Has anyone gone into looking seriously looking at the pros/cons of the double ended SUP paddle?
It seems to me that as with kayaks, surf skis etc that the turn over rate and efficient push and pull leverage that occurs with a double ended paddle just logically has to be faster for less or equal effort?
I do find that paddling with the single SUP paddle does seem to put your shoulder which is on the opposite side to the paddle in the water, at a somewhat uncomfortable angle/position all in the attempt to exert even/equal pushing leverage to the pulling arm on the paddle side.
Is this the solution?http://www.carbonerro.com/el-doble
I still seem to think though that even with this design the last part of the paddle shaft should be angled down slightly to ensure that the actual paddle enters the water completely vertical so as to be able to pull it directly along the rail line. As you can see in the video footage of this double paddle because the shaft is straight
the paddle blade pulls through the water at probably a 30 degree angle which seems to yaw the board left and right with each stroke.
Any thoughts on this? Got me thinking about getting out the poly pipe and experimenting.
Way too long for surf... and,
When you think about it... with such a long pole, you'll get less strokes per minute than with a traditional paddle. Less strokes, less distance... less speed.
If you want entertainment, punch "double ender girls video" into a search engine. 
Well I wasn't actually going to try and paddle a board with a paddle made of poly pipe, I really just wanted to see what would have to be the angle of the shaft in order that the blade enters the water vertically with the minimum amount of angle transition between alternate stroke sides was minimized.
I think it would be far to early to be claiming that a double bladed paddle would not work for touring/racing (obviously not the best for surf) I think with some direct comparison over a 250meter straight line sprint would be the best indicator.
I also disagree that the return/recovery stroke would be slower than a single paddle because if you think about it, with a single paddle it has to be brought back to the front of the board after each stroke, then brought down to the water for the next stroke.
With a double ended paddle when you finish your initial stroke all you have to do is drop the alternative side as it is already at the front of the board, ready for the next stroke the moment the initial stroke has ceased.
