Friday, May 23, 2008

Bending the Ribs

Now for the part of the build that most look on with trepidation...the initial bending of the ribs. All the readings mention making extras because of the very real possibility of some ribs breaking. Gidmark's chapter on Algonquin builder Jocko Carle mentions that Jocko once broke 22 ribs while trying to make a canoe! Given the limited amount of stock provided by the kit I was really only able to make 26 quality ribs to just fit the boat. So there was little room for error.

The process started by soaking the ribs in warm water in the tub overnight. The pic shows two bundles of ribs being weighed down with full water bottles. I had previously layed out and numbered the ribs when I had carved them a while back. They were numbered starting on either side of the centre thwart moving towards the bow - so I had 2 sets of 13 ribs bundled and soaked. The hull was quickly cleared of debris and full-length pieces of temporary sheathing were placed on the bottom and the sides. These were held in place with some scraps that were loosely bent to form "temporary ribs".

Soaking ribstock; Empty clean hull; Temporary full-length sheathing

Bending ribs needs a steady supply of boiling water. A few weeks back while cleaning out the parents' storage room, I came across a single 1000W electric stovetop and quickly took it for this project. Setting it up on the table, I had a constant pot of water on the boil that I would use to soften the ribs (two at a time) and begin the bending process.

Soaking in boiling water; Easy bending; 1st center ribs in position

As I progressed, I started marking the underside of the ribs with red permanent ink to show the approximate bending points. These would be hidden from view anyway and marking with a pencil tends to score the softened cedar at this stage. For some of the sharper bends as the ribs get closer to the bow, I used the rounded handle of the awl as a form. Things progressed smoothly between the center and intermediate thwarts and there were no problems.

Bending around awl handle

As I got closer to the sharper ends however, I ended up cracking one rib, with three ribs that had "wrinkled" severly enough that I thought they would fully crack when dried. The good news was that by then, I had realized that the long ribstock pieces could be bent off centre so as to obtain another rib from the same stock. So despite losing 4 ribs, I was able to salvage them given my shortening supply.

Wrinkled rib (replaced later); All ribs loosely in

At this stage, the loosely held ribs need to be tightly pressured into position by means of a "binder". This binder is basically two pieces of long cedar (like rough gunwales) placed inside the boat that are forced apart and down with struts - effectively pushing the ribs against the contour of the hull. The force of the binder is strong enough to rip out the lashing in the thwarts so something is needed to offset this outward pressure. Many readings tell of builders nailing temporary cross-braces right into the gunwale, but after building this thing without any metal fasteners of any kind, that seems like sacrilege. Instead, I used some scraps to make braces that would fit across the hull and latch onto the gunwales with notches.

Carved cross braces; Braces & Binder pieces in position

I re-used the temporary thwarts that had been removed from the structure by this stage for struts to stretch out the binder and force some pressure to hold the ribs in position. Now that the bending of the ribs was done, I took the pot of boiling water to the bathroom, placed the canoe in the tub, and poured the hot water gently over the all the components in the inner hull. Then back at the table, I tightly pushed the binder down and squeezed in other bits of dowel or scrap cedar in spots to further push the binder against the ribs. When I was done, the hull had transformed from a flat bottomed structure to a slightly rounded bottom, tumblehomed sided shape. And for the first time, the hull is rigid and strong.

Final soaking; Closeup of binder; Binder and braces in position

Now I need to patiently wait 2-3 days for the whole structure to dry out after which I can cut the dried ribs to their proper height and begin the final stages of the build.

Drying out

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