I've seen some beautifully carved thwarts and I wanted them to be both functional and decorative, rather than just plain horizontal braces. I managed to find some online plans from the 1948 article "Canoe from the Penobscot River" by Wendell S. Hadlock & Ernest S. Dodge reprinted on the Wooden Canoe Heritage Association's website. Using photoshop to adjust to appropriate width for my smaller hull, the patterns were traced on onto some 1-1/8" yellow birch cutoffs from previous paddles and cut out with a handsaw.
Birch cutoffs; Thwarts cut out
Following some guidelines from Adney's book, I intended on shaping to the centre thwart to 7/8" thickness tapering down to 1/4" at the tips; the intermediate thwarts would be 3/4" thick at the centre tapering to 1/4" at the tips; and the end thwarts would be 1/2" thick tapering to 1/4". All this involved some marking with the combination square and carving down with a spokeshave - skills easily adapted from making paddles.
Carving with spokeshave
In the end I was left with some decent thwart blanks whose ends will be further shaped when it comes down to mortising them into the inwales.
Sanded down; edge view
Given that yellow birch lends itself pretty well to pyrography, I thought it would be a nice personal touch to add some woodburning images to the centre thwart. I decided on a simple wildlife scene with a black bear and a bull moose confronting each other with a familiar boreal forest shoreline in the background. Who knows, maybe when it's finally installed and I take the canoe paddling, I may come across this very scene on one of my paddling trips.
Bull Moose; Black Bear
Completed centre thwart