A recent thread was discussing a de-laminating seat frame. Now I realize there were other factors involved here; however, there has also been threads in the past year on broken seat frames and even carry thwarts, which was a concern on our big trip in 2015 due to the heavy hauls. As I am now in the process of my first build, is there any merit for adding a layer or two of fiberglass when laminating higher stress components? Or even creating a laminated piece where it may not be needed, a carry thwart that can easily be constructed from a single piece of wood, to gain strength?
Lamination, if done correctly, should add plenty of strength without glassing, but there are several other questions lurking there.
I am a big guy, tend to plonk heavily on the seat at awkward launches, and have never had a wood seat frame fail (well, once, but that was a DIY install issue with an old “repaired” seat). What has failed, or at least failed to meet my seat expectations over time, are inadequate wood seat drops. The flimsy drilled dowel seat hangers common on Old Town boats come to mind.
Having the seat wobbling around on too flimsy hangers is asking for trouble eventually, as things sway, grind and wear. For gunwale hung seats I much prefer the rigidity of truss style seat hangers, or at least something bigger than a freaking drilled dowel or piece of left over wood thwart.
If I cheat and use less than a full truss I at least use a wedge shape, \_/, usually 3 inches long at the top under-inwale end, which is where stuff starts to rot first, and seat frame width at the bottom. Those wedge shaped hangers also have the benefit of being easier to make, drill and install than a more precision fussy full truss.
All of the broken yokes and thwarts I have repaired have come from one or two root causes, or a combination of both.
Cause 1. Rotted butt ends. A lot of manufacturers slap minimal coats of varnish on yokes and thwarts. The open grain butt end absolutely
drinks in the first coat or two of varnish. Beyond poorly sealed I have taken yokes and thwarts out of new canoes for outfitting/retrofitting purposes and found, surprise, zero varnish on the ends, just a raw cut. (And surprisingly often, poorly drilled holes, see #2 below)
Darkened/blackened wood creeping out from under the inwale is a bad, bad sign on older unattended canoes. Multiple seal coats are necessary to protect those prone-to-rot butt ends. I don’t count on the manufacturer to have done due diligence, or any diligence
Cause 1a. Canoes that have been stored at home on or too close to the ground, where a heavy rain can splash decay inducing dirt or mud up into the canoe between the ends of the brightwork and the hull. That kind of wet and dirty environment is death to wood. Most of the freebie canoes I have rebuilt were store on the ground, or at least too dang close.
I would not store a canoe less than 2 feet off the ground in outside storage. Think about how far up the tent rainfly mud is spattered after a driving rain. To that end even with inside storage I try to remember to hose blast the mudcrud out from between the butt ends, inwales and hull after an especially dirty trip.
Cause 2. Poorly drilled hole placement. I took the yoke out of a brand new 3K carbon Bell Prospector. That was a very nice, double hung contour yoke, with wide ends and two machine screws per side. Of the four screws holding that yoke in place two had essentially missed the wood, with the drilled hole lapped over the edge of the butt end, a la C|.
A third machine screw hole had a whopping 1/16 inch of wood outside the hole and the 4[SUP]th[/SUP] hole was properly located. That yoke, despite having an apparently four trusty machine screws, was held in by a mere 1/16 inch of wood on one side. (That was an ORC Bell canoe, when they were struggling with construction issues)
I now take the wood yokes and thwarts off even brand new boats to inspect the hole locations and re-seal the ends. One at a time, doesn’t take long, worth a look, might be surprised.
Maybe cause 2a. The actual shape of those butt ends, if shaped to match the hull contours, is complex. If you think about the shape on a canoe hull on the inside it is far from flat in any of several dimensions. There are as many as 3 angles/contours to match the under-inwale hull shape.
Along the keel line, even with a near amidships yoke, there is a slight ) bow to the edge of the canoe under the inwale. Even more so with a wider double hung yoke. Bow or stern thwarts have even more angle / \ as the hull tapers.
Add to that the hull surface under the inwale is often not vertical. On canoes with tumblehome the sheerline edge is canted outwards at the bottom of the brightwork location. Canoes with lots of flare are canted the other way. Ay caramba that’s a lot of angles and curves, it’s no wonder most manufacturers don’t go that extra mile.
Getting the ends shaped to best fit those hull angles helps provide enough wood at the ends for machine screws to be seated in properly positioned holes. When I make yokes or thwarts* I take the time to custom shape the ends. God bless the 1” tabletop belt sander; a little off the top, check the fit, little more, check the fit . . . .
I don’t want them squeaky flush against the hull, but I want the ends to be contoured to match the inside shape of the hull and installed a popsicle stick thickness away. Tongue depressor thickness actually; I tape a tongue depressor to hull while I am fitment shaping and sanding and pull it out when I begin to tighten the nylocks on the machine screws. I think that 1/16 inch void helps maintain some drying air gap at the rot-prone butt ends.
I really prefer a double hung yoke, with wider yoke ends and two machine screws per side, especially for bigger/heavier canoes. The wider yoke ends give me more beef to work with, and reduces the chances that a single screw hole will tear out while the canoe is bouncing on my shoulders. It also allows me to use a wider, more comfortable or contoured yoke.
A shapely cupped and contoured yoke (which is beyond my DIY’ing), with a notch for the C7 vertebrae at the back of the neck, can be a thing of beauty. The one’s Esquif used in their big RX boats fit my shoulders like a glove and were dang near a piece of art just to look at.
*OK, I don’t actually make my own yokes or thwarts anymore, although I have a dozen half finished DIY’s hanging on the shop walls. I buy yokes and thwarts (and seats) from Ed’s Canoe, shape the ends to fit and then seal the heck out of those newly shaped butt ends, which often takes 3 – 5 coats of varnish or spar urethane.
http://www.edscanoe.com/caco.html
