A PDR is 4ft wide, and conventional wisdom says oars should be 1/2 the beam, minus a bit.

I made 8ft oars with rather long paddles - 30 inches is a bit much. I like how that 6 inch bevel looks on the finished oars.

Planeing a flat spot where the paddles attach to the oars is important. They don't have to be dead straight, just sufficiently wide to give a good bonding surface for the paddle edge.