laminateing Sistering ribs?

[Niander]

Hi i need to Sister some ribs
what wood is good..obviously will have to bend to the hull[and down near the bilge the bend is of course tight]
will they bend or do i need to steam?
thinking of using screws and epoxy
what wood and what thickness laminate recommended?

 

[johnlilley]

Hi there
there are many opinions on rib replacement. Sistering is commonly used but can always be visually obvious and sometimes untidy. It also creates a hard spot at the ends of the new frame.
It also puts a considerable extra amount of holes in the planking close to existing holes.
Would it not be possible to scarf new sections in, then you can use the existing puncture holes in the planking. You can use laminated timber or steam bent timber. I would personally use oak for both options. Laminations of about 6mm thick will cold bend in most cases.
If you scarf, create a scarf that is a minimum of three rivets long. Glue the scarf as well. Make the frame and lay it alongside the original before cutting the scarfs.
You can create a patern of the curve for laminating by using the outer hull shape at that point ( removing any knuckling caused by broken frames) and transfer this to a plywood sheet with blocks fitted on the curve to laminate a new frame in an easier enviroment. It is possible to laminate in position . but very messy and frustrating sometimes with strips moving around, glue everywher. etc.
Some might say merely replacing the frame with like for like will not p[revent the frame breaking again, but it depends what broke the frame, and if it is going to be repeated.
Epoxy glue is OK so is polyurethane.
Copper rivets are possibly best, but sometimes it is impossible to access the inner ends to rove properly so bronze screws would be ok here.

John Lilley

 

[2nd_apprentice]

That's exactly what I'll be doing with a vintage dinghy of mine: repair the cracked ribs by scarfing. Lloyd's scantling rules call for eight to ten ratio length of scarf to thickness. Bit unpractical though and you might get away with slightly less. Especially when using epoxy the struture will be much stronger than before AND it'll look much tidier than sistering! Personally I'd laminate thin strips but steam bending oak ribs would of course be perfectly acceptabe too. However oak won't take epoxy as well I heard.

Do look into the reason behind it though or you'll just cure the symptoms! Could be a collision damage or from amateur attempts at re-caulking the hull.

Patric

 

[Niander]

Ok i may scarf them they are mainly in the bilge anyway so wouldn't be seen ...but yea accept it would look better scarft it seems that a lot of old wooden boats have cracked ribs
mines a folkboat btw
saw the rib at a scarf angle then?
will the 6mm laminates even bend down in the tight bilge bend?