable. Use an inexpensive countersink tool/bit instead.

I prefer the better option for the recess of using a spade-type bit instead of a countersink tool BEFORE you drill the final hole, if the base material is thick enough for this to be done. This would give you a flat rather than a tapered surface for the insert to sit into.

Cheers, RR.

[tkeithlu]

Stainless steel rivet nuts are available; see below.

Note the suggestions lead you to finding a way to grip the hull rather than gluing to the surface. If you've just gotta glue it, use epoxy paste such as MarineTex, and squeeze it both into small drilled holes in the hull and the screw holes in the grab bar.

https://www.amazon.com/Stainless-Thr...a-599095114253

[thinwater]

Rivnuts. Trivial hold in fiberglass/foam.



Unless you get something behind the inner skin, you are limited to the tensile strength bond of the outer skin to the foam, which is 500 psi on the best day and probably near zero after it gets smacked a few times. I doubt these is a bonding or sealed hole trick that will reliably get you close to grab bar strength in the long term. The problem is the leverage on the grab bar and the chance of it getting kicked hard.



Is there space behind the deck? There are plenty of hollow wall grab bar mounts for showers, all stainless or non-corrosive, and rated for the load. Google and pick the one you like. Big stainless toggles are another possibility. Much depends on the design of the bar.


A cored deck is stronger than drywall, to be sure, but the top skin is just glued on.

[contrail]

I used to epoxy a fitting (don't know the name), that was a stainless tube, and threaded inside and out, maybe a half inch long or longer, into solid glass. I just drilled to fit and then screwed them in, with the outside coated in epoxy. Then it was simple to screw a machine screw into the threaded inside. These held pretty well. Didn't look anything like what thinwater is showing, but maybe he has used these, too?

[Flatswing]

No doubt the previous suggestions are strongest. However, they seem like overkill for your intended purpose. If you have a core at the site of your mounting location, drill holes at least twice the diameter of your intended fasteners and fill full depth with thickened epoxy or Thixo to seal the core. Next day drill for #10 or (even better) #12 screws so that the hole is just big enough to turn the screws in by hand. It’s a bit of a pain, but if you use power, you will crack the epoxy, diminish the holding power and worse, lose the seal to the core. Increase the drill size by 1/64” increments till you can turn them in by hand. Countersink a dimple in the epoxy to leave a seal of butyl or your favourite sealant under the fitting and around each fastener.
All my (50lb+) bulwark/transom doors & bow rails are mounted with screws. I can sit on them unlatched and they don’t budge if done correctly. I have added several grab rails to my transom where it’s impossible to through bolt. Each rail, 2x #10 screws, solid as a rock. Amazon has several very nicely made 12” 316 SS grab bars with screw mounts.

[jerrypeters]

Thanks all. Lots of good ideas.