I've done a search on the topic and have located the equation used to calculate oar length given a boat's beam. For the boat that I intend to build (beam = 5' 10") the oar lenth comes out to be 11'. I've found designs for oars up to 9' 6" but nothing for 11'. Can an I just increase the diameter of the oar an amount proportional to the increase of the length over the original design(11/9.5)? Or does anyone know of some designs for 11' oars? Thanks.