Making your own oars is a very rewarding experience. Plans and step-by-step instructions are available from several sources such as WoodenBoat magazine. They recently published an article called “The Geometry of Rowing” by John C. Harris in which he gives a formula for determing oar length. Unlike other calculations, he factors in the height of the oarlock above the water, a critical measurement in boats with more freeboard.
I made two pairs of spoon blade oars, one pair at 7’6” and the other at 8’6”. The wood used was basswood, very strong for its weight, although somewhat delicate. The tips of the blades have hardwood inserts for protection.