Following further discussion on the W.C.H.A. Forum it appears the ribs are most likely made oof Rock Elm. The trouble is although I have some offcuts of Elm in my workshop they are English so they just don't look right and as it happens the Oak I bent earlier is a much better match in terms of colour and grain so I have decided to proceed with that.
Now the next consideration is the tacks. Nick popped over to my workshop on Saturday and delivered the tacks he had but Unfortunately although they are the right shape and size they are brass instead of copper so won't match in looks.A minute after he left the tacks I had ordered on Sam's recommendation arrived. Here is a picture showing the selection I now have to choose from and an original one (far right).
When you look closely, you can see the subtle design of them. They have a triangular cross section that narrows near the head. The point is very fine so it will be bent over easily once it is through the timber allowing it to hold the two pieces together tightly. Some call this clinching others call it clenching you choose!
I decided to try one of my new copper tacks in the top of an existing rib where it joins the gunwale and the original one has fallen out. When I placed it in the hole and was about to nail it in I noticed the head on it was a bit bigger than those next to it.
I decided as it was only one and in quite a prominent place I would reduce the size of it's head by putting it in a drill and sanding it down.
When I fitted it the crack in the rib(that was already there) opened up a bit more but I think it will be all right as many of the others have them in just the same place and although I may fill them they certainly don't warrant rib replacement or repair.
With that done I moved on to fitting a whole new rib where I had removed the worm eaten one.
I put an Oak rib in position drilled pilot holes through it and began tacking it on. The first two tacks went fine but I thought that maybe they weren't quite long enough as I couldn't see a lot of the point on top. I decided to try one of the longer tacks and then.... the rib split!
Ok lesson learnt.
The small ones will do. I removed the split rib which showed me the tacks I had put in were actually doing their job well and was grateful that I hadn't got to the last tack before the split occurred. I continued nailing a fresh rib in place with the smaller tacks and at one point where one plank is a bit cupped I used a batten of wood pressing on the floor to help hold it tight against the rib but apart from that it was fairly straightforward.
I now had the bits at the top to trim off and used my Japanese pull saw to cut them.
I then did another one in the same area after removing another wormy rib. There are two more also in this area that I might replace but it is best to do them one at a time rather than taking four out all at once as it may distort the hull.
So that's where I shall leave if for now.
Thank you for reading and please feel free to leave comments or questions.