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The ribs are steam bent oak, 2" x 2 1/2" in the midships and decressing in size towards the bow and stern at 12" centers with steel bulkheads at approx. 7' apart. A tree was sourced from Westonbirt Arbouretum, grown in a field so the trunk was straight up with the pith line bang in the center and then Alistair, an old school friend and I set about cutting it into ribwood. It was about as perfect as you can get (so good that I kept two planks for a table top) and so green that it sank when we threw it in the docks to keep it wet - good job we had a tie on it!
The steam box was made of pine and can be extended using an extra box for the longer planks at a later date. An old stainless beer barrel was used as the steam generator with a big gas burner underneath with a simple flexy pipe joined to three inlets down the underside length of the box. This seems to work well but ignore all the steaming times you read in the books, half an hour per inch of thickness may be fine for small dingy ribs, pine or ash but when steaming 2 inch oak think more on the lines of 1 hour per half inch! We only had so many hours a day to work so we aimed at doing 6 per day at 3 hours steaming each and were snapping about 30%.
We then decided to cut them lengthways, steam them in and then glue them together a few days later after they'd set and dried a little. Over the 11' length the outer part of the rib was 2 1/2" longer than the inner once bent- this was how much we were trying to stretch and compress the wood bending it in one piece.
Once the yacht was under cover, she began to dry out leaving 1/4 to 1/2" gaps between all the planks and we searched and searched for any good ribs. All 98 are cracked, rotten, misshaped or brittle and have to be replaced. 10 or 15 years ago it would have been easy to patch Thordis up and keep her going but now we have to get back to basics and start building the strength back into her. From the beginning we put steel tie bars across her to start pulling her back into shape and after replacing a dozen or so ribs on each side we needed to replace one or two planks to fix them too so we could continue building up the frame. It would be nice to replace all the ribs and then replank from the bottom up but in this case it is not feasible so we will be working in a piecemeal fashion steaming some ribs, fitting a few planks and then going back to do more ribs etc. until it is finished.