bolting to GRP cavities

LadyStardust

LadyStardust

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14 Oct 2004
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159
Location
Chiapas, Mexico
sistermidnight.co.uk
Sorry but I couldnt think of an appropiate title.
I need to lift my stanchions and rebed as they are old and leaking. However they have 2 aditional bolts on a horizontal supporting strut that bolts to the inside face of the bulwark. If i remove these bolts the nuts behind fall of into a cavity which can only be accessed by destroying large sections of the boat interior. God knows what the builders where thinking when they glassed this section in. What I would love to discover is some kind of stainless steel cavity fixing, like the type used on Plasterboard walls which would work on fiberglass, I expect I'm not going to find a solution but thought I should ask before I get the chainsaw out
Does anyone perhaps have a machine that can shrink washers and nuts by 25% for a few minutes ;-)
 
Can't help with your main objective.

However, if you can undo the bolts does that mean you can get a spanner to hold the nut? and if so can you not fabricate something to capture it before it falls.

If not accessible then is there a chance you can undo the bolt(s) sufficiently to saw of the head of each one thus creating a stud on which you could fit a nut in substitution.

Probably no use but worth suggesting I thought
 
That's an interesting one! I wonder how well sealed the cavity is. Might it be possible to drill a small hole near each stanchion and inject plastic foam? This might hold the nuts in position well enough to be able to refix the stanchions.
 
Hi, there are fixings called 'rivnuts' which are threadded inserts which work like pop rivets. You drill an appropriate hole, insert the fixing and clinch it with a special tool which spreads the fixing behind the panel, leaving a thread to take your screw, they are available in mild and stainless steel and aluminium. Wurth UK also do 'rubnuts' which are similar, but are made of rubber with a brass threadded insert and don't need any special tools. I have used both types and they work very well where you can't get access to the rear of the fixing.
Peter
 
Is it possible to undo the bolts sufficiently so that the nuts are still attached but so that you can get to hole? If so, and the hole is large enough, perhaps you could squeeze some superglue into it onto the back of the nuts and then pull the bolts tight to glue the nuts into place. You can then take out the bolts and if all goes to plan the nuts will be glued in place on the other side of the hole.
 
Maybe there are no nuts just a tapped plate glassed in place - depends on how it was put together in the first place.
 
Thanks for the tips, I looked at the rivnuts but I am worried that they won't have enough grip on the rear of the grp wall and may just rip out under stress. Im sure you know the amount of stress that can be inflicted by a helpfull person fending you off by pushing the top of the stanchion. also I was in B&Q today looking at a can of expanding foam thinking just that about filling the cavity.
Anyway, I have decided to bite the bullet and cut a small access hole from below and access the nuts that way. It's a pain, but it will allow me to fit a new backplate with nuts welded on which can be epoxied in place.
Hopefully the next owner in 15 years time will thank me.
 
Taking care ...

If you are careful enough in the cutting of the access - it is possible to re-use the cut-outs suitably cleaned up edges etc. as "small access" doors to the areas again. Trimming and doing a little cosmetics can make it so that it is not so dramatic an action - with the advantage of access later ....
 
Re: Taking care ...

Yes, thanks for that, funnilly enough I came to exactly the same conclusion today, I have been thinking of making a feature/selling point out of it. I was thinking of making little hinges at one end, or putting a larger backing plate on the fibreglass I cut out so, it could sit on the cutout , held in with a light glue. Any tips on cutting out fiberglass in a tight spot, most of the stanchions (12 in all) are at the top of small lockers. I did one yesterday , about 3" by 1.5" using a cutting disk on a dremmel, not too bad, but it took about 8 discs to do it. I'm tempted to design a cutting tool about the size of an egg with a cutting disk that just protudes out the end, I bet I could sell one to every grp boat owner :-)
 
Re: Taking care ...

What about a hole cutter .... shorten the centre drill a bit ...

The centre hole can then be used for a 1/4 turn lock pin ... or similar .... even a screw with nice cosmetic head through to a wood block behind ?

Surely a hole saw would be better than a dremel disc cutter .... that GRP is tough stuff to cut ...
 
Hi stardust.

I'm currently undertaking a similar task. but I'm fixing to my coachroof which has an internal lining. I can't cut acess hatches cos of the shape of the lining and I've got strengtheners which I can't tell exactly where they are. So I planned to fill an area of the cavity with thick epoxy mix and bolt right throught the lot.

This is possible in my case cos the areas horizontal mor or less dunno if this is an option for you. Builders foam sets quite hard but never tried it to fill out a void to fix thru so I dunno if this would be an option but probably would be with a decent sized backing plate, others may know.

The strongest inaccessible cavity fixing I've ever seen is the "gravity toggle" type but the fixing is only as strong as the material it's relying on. The version I'm aware of is made by Fischer Fixings, part no KD. An A4 version is likely to be available but you'll have to buy a few as they'll probably be a special from yoiu local fixing stockist, and I know for a fact they not cheap even in yellow plated.

cheers
 
Nothing terribly useful to add, alas, but I have to say that this is a very good thread. Far more novel / interesting ideas per post than most. For me it's certainly triggered some ideas for tackling one of my "impossible" access issues ... Etap owners will understand ...
 
Thanks again for the suggestions, I will hunt out the dremel steel cutting disk as the basic cutting wheels are so flimsy. They do slice through the GRP like butter, however just the slightest twist will snap the disk, and when upside down/back to front, with poor visibility, dust spraying out and elbow and shoulder joints screaming, it's sometimes hard to keep that straight line going.
I didnt understand the point about the hole cutter, perhaps if I include a picture of my problem.
[image]http://www.lady-stardust.no-ip.org/misc.htm[/image]
The section under the cap rail is sealed below with 2-3 layers of fiberglass mat, underneath the headlining, making a box section, and the nuts holding the side screws into the verical wall of this are not secured in any way.
After much reflection, I think the best approach is to remedy the initial design flaw and make these bolts pernamently accessable, so access holes have to be the way forward.
 
[ QUOTE ]
..they have 2 aditional bolts on a horizontal supporting strut that bolts to the inside face of the bulwark.

[/ QUOTE ]

Looking at your piccy. I reckon you'll be able to get away with self tappers for those two fixings as long as the stanchion base is bolted thru with a backing plate.

They may well even be s/tappers in use now.

edit: as long as the fibreglass is a decent thickness.

edit 2: Hey! I've just looked at your webby front page and I think you're on the row next to me at liverpool marina - small world hey. /forums/images/graemlins/smile.gif

Nice looking boat btw.
 
Pics

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