Friday, April 2, 2010

Paddle Blade Warping Problem

Michael Weiser, a reader of the blog, sent me some pics and details of a few paddles he has made. They include 2 laminated versions patterned after Adney's Attikamekw paddle plan and two Northwoods paddles (Stern and Bow). Great looking stuff.

Michael's paddle collection

A problem emerged with his Northwoods bow paddle however. Since these were carved from maple, they were significantly thinned to reduce weight. When dry, the paddle is a "picture of straightness" according to Michael, but upon contact with moisture, the blade severely warps. The paddle was made from flat sawn wood stock with a grain pattern that one would assume, would be pretty ideal for strength and flex. A closeup of the tip reveals the distinct growth rings curving upwards and contributing to the cupping at the tip however.

Grain Pattern on tip

The resultant warping when wet

In addition to discussing issues with low moisture content of the wood stock, Michael also had some other points which add to the mystery. Generally, a dense pattern of annual rings make a wood less prone to warping, but other paddles with even wider spaced annual rings don't warp as much as his paddle. In addition, the larger to radius of the growth rings (a function of the girth of the tree), the flatter the rings appear and the less warping. But Michael's impression is that others have made paddles from similar stock without warping problems.

We've been discussing the options to deal with the absorption through the end grain at the tip, including using varnish (the paddles were originally oiled), sealing with epoxy, etc. But if any other any readers have other suggestions or explanations to this mystery, please feel free to post a comment.

Michael also took the liberty of preparing some basic stats on paddle surface area to illustrate the huge size of the Stern Northwoods. See the info below:

Attikamekw 11cm wide/64cm long
Attikamekw 12cm wide/70cm long
Northwoods Bow
Grey Owl Chieftain
Grey Owl Tripper
Graham Warren's Ottertail
Graham Warren's Voyageur
Graham Warren's Traditional Beavertail
Northwoods Stern
569 cm / 88 sq in
683 cm2 / 105 sq in
798 cm2 / 123 sq in
800 cm2 / 124 sq in
820 cm2 / 127 sq in
829 cm2 / 128 sq in
895 cm2 / 138 sq in
938 cm2 / 145 sq in
966 cm2 / 149 sq in

Certainly not a paddle ideal for solo paddling, but advantageous for steering and controlling a heavily loaded tripping canoe down some deep moving water.

1 comment:

Anonymous said...

I always varnish (3 or 4 coats) the blades on my paddles, and oil the handles with many coats of tung/linseed/turpentine. I also embed a 1/2" strip of fiberglass/epoxy in the tip of each blade by sawing into the tip along it's width to the width of a hacksaw blade. I'll taper this kerf up the corners an inch or so. Then I'll widen the kerf with a triangular file until on about 1/16" wood remains on each side. The kerf is completely filled with epoxy and glass cloth fibers. The combination of varnishing the blade, and reinforcing the tip makes for a strong, warp-resistant paddle.

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