From Alan:
It still won't let me answer
"I wasn't very clear.
Basically the force on the oar is transmitted to the boat. Like grabbing the oar and pushing the boat forwards by hand.
So if the oar is forced forwards, this force drives the boat forwards.
So the low pressure needs to be to the fore of the blade, and the high pressure to the aft of the blade.
The forward side of the blade is therefore best curved. The forward side is the underside.
Also, forcing the oar forwards also forces it deeper into the sea, this is counteracted by the lanyard. "