Hollow outboard shaft made from two light strips and two dense strips

There is logic in making the most heavily loaded walls of the box out of strong stiff timber like Douglas or ash, and using a light timber to form the top and bottom of the box. This is how UCRC's current oars are made.

Using a denser timber for the fore and aft faces allows a thinner strip and a shallower section. For example with a 75mm x 50mm section, 10mm top and bottom walls of cedar and 8mm fore and aft walls of Douglas, the UHF is 1.3kg and the total weight is 4kg. The deflection is 79mm to keep close to the 80mm limit.

Although the whole oar is lighter and probably harder wearing, it is more trouble to get two types of timber than one, and probably not worth the bother.