...that Francois Vivier said that I didn't agree with. He likes the oars used in Irish currachs, like these ones. The hole in the flange goes through a thole pin, which keeps the oar nice and vertical but means you can't feather them.
Now feathering is an art and a pleasure, as well as reducing the windage on the blades on the recovery. Also, a feathered blade skims over the tips of the waves instead of clipping them and throwing water all over the crew. The old currach oars avoid that problem with slim blades that can't have much grip on the water.
And I suspect that the friction between the flange and the gunwale is quite significant and probably becomes a bit of a drag after an hour or two.
So give me rowlocks any day.
Though I must admit the currachs in the Great River Race go like stink...