Way to tame splayed ribs?

[Howie]

I'm just about to canvas a 1960 13' Old Town Trapper. This poor guy has had a rough life: 4 broken ribs, a few 'bruised' ribs, lots of cracked or missing planking, broken inwales and missing outwales, plus the usual rotten stems and decking. It was also without seats and center thwart and had been fiberglassed! (We're calling it 'Lucky' due to it being 13' as well as being lucky to be restored & not firewood!) Anyway, the problem I'm writing about is with its splayed ribs. Due to it spending a long time (decades?) without a center thwart the ribs have splayed open. When I replaced the inwales I did so by installing them below the old inwales then cutting off the old ones. This seems to have worked well in preserving the canoe's overall profile. But to get a reasonably rounded profile I need to use a center thwart that's 37" long. I believe the original thwart for a 13'er was around 34" or 35" because the canoe's specs specify a 36" overall width. But when I draw the sides together for a 35" thwart the canoe's profile is very straight in the center - in other words, the 2" closer distance isn't shared proportionally more than a few feet or so. So my question is, does anyone know of a way I can coax the ribs to bend equally so I can make the canoe's profile closer to spec? I mean, I could install a 35" center thwart then use twine every foot or so to pull the inwales' closer together to make a nice rounded profile, but they would spring back as soon as I removed the twine!

 

[H.E. Pennypacker]

Looks like your gunwales are broken or at least misshapen in multiple places. Putting in new inwales and outwales will really do a lot to restore the canoe's shape.

 

[Howie]

Yeah... that pic was from before I worked on it. Here's one as it is today.

Everything looks ok when I use the 37" thwart. Guess I'm being too picky, but thought I'd ask for advice.

 

[Greg Nolan]

Did you pull the sides of the canoe inward uniformly before installing the new inwales? If not, the new inwales not only preserve the overall profile, but also the width at the time they were installed.

The inwale of a 15’ canoe with a beam of 37” will be distinctly longer than the inwale of a 15’ canoe with a beam of 33” or 34”.

When you straighten a curved board to create a shallower arc, you necessarily push the ends further apart. If the ends are fixed in place so they cannot go further apart, as they will be in a canoe of fixed length (and as with inwales fully installed), when you pull the curve gunwale inward at the middle, you will be pushing other parts of the curve outward --- the ends of the fastened-down gunwale cannot move either shorter or longer, so the gunwale will reshape itself. That is why the curve becomes unfair when you pull the middle in -- that the “profile is very straight in the center” is to be expected. When you try to make the arc of the inwale shallower in the center without shortening the inwale length, the rest of the inwale will push outward.

So I think that’s why you are having a problem. If you want a narrower canoe, I think you have to remove the inwales, pull the canoe sides inward to the shape and beam you want, and then holding that narrow beam and new shape (using temporary battens?), install the inwales, which will be shorter than they now are.

 

[Howie]

I see exactly what you mean - you described the situation quite well. I did pull the old inwales to 35" when attaching the new ones, and I did pull them closer together at some distance either side of center before attaching the new ones. But if I had thought it through and seen it as you describe above I would have paid more attention to the off-center distances. Nuts. But now I think on it I remember I was much more concerned with eliminating the 'kinks' in the profile caused by the several breaks in the old inwale. Oh well, no matter - likely no one but me will ever notice it. And the wider width - albeit high above the water line - should only make it a teeny more stable. Thanks for responding.

 

[shelldrake]

Did you replace the decks Howie? If so, are the replacements the same dimensions as the originals? If the replacement deck dimension across the the widest spam is more than the designed original, you would run into a similar problem. The fair arc of the wales would require a longer thwart to maintain the shape.

Matt

 

[Howie]

Yup - they're the same: just a tad less than 45deg, say +/-22deg. Good thought though.