I get frequently asked why I paddle my open canoe, Iki Wa’a, with a double blade. Well traditionally this size of canoe (12’ x 30”) would always had a double blade (from its western origins I presume).
When I built him (thought clearly not from the Pacific Ocean it has a Polynesian name where boats are male) I tried the single paddle but just couldn’t get in a low enough position to feel the canoe was stable. I have an ankle injury and kneeling is hard and kneeling low painful. All the result a a skateboard crash but that’s a different story.
So sitting low was simply more stable. He has a max beam of 30 inches, with some tumblehome and if it was any wider my knuckles would hit the gunwale.
That I think is probably the true answer once the canoe becomes bigger it is simply is too wide to use a double blade. That said in addition to beam: seat hight, freeboard and paddle length are all factors.
Given my time again, firstly wouldn’t have bought the skateboard that resulted in the ankle issues, secondly Iki Wa’a would perhaps have a little more weather line beam and a little less freeboard. At the end of the day the single blade is very much more graceful.