recommendations- blind threaded inserts

[boatdetective]

OK- So I need to install a long skiny part on the outside of a boat- no access to the backside. The hull is fiberglass.

I'm looking for an expanding threaded insert in stainless that will allow me to bolt the rail in place without tearign the boat apart. Any thoughts?

Once again- it MUST be stainless- none of the conventional steel alternatives will do. Brass is a possibility.

[cruzziguzzi]

How much lateral force will be exerted upon it? Need it be exteranlly flanged?

Have you seen brass "Threadserts"?

A fella will want to drill the hole, fill with a resin to grab, re-drill then insert it, I've used them on fiberglass Hot Rod bodies.

Todd.

[pyoungbl]

I'd recommend opening up a hole that is larger than a standard brass insert, then bed the insert in fresh thickened epoxy.  An expanding insert will tend to fracture the fiberglass and invite water invasion into the small cracks.  That water will end up freezing and causing a greater fracture.  It won't end well. 

I had to replace most of the deck hardware on a Tartan so I don't envy your project. 

Peter Y.

[Dimples]

McMaster-Carr has many threaded inserts (search the site). Most are brass, but there are stainless inserts for plastic too.

http://www.mcmaster.com/#standard-threaded-inserts/=y18lwj

[boatdetective]

I found these threaded blind rivets- they look perfect, as they compress from the far side. The only problem is that the grip range is for thin plate

http://rivetsonline.com/rivet-nuts-and-threaded-inserts/flat-head-rivet-nuts/ribbed-l-series.html

I'll keep looking. If the hole is drilled perfectly (not too big, not too small), then a screw threaded insert could be used. It's just that biting into the 'glass is more delicate than it seems. If you are too tight, then it will cause stress risers and fatigue fracturing down the road. I'm a big believer in epoxy- but am not so sure about hardware bonding inserts in place.  Methacrylate might be better for that application.

[boatdetective]

This just might do it:

http://www.mcmaster.com/#standard-threaded-inserts/=y18qbz

[kirb]

Piaggio guzzis use 'well nuts' for a similar use on the frame. Brass is typical.
http://www.mcmaster.com/#well-nuts/=y18x71

found these:
http://www.defender.com/category.jsp?path=-1%7C10918%7C2303303&id=2303320

I do like Peter's idea of epoxy setting of a threaded insert. Should be the strongest option if done correctly.

[tris]

Back in the day when I worked for a company that built fibreglass mine hunters the standard practise was to bond in tapping plates.
Typically stainless or tuffnol depending on the load
Might be a bit of a clutz in your application but it sure as hell wont come out without half the hull coming with it 

[boatdetective]

Back in the day when I worked for a company that built fibreglass mine hunters the standard practise was to bond in tapping plates.
Typically stainless or tuffnol depending on the load
Might be a bit of a clutz in your application but it sure as hell wont come out without half the hull coming with it 

This is a repair. The builder originally screwed te rails on from the inside, then covered everything up with the FG cockpit liner. Stoopid.  I'm tring to replace the rail without tearing the liner out.  I agree, threaded plates are a good way to go....if it's original construction

[rodekyll]

I had a similar problem on my C-dory's bow rail -- rustable through-hull screws later covered by cabin paneling.  I ended up drilling through the screw holes from the outside, enlarging them on the inside, and installing stainless t-sert-type molly insert from the inside, bedded in 5200.  I covered the interior panel holes with LED cabin lights and plastic plugs.  These are removable so's I can inspect the 5200 for leaks.