I am currently building a bent wood toboggan. I will take you through the steps to successfully make an toboggan out of ash.
Step 1: Cutting the slats
After selecting straight grained 8/4 Ash, I crosscut the piece to 72" long (Longer if you want a longer toboggan.
Then, using a thin kerf blade on the table saw, rip the slats to 5/16" thick.
Cut 8-10 slats(I used 7, but cut extra in case of breaking during bending!), depending on how wide you want your toboggan to be.