Guy Capra has emailed more about his godyoto sculling oar, an update of the ro (from Japan) or yuloh (from China).
The drawing in the last post was an earlier design, Guy writes. The two parts of the godyoto are now parallel, held together by a simple clamp as shown in this rather nifty animation:
Guy writes: "Note the godyoto doesn't use any rope fastened within the boat nor anything to hold the oar on the transom, unlike the yuloh and ro. It is an easy way to scull and to learn traditional sculling, and as you pointed out it is a good wayto use a standard oar yet fit it inside the boat."
Godyoto also has its own website, with dimensions to enable people to make their own.