What's the Purpose of (Millbrook) X Thwarts?

[Glenn MacGrady]

John Kazimierczyk sometimes builds his Millbrook canoes, which dominate whitewater open canoe slalom racing and also have a cult following among recreational whitewater canoeists, with X thwarts. I don't know why.



I suppose I could just try to contact him and ask him. But I thought it would be interesting for the builders and paddlers here to opine on what the structural or other benefits of X thwarts might be vs. straight thwarts. Or the detriments.

Opinions, comments, facts?

 

[Tryin']

Opinion: it is because of the added strength characteristics.

X-thwarts create two points of cross-keel shear resistance while adding longitudinal shear resistance at no penalty. It is several orders of magnitude more resistant to deformation in any direction at very little additional weight.

 

[yknpdlr]

A wood strip canoe builder I know says when he puts the straight bench seats in, after he fixes one side in place, he then stresses the other side slightly offset, and that it adds extra resistance to keep the boat from twisting lengthwise. That was well proven in a 34' voyageur that he built. When I removed and replaced seats back squarely in place without stressing them, the boat tended to act like a floppy noodle untll we fixed it.

 

[Woodpuppy]

Well it looks like it would provide resistance to twisting and the thwarts look rather slender, as in less weight than a “standard” wooden thwart. It also seems like it would be difficult to scoot over/past them to adjust load and trim. But I guess you wouldn’t be doing that in a WW boat much anyway.

 

[alsg]

There appears to be a bolt through the X thwarts where they meet? I don't imagine in that configuration that they would prevent twist. They'd simply pivot around the bolt.

 

[TimG]

Torsional rigidity. A triangle is stronger and more stable than a rectangle. The crossed thwarts don’t pivot on the screw in the middle because the screws through the gunnels hold the shape laterally, while the rest of the boat holds it vertically.
Take some shockcorded tent poles and make a square; that’s two std thwarts and gunwales. Now make a bow tie pattern and tape the cross together. Big difference, and he does it with the same amount of wood/weight.
I think Kaz is a great innovator. I’d really like to check out one of his Patriots (now called the Ashuelot with a freshly updated mold) for a solo river tripper. Anybody here tried one?