Screwing into thin GRP (without subsequent tear out)

[JumbleDuck]

I had thought about creating a lumps of thickened epoxy to drill into for the screws (have been watching too much Sail Life). However, I assumed there was no way to access the void behind the inner liner. However, on reflection of your post, I could always take out the entire hatch frame and see if this gives me the access I need between the inner skin and the hull.

Epoxy putty is my favourite stuff. It's basically very sticky blu-tak which sets. However, if you can get access it might also be worth trying to stick in wooden backing pads or strips.

 

[rogerthebodger]

Hmmm, ferrocement, whatever happened to its popularity?

It lost popularity because pre molded GRP hulls became available colvic Colvic and the like.

Production of molded boat became more economic due to semi mass production methods and economies of scale.

People became more affluent so started to buy more finished boats so less people would DIY

A Ferrocement hull wese cheep to make but the fitting out costs were the same as any other boat so lots of ferrocement hulls were built but few finished as the builder ran out of money or enthusiasm.

Like a lot of reinforced cement structures the internal steel was not protected correctly and started to cause the concrete split and breakaway.

This happened in the bull ring area of Birmingham which was rebuilt mainly with reinforced concrete.

Design and especially the reinforcing is better protected these days and the epoxy sealing is also better but the labour cost is still higher, unless DIY , than a per molded GRP hull.

 

[salar]

I had thought about creating a lumps of thickened epoxy to drill into for the screws (have been watching too much Sail Life). However, I assumed there was no way to access the void behind the inner liner. However, on reflection of your post, I could always take out the entire hatch frame and see if this gives me the access I need between the inner skin and the hull.

If you can, simply slip in a piece of ply behind the skin and stick in place with Sikaflex or equivilent. Then you can screw into that. I have done this where I have access to the underneath where bolting isn't practical.

 

[rogerthebodger]

Seems like a good idea, but these magnets tend to rust. I used some to secure blinds on my companionway doors, and they've rusted quite badly.

I use that method to hold up electrical access panels in the ceiling or my steel boat.

This worked where velcro did not as the glue on the velcro failed in the tropical heat inside the cabin when we were away.

 

[alahol2]

I have a similar problem. I have to screw rowlock sockets to the double-skinned gunwale of a Bobbin dinghy with no possible access to the back. One rowlock pulled out on the very first stroke because, it turns out, the skin is thin and slightly split. Plan B failed completely, because it turns out that Sikaflex doesn't stick, even slightly, to plastic rowlock sockets.

Been there, done that (on a Bobbin). Drop a piece of string/wire through the hole from the top. Catch it inside the hull and tie on a piece of 1" x 1" (IIRC) slathered with CT1/Sikaflex. Pull it up inside the double skin with the string. Wait for the gunge to go off. Drill and screw your sockets into the wood.