Fixing an "A" frame to a rib

[2383]

I want to fit a stainless steel double "A" frame to a rib. The frame has near vertical mounting plates to bolt onto the transom, but also horzontal plates on the feet which need fixing to the sole of the rib. At the site of attachment of these feet the distance between the sole and the hull exterior is between 2 and 3 inches and sounds dull to percussion tapping (ie feels solid with no void present).
What is my best option to achieve a strong attachment?

 

[William_H]

Presumably you mean a gantry

to carry radio antennae radar or solar panels. I don't know much about attaching stuff to a RIB however the obvious thing is that you need to spread the load of the horizontal feet at the front mounting. Ideally you need a semi flexible plate that will conform to the RIB floor and also follow any flexing but which in itself will be stiff enough to take the pressure of the smallish SS feet. Making up plates of fibreglass of an appropriate size and shape you can have more glass near the SS feet attachment getting thinner towards the outside for some flexibility. These could then be glued onto the rubber floor. good luck olewill

 

[2383]

Thanks for this. In fact the stainless feet need to attach to the sole/floor of the rib made of solid fibreglass/plywood. There doesn't appear to be a void (to enable nuts and backing plate to be used). I wondered if Rawlnuts would be sufficient, or whether I should use slightly oversize holes in the sole/ floor, fill with epoxy, allow to harden, then drill again with the correct size hole "wetting" self tapper screws with fresh epoxy.
Matt

 

[Keith 66]

I recently refitted a gantry on a Rib, it had been bolted to the transom but the fwd legs were fitted with big self tappers.
This is very bad practice & they had ripped out.
I was able to go in from the side of the moulding with a small access & slipped a stainless steel plate in through the hole , bolted the lot up then fitted a small access hatch for possible future use.

 

[chuzzlewit]

I just drilled through the hull (masonry drill)

and used stainless bolts and washers and sealant. Best to have the heads of the bolts outside or the bolts could catch on the rubber wobble wheels.

 

[srp]

I recently refitted a gantry on a Rib, it had been bolted to the transom but the fwd legs were fitted with big self tappers.
This is very bad practice & they had ripped out.
I was able to go in from the side of the moulding with a small access & slipped a stainless steel plate in through the hole , bolted the lot up then fitted a small access hatch for possible future use.

I was thinking on similar lines, definitely need a backing plate, maybe threaded so you don't have to fiddle about with nuts and washers:

Small access hatch (eg Holt Allen circular dinghy hatch) or epoxy a plug in place to re-seal the hole.

 

[Pete7]

8 layers of epoxy resin and cloth to glass it down to the deck, final layer of epoxy on its own to give smooth finish and then decck paint over the top. Won't move, no holes and if you are a neat worker, it will look like it has always been there.

Pete

 

[dnickj]

my A frame was through bolted both to the floor ( at a point with no void ) and the transome both with backing plates - this added additional reinforcement to the transome to stop any flex there is a high degree of force created moving fast in heavy weather - do not rely on screwed in fixings

 

[2383]

Thanks for all the replies. The gist seems to be use through-bolts with backing plates, not even epoxied threaded studs in the sole.

 

[srp]

I was thinking on similar lines, definitely need a backing plate, maybe threaded so you don't have to fiddle about with nuts and washers:


Small access hatch (eg Holt Allen circular dinghy hatch) or epoxy a plug in place to re-seal the hole.

My post above was meant to show this rough sketch from my forum picture library. But the forum picture library doesn't work, at least, not for linking pictures to posts, so I put it on Flickr instead.

Can't complain I suppose, seeing as it's such a useful forum, but it seems a bit strange that such a potentially useful facility doesn't work. Or is it just me? It could easily be me....

 

[2383]

Backing plates clearly the way to go. Great pictures, thanks.