Friday, April 17, 2009

Rib Bending Stress!

The weather warmed up to the minimum temp I felt was safe for rib bending so this critical day in the canoe's birth had arrived. The Mrs. took the camera on a day excursion with the baby into town, so no action shots unfortunately. Wouldn't have been possible in the dimly lit and steam filled garage anyway - so all these shots were taken after the fact.

The canoe was set on the building bed and positioned with some left over stakes. It was thoroughly soaked with hot water to soften up the bark. Some pieces of temporary sheathing were also laid into the hull. Not sure about the best method for heating the ribs, I rigged the steaming tube used last fall to bend temporary ribs for storing the canoe through the winter.

The ribs were collected from their soak in the lake and began to soften up under the full steam of the boiling kettle. I've read and seen various ways of bending ribs, with some books mentioning bending two at a time to minimize breakage so this was what I tried. The process didn't proceed very well as I ended up breaking 6 of the initial ribs in a row! Suddenly a flood of panic ensued and all I could think of was David Gidmark's comment that builder Jocko Carle once broke 22 ribs as part of canoe build. At this rate, I was on track to break his record!

Broken Ribs

Even though I had made 10 extra ribs, things were getting too close for comfort. So the steaming tube was dropped in favour of the more monotonous but effective technique of ladling boiling water over the ribs and bending them up one at a time. Things went much better after that with only one more rib breaking.

The soften ribs were then placed in the boat and using my feet (in neoprene paddling socks to not mark up the ribs), they were pressed into the hull and temporarily clamped. Kind of tricky footwork with the cross braces stretched across the gunwales to limit the outward force of the ribs pushing against the bark hull.

Even though the ribs were bent singly, I adopted a method of securing the ribs from Ferdy Goode's photo gallery, where the ribs were stacked two at a time and spread with a single rib brace to push them flat against the hull. These were recut pieces of the staves used earlier in the build. Despite the stressful start, the final end ribs with their extreme bend didn't break so I guess it was all in the technique.

View towards the bow; the final bow ribs in position

The ribs and temporary sheathing have stiffened up the hull nicely and the bark was weathered the tension of the outward rib force well so far. Now the ribs have to dry out in the hull for a few days before they will be cut down to the gunwale height and the real sheathing and ribs can be permanently inserted.

Ribs pairs in and waiting to dry out

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