I needed a seat for the baby but wanted the sled to be able to grow with the child and when she is old enough that we could take off the seat and convert to a “speed sled”. To do this I needed to have a bit bigger structure at the back of the seat for support (actually I ran out of narrower wood since I did not have a plan to start with!). The seat will fit over the riser and sit on the reinforcement board on the ski. Using four Bolts and Wing Nuts on the inside the seat can be easily unscrewed and removed without any tools. Large washers protect the holes from wear.
A wide board is used as the Arm support, with a narrower board cut on an angle for the backrest support. Left over cross member 1 ½” x ½” board is used to attach the two (glued and screwed) along with an additional piece horizontal for the Arm rest. Not seen in the pictures are two lengths of 1” x 1” square stock screwed in the back of the seat to act as structure and provide a surface to screw in the back boards. A left over piece of the back board is used to finish off the top of the back of the seat. A ½” dowel is drilled and glued into the upper back. This is left to stick out a few inches on either side to provide push handles and give the sled a bit of a dog sled feel for fun.