Sunday, June 1, 2008

Setting Sheathing & Ribs

A key moment in the model canoe build had come...time to lay the sheathing and permanently put the ribs in place. Most book sources have a cursory mention of the sheath laying and I assumed it would be quite straight forward and simple. The truth was that it was the most frustrating part of the process so far, even worse then my experience carving the gunwales.

The process typically starts with laying a piece of sheathing under the stem piece protruding along the bottom hull. Then, layering like roofing shingles, the sheathing is placed on either side of this bottom piece all the way up the sides ensuring the piece above overlaps the piece below. Along the way, the sheathing is to be held with temporary ribs (quick soaked cedar) until they are held tightly pressed by the actual ribs. All started out well, but soon the sheathing was sticking to the pine gum applied to the seams and gores on the inner hull creating an even stickier mess.

Laying sheathing down

While I tried to make the sheathing as neat and attractive as possible, the frustration with gaps appearing and sheathing falling out of place made me want to secure the sheathing with permanent ribs as soon as possible. So beginning at one end, I started laying the ribs into position. This involved tapering the rib end with a chisel shape so that the ends would tightly squeeze between the inwhale and bark. Forgot to mention that at this stage the hull had been softened with boiling water so that it would give under the pressure of the ribs. Each permanent rib was loosely jammed into position but not squeezed to vertical yet

Tapering rib ends; laying the end ribs into position

Once one end was done, I moved to the other and repeated the process. So I was left with short sheathing on either end just up to the intermediate thwarts and a large gap in the middle. Rather than using authentic scaled sheathing (which would've involved more narrow and shorter pieces), I decided to curtail my growing impatience with the process by filling in the remaining centre portion with wide, long sheathing that would be tucked under the sheathing pieces from the bow & stern. Then the ribs between the intermediate and center thwarts were positioned one at a time on either side for balance, ultimately saving the 2 ribs one either side of the centre thwart for last.

Center sheathing; laying more ribs

Eventually with all the ribs in position, I began to squeeze them tightly into vertical position. In a full scale canoe, these are pounded to vertical with a wooden mallet but I found that by pulling the ribs with my fingertips towards vertical I could wiggle and position the rib very tightly to where it could not budge. When the bark dries these things will be set into position tightly. Unfortunately, try as I might, the sheathing kept shuffling with the ribs so the end result is a rather sloppy and random sheathing look. Gidmark's book mentions that Jocko Carle also favoured this "haphazard" sheathing method, but to my eyes it does make it look a little rough.

Shifted sheathing resulting in "haphazard style" look

I also had a minor problem with 2 of the ribs. While tapering the tips, I ended up taking off too much wood from the ends so that the rib would not tightly squeeze into position. Effectively the ribs had become useless for those positions. Not wanting the the symmetry of the boat to be affected, I used one of my crappy ribstock pieces to form brand new ribs for these locations. I figured it was kind of like doing a field repair. Apparently, the most common type of damage to a birchbark canoe is not to the tough bark, but to the ribs which can snap after impact with a rock. After positioning the fresh soaked rib into position, it was allowed to dry overnight with some of the cross-braces adding extra support to the hull during the drying process.

Missing rib; Bending new rib in boiling water; In position with binders

So now that the ribs are in, the hull is much, much stronger. It was actually quite amazing to feel how this seamingly flimsy and delicate craft transformed into a rigid-hull vessel. Here are some shots with all the ribs in:

Sheathing & Ribs all set

Soon to set sail

What's left is the adding the gunwhale caps with pegs & lashing, gumming the outside of the hull, and taking her out on a maiden voyage. Should be done quite soon!


beaversss said...

Yes indeed. You have met the challenge of sheathing & rib placement and won eh.


Murat said...

Thanks Ferdy! Nothing I ever read mentioned sheathing would be so frustrating. I'd like to add that your canoes are absolutely stunning - a real inspiration for an urban, newbie builder like myself. Thanks for reading my stuff.


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