Fastening into fiberglass

[massnspace]

Over the years I have had situations where it was either necessary, or the best option, to attach something directly to a fiberglass panel (without core).

And now again I have to. This time it is a rub rail on a small trailerable sailboat. The old screw tore out and I will drill 2 new holes on each side to re-attach the rubrail. I cannot access the inside of the boat at that location to affix a nut. And I would say the glass there is about 1/8” to 1/4” thick.

Over the years I have had varying degrees of success with the following methods:

-drill hole slightly larger than screw shank diameter and screw in a coarse-thread stainless screw while pressing hard.

-drill hole slightly larger than screw shank diameter and screw in a fine-thread stainless screw while pressing hard.

-drill hole and use a coarse-thread tap to cut grooves, just like in metal, then use a machine screw to attach.

-drill hole and use a fine-thread tap to cut grooves, just like in metal, then use a fine thread machine screw to attach.

-overdrill the glass, then epoxy in a stainless nut, then use a machine screw into the nut after it is cured.

-pop rivet into glass.

The last 2 methods work the best, I think, but in my current case I have to use some type of rotating fastener directly into the glass.

So……

What is the best strategy to attach something to in-cored glass, possibly with some load on it, and have the best chance of the fastener holding over time? Any success stores, or failures, to share?

David
Seattle