: I am looking for some plans or ideas on making two short thwarts for a solo canoe.

Rod,
Traditionally thwarts have a sort of reverse hour glass shape. That is, the ends are about 2-1/2 to 3" in width. Then the width of the thwart narrows before widening out again to 2-1/2 to 3" width in the center. In plan the lower ends and center may also thicker. The design developed as the best compromise between secure fastening to the wales, weight and strength. The meat of the piece is in the center where it's needed to resist both compression snd lateral loads. The flair at the ends provides both a larger bearing surface to spread loads over more of the wales. The width provides more material for fastenings, which in traditional canoes were lashings. It also provides a longer lever along the wale to resist tortional loads.

While you may be planning on using metal fasteners, the physics are the same. I would stick with a design that's evolved over 50,000 years and avoid the closet poles. Not only is the traditional design more structurally appropriate, I think it looks better. The graceful curves are there primarilly to remove unneeded weight without creating any abrupt changes in strength which can result in a fracture, but it is hard to deny their beauty.

Get some nice hardwood and rough it out. If the curves look fair and smooth it probably what you want structurally and a chance to get in touch with a lot of builders who came before you. Good luck.