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Boundary Waters:

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Boats & Gear

Boundary Waters Gear List

Bell Wildfire (Royalex)

Blackhawk Ariel

Mad River Independence (sold)

Wenonah Prism (sold)
-cane seat installation
-thwart replacement

Custom portage pads

Seat-mounted portage yoke

Outside canoe shelter

Inside canoe storage



Wenonah Prism - Thwart Replacement

August, 2009

During my last Boundary Waters trip (May, 2009) I had trouble trimming the Prism because I couldn't move the big pack forward. As this picture shows, the front edge of the pack bumped up against the thwart, resulting in a variety of generally unsatisfactory weight-shifting strategies. Many times I wished for another two inches of clearance. After discarding several unworkable options, I hit on the idea of a curved thwart. The question was how to make one. I put out feelers to several wooden canoe accessory makers but, not hearing back right away and being an impatient sort, I decided to try to make one myself. After researching methods of bending wood, I launched into the project.

The rest of this page describes the process of making and installing the thwart.

The first step was to get bendable wood that would fit where the old thwart was. I found a set of (12) 1/8" x 7/8" x 24" pieces at the local Woodcraft store, including two pieces each of six different kinds and colors of wood. I now had to figure out how to soften the wood enough to bend it, as well as how to hold the pieces while they set. My first strategy was steam-bending. I made a container for the pieces out of a piece of plastic downspout and suspended it over a teakettle, as shown in several diagrams I'd seen.

The pieces for lamination waiting to get steamed:
Open tube with laminating strips

They were held in place by a wire screen.
Screen to hold wood strips

I cut an opening for the teakettle and hung the whole contraption over the stove using a ten-pound barbell weight for counterbalance.
Tube hanging over teakettle

The top end was capped with part of an electrical tape container, which fit snugly. The condensation indicated steam.
Tube with steam

The main problem with this setup was that it was too hot for the plastic. It got pretty soft and I had to find another method.
Hot tube

The pieces of wood reminded me of linguine. I laughed too, but it worked!
Cooking pasta (1)

I had made a clamping jig using a 2 x 4 and pieces of 7/8" hardwood dowel.
Bending jig

After the first end of the wood was softened enough to bend I clamped it into the jig ... Clamping the left side

... and put it under a heat lamp to dry.
Heat lamp drying setup

It was pretty warm, and after several hours the wood was quite dry.

I cooked the other end of the "pasta" ...
Cooking pasta (2)

... and clamped it as before.
Clamping the right side

As the above picture shows, the right end turned out flatter than the left end. This was due to "springback" and was expected, but the amount of straightening surprised me. I managed to get both ends into the jig and clamped it in the middle to keep it from bowing out. I left it out in the rain overnight and the next day cooked it in a 200-degree oven for six hours. That worked pretty well.
Clamping both sides

The next step was to modify the clamping jig to provide more control over the final shape during the gluing. I attached another 2 x 4 and added more dowels as clamping points, and put waxed paper on the base of the jig to keep the glue from sticking to the wood. I used Goop® Marine Contact Adhesive and Sealant rather than epoxy in the mistaken belief that it would give me more working time. The stuff was pretty sticky to start with and got stickier by the minute. But it worked.
Big jig

I glued the first two layers together to form the outside curve and clamped them until dry. Then I discovered that the glue stuck to the waxed paper so I replaced the paper with packaging tape, which the glue didn't stick to at all. The laminations were glued up one at a time and clamped until dry. This picture shows the first three layers.

Here's the thwart with all five layers glued up, the excess glue trimmed off, and the ends cut to length. I could have made it with six layers, but with five layers it's 3/4" thick, which seems adequate.

These pictures suggest that the pieces were laid edge to edge in two parallel rows. If I had done that I would have ended up with two 7/8" wide laminations and a problem of how to keep them together, and I wasn't at all sure that edge gluing would hold them. My solution was to cut four of the 10 pieces in half lengthwise and arrange them so all the seams were covered by solid wood. The two outer layers and the middle layer consisted of two 7/8" wide strips. The other two layers had a single 7/8" strip and two 3/8" strips (rather than 7/16", thanks to the saw kerf). Those layers were arranged with the wider one in the middle and the narrower ones on the outsides. A cross-sectional view would show them arranged this way:

_____ _____
__ ______ __
_____ _____
__ ______ __
_____ _____

Final bend

The next steps were:
- selecting a suitable bracket, which turned out to be a cabinet hinge;
- fitting the brackets to the thwart;
- positioning the brackets on the boat;
- trimming the ends of the thwart to fit the gunwale; and
- coating the new thwart with two layers of epoxy.

Here's the piece that thwarted my attempts to slide the pack forward ...
Old thwart

... and here's the new thwart in its place:
New thwart

This shows the cabinet hinge bracket. I attached it to the boat with #8 screws rather than 1/8" rivets for additional strength and ease of disassembly, just in case. I also added a third screw between the two outside screws for greater rigidity at the gunwale.
Cabinet hinge bracket

The purple line is a bungee cord used to hold paddles while portaging.
New thwart

It looks like there should be plenty of clearance ...
Enough clearance?

... and there is:
Room to spare

The new thwart is plenty strong but twists a little if lifted in the middle. Lifting close to the gunwale is fine.

I'll see how it works on my next Boundary Waters trip, scheduled for September 2009 - three weeks from now.

It worked great!


The Final Word

After the Boundary Waters trip the following month I put a set of skid plates on the boat because the ends had worn through in a few places. I did a great job, black on red and quite smooth. But I sold it three years later, never having used it again. Poor thing ... it was pushed aside by a Mad River Independence, which I preferred as a tripping boat because of its better handling - which was itself pushed aside by a Blackhawk Ariel (for its handling on moving water) and a Hemlock Peregrine (for its handling on lakes). I wish the new owner many years of happy paddling and rowing.


Comments and suggestions welcome. Feel free to e-mail me.
Last updated January 18, 2017
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