Threaded insert in GRP?

[Spuddy]

I've used assorted string and shackles to cobble together a tie in place for te turning blocks on vane steering gear. I'd like something more permanent which doesn't stretch though. A friend has some nutserts but I wondered if they might crush the grp as well as grip. A trial in unobtrusive place showed they did.
The position is on top of cockpit coaming with no possibility at all of access from underneath. I'm after a pad eye bolted down to take each block. Is there a cunning device which can allow pad eye to be bolted in place?
Google found nowt suitable.
Thanks

 

[howardclark]

I use threaded inserts on (non-boaty) jigs and think if they are to bear any significant load they might be indeed unsuitable for GRP. If you do decide to try them and find rust resistant ones please let us know- I could put them to good use on wood fittings in the boat

 

[Yngmar]

Can you make access? I have some U-bolts on deck for jacklines and to get the backing washers and nuts on them, someone simply cut holes the size of a socket wrench into the inner deck layer:

 

[lw395]

Rawlnuts?
They are a rubber bung with a threaded insert bonded in.
USed a lot on GRP motorbike fairings.
Trouble is, the brass threaded insert eventually un-bonds from the rubber.

I once used some sort of rawlplug intended for plasterboard, and self tappers, it worked, but not easy to seal.

 

[Spuddy]

Fyes there are SS nutserts. I used the alu ones that came with the kit but even they crunched the gel coat.
Good idea about the cavity wall type fixing and Rawlnuts well worth looking into.
Ta

 

[Poignard]

I would use BigHeads; laminated in place with epoxy and several layers of grp cloth on top. This can all be done from the top.

http://www.bighead.co.uk/the-original-bighead/

 

[seaangler23]

There was an article in pbo not so long where someone had used these for a rubbing strip. Just drill a hole and screw it in, I'd use a bit of thickened epoxy to hold it tight. Shame they don't do any blind versions just open ended so you need to make sure you don't get epoxy on the threads

http://www.theinsertcompany.com/brass_hex_drive_insert_for_wood_headed.php

 

[PetiteFleur]

You can get stainless steel inserts with an external metric thread, similar to the ones mentioned from 'theinsertcompany' Can't remember the make - from memory they had an M6 internal thread with an M10 outside thread, other sizes may be available. Assuming a reasonable thickness of grp, tap the holes M10 and fix with a Loctite or as suggested epoxy(I would prefer Loctite personally) From experience, tapped holes in grp with stainless bolts are ok - Last year I noticed the M10 screws holding my rear boarding ladder on board were not long enough to get a nut on so I decided to remove them and replace with longer screws, penny washers and nylock nuts. I only managed to remove ONE screw, it was so difficult that I replaced it, again with difficulty and left them, deciding that they were PLENTY strong enough without nuts.
I've used these stainless inserts for threaded holes in my mast with no bad results.
OR even Helicoil inserts in stainless steel - you'll need the special taps and insertion tool so may be easier to get a firm who has the equipment to do it.

 

[anoccasionalyachtsman]

These chaps have been very helpful with a project that I'm working on. https://www.tappex.co.uk/tappex-products

And I do like the BigHead stuff in Parsifal's link. Might try them too.

 

[coopec]

A possibility?
https://www.google.com.au/search?q=...plug+inserts+brick+bolt&imgrc=1VlJsLwiMuwTJM:

Clive

 

[Plum]

I've used assorted string and shackles to cobble together a tie in place for te turning blocks on vane steering gear. I'd like something more permanent which doesn't stretch though. A friend has some nutserts but I wondered if they might crush the grp as well as grip. A trial in unobtrusive place showed they did.
The position is on top of cockpit coaming with no possibility at all of access from underneath. I'm after a pad eye bolted down to take each block. Is there a cunning device which can allow pad eye to be bolted in place?
Google found nowt suitable.
Thanks

If there is no way of getting to the back and the grp is at least 6mm thick when just tapping a thread straight into the grp will work.

Www.solocoastalsailing.co.uk

 

[ex-Gladys]

Can you make access? I have some U-bolts on deck for jacklines and to get the backing washers and nuts on them, someone simply cut holes the size of a socket wrench into the inner deck layer:

Oh God, that's a bodge that has removed most of the strength from the area... Just like the boat builder who fitted out Gladys when new... The real solution should have been to fill the void with thickened epoxy, then drill the bolt hole through that and bolt through...

 

[lw395]

If there is no way of getting to the back and the grp is at least 6mm thick when just tapping a thread straight into the grp will work.

Www.solocoastalsailing.co.uk

That's very true.
Self tappers would probably be fine, it's a matter of getting the hole exactly the right size to get a strong grip with minimum damage to the GRP.
It's a question of understanding what strength is required.
And whether that load can go into the grp at one point, or does it need spreading out?
My rawlplug bodge was when repeated use of self tappers had worn a big hole in the GRP, also IIRc the screws had rusted, which also damaged the GRP. It was a log time ago, I was about 17, fixing the toe straps back on my minisail......
But it did work, it was strong and didn't leak!

 

[fisherman]

How about: make a rectangular backing pad to suit the load, GRP/ply/S/S. Cut a smaller rectangular hole in the GRP, longest side 3mm longer than pad short side, just big enough to insert the pad and pull it against the inside. It can be fitted with a bighead nut/captive bolt/eyebolt/ringbolt/ whatever. Sikaflex to stick it in place. Refit the cut out as a filler, Sikaflex again, then cover with a S/S plate over the bolt which will hold all together, and can also be screwed through into the backing pad if necessary.

 

[Spuddy]

Thanks all! I'd been dubious about holding of tapped holes in grp but if ok for boarding ladder....hmm. thing is that layup thickness is such a var7able on old boats.
Time for another trial in less obtrusive spot with this sequence: first a rubbery rawlbolt then heave on it. Same hole might then work for threaded insert. Heave. If suspect then fushermans surgery.
Thanks again

 

[Gordonmc]

I use Rivnuts on the car with some success. Its a fiberglass bodied motor and the Rivnuts have replaced most of the blind nuts where needed.
I use aluminium Rivnuts but they are available in stainless. They go up to at least M12 in size.

 

[DinghyMan]

There was an article in pbo not so long where someone had used these for a rubbing strip. Just drill a hole and screw it in, I'd use a bit of thickened epoxy to hold it tight. Shame they don't do any blind versions just open ended so you need to make sure you don't get epoxy on the threads

http://www.theinsertcompany.com/brass_hex_drive_insert_for_wood_headed.php

I've just been testing a few different types of their inserts for use in acetal & delrin; screw in ones seem best but the push in ones that then expand when you screw into them are way easier to use. I made an installation tool for the screw in ones which kept them straight.

 

[PaulRainbow]

If it's solid GRP i can't understand how you are crushing it with an insert

 

[Daydream believer]

The turning blocks on my Aeries are mounted on adjustable lines fitted to the gunwhale such that the blocks sit just inside the cockpit.. I have an aluminium toe rail but if you have a wooden rubbing strip you could think laterally & fix to that instread. Although on lines which are 9 inches long they do not move from side to side much & i can adjust the line tension on the steering lines very easily by adjusting the turning block lines. You may just need to screw an eye to the timber
Perhaps that may provide an alternative solution

 

[Kelpie]

The turning blocks for my Navik were simply cheek blocks mounted on top of the coaming with a couple of self tappers. As the load was in shear there was no tendency to pull the screws out and it worked perfectly for several years until I sold the boat (and put thr Navik in the shed... really must get around to fitting it to the new boat!)