pop rivets & fibreglass

[decdeb]

Being new to working with fibreglass, there is still a lot I need to find out. I am aware that self-tapping screws into fibreglass is not a good long-term solution and that bolting through if possible is best. However, I was wondering has anybody tried to use pop-rivets and if so what was the result?
Thanks,
Declan.

 

[boatbuilder]

Re: pop rivets & fibreglass

a leak /forums/images/graemlins/smile.gif

 

[ShipsWoofy]

Plenty of small tenders have pop rivets holding the deck molding to the hull. Light weight work really.

For heavy mounting I always use nuts and bolts, understandably there are going to areas where access to the rear is not available. This will mean blind mounting or re-location to somewhere with access.

What I do not understand is why you would substitute a self tapping screw for a pop rivet, IMO the screw is the better solution, mainly as it is removable, stronger in most cases, does not leave a hole down the centre.

I have many items on board which use screws for fitting, some as long as the age of the boat, 29 years now eek, not a long term solution, how long do you want?

I have no pop rivets anywhere but the mast and boom, oh and my tender some of which desperately need replacement, the heads do 'rub' off with wear.

I will continue to use screws where appropriate.

 

[Sixpence]

Poop , I hadn't even thought about the hole , so are we saying nut and bolt whenever we can , and if so , 316 ? , or will something else do the job ?

 

[ShipsWoofy]

I have a mixture of A2 and A4 fixings. I will as much as possible use A4 (316) outside. Though I have a few A2 fixings on the deck which, being polished have not formed surface rust yet.

Though, I have a couple of bolts on my rudders which although show no signs of corrosion are leaving a rust stain where the water runs down. I will change them, but as these are 2 dozen large bolts I would rather spend my cash elsewhere at the moment. I have a piece of A2 stud in my mast base which is clean as a whistle... so application dictates.

Screws in wood fascia I try to use brass, it looks far nicer.

When I took the boat over there were a fair few mild steel screws used inside. I have replaced most of them, 70% were actually in good clean condition. Hence, I think A4 all round is a bit of overkill, A2 screws are much cheaper if buying in bulk from the jumbles (A2A4) or screwfix.

I am not a metallurgist so can not comment on strength of metal for applications, if indeed it makes any difference for small fixings.

I would have thought for you with a classic wooden boat you would be buying brass, copper and bronze by the sackful though??

 

[cliff]

I do not use pop rivets into fibreglass without a load spreading washer on the "blind" side to spread the load imposed when breaking the rivet shank. Even at that I have found pop rivets are a poor substitute for self tappers. When using self tappers take care to drill the pilot hole to the correct size - too large a ø and the screw will not bite too well, too small a ø and you run the risk of cracking the fibreglass. Also, use a reamer or countersink if you have one to chamfer the outside of the hole slightly to avoid gel coat damage.
--------------------

"Artificial intelligence is no match for natural stupidity"

 

[Sixpence]

Lost the big one I'm sorry to say , had me tearing my hair out at the time , lots of blood and tears , and probably upset some on the forum too .
Back to the 25 ft Birchy now , intended replacing the mild steel window bolts with rivets , but there isn't a lot of GRP for bolts to hold on .
Quandary time , what the hell do I use? , this is getting very deep for the time of night

 

[William_H]

If it is a blind hole attaching something I feel that self tapper screws would tend to crack split crush fibreglass. I think using a thread tap and cutting a thread then using correct size SS screws would be better bet. Pop rivets would not hold very well without a washer behind the f/g and if you can do that better to use screw washer and nut. olewill
PS I use the thread tap a lot as it provides a better seal against water (seal it anyway) and it will hold a screw tight while you fit a nut and washer on the inside. Saves needing 2 people.

 

[marcusgillies]

Fairline tended to use loads of pop rivets in the 70's and 80's alot of which are still ore ok today however unanodised aluminium and salt water arnt really a good combination and some do tend to fail.
In the case of self tapping screws into fibre glass the trick is to use a counter sink bit and take some of the gel away from the hole to stop it splitting and also using the correct size of pilot hole, the last trick in not to overtighten the screw til it looses hold but stop when the fitting becomes tight. obviously seal!

 

[fdmarsden]

If you can get top the back of the moulding, the nylon wing nuts sold by Holt-Allen are very good, the shape of the item spreads the load; the nylon works like a lock nut. Use a self tapper in them

I have used them a lot, never had one fail, even in quite high load conditions, e.g. dinghy toestraps

 

[oldharry]

[ QUOTE ]
I am aware that self-tapping screws into fibreglass is not a good long-term solution

[/ QUOTE ]
Why ever not? Any lightly loaded fitting or fastening can be screwed in using self tappers. Through bolting is only needed for heavily loaded fittings such as cleats. Pop rivetting is used sometimes in building to join two mouldings for example, but not for fastening small fittngs.

Rule of thumb is that if would be safe to use wood screws in wood, then you can use Self tappers in GRP. Bolting is always the strongest option of course.

The problem with rivetting is that once fixed they are very difficult to remove. Why give yourself work in the event the fitting becomes damaged or worn? You also need to be careful in the marine environment of the mix of metals. Many rivets are aluminium which itself is fine, but creates havoc in contact with other metals, especially stainless, without considerable precautions. With self tappers, it will be stainless fitting with stainless fastening.

 

[Topcat47]

Pop rivits are not a good solution for GRP. To be really effective they rely on the combination of elastic properties of the rivit and the joined materials. Marine applications should be Monel, although you will find that monel is harder than aluminium. When used to secure dingy hulls and decks it relies almost exclusively on the tensile strength of the rivit and the coefficient of friction around the joint between the mating surfaces. Never put a pop rivit into a blind hole in GRP.

This is by way of a "starter for 10". I've seen polyprop dinghy's fastened by pop rivits too. I haven't bought one.

 

[snowleopard]

Re: pop rivets & fibreglass

I use loads of self-tappers in GRP and have done for years. I even secure all my grab-rails with them! My boat is built of foam sandwich and it is often easiest to screw into one skin rather than drill oversize, solid-fill the core and re-drill to put a bolt through. It also has the benefit of preventing leaks!

The key is to drill the right size hole. I stick almost exclusively to No 8 screws for which the correct drill size is 3.5mm.