{ Note: this concerns paddles as in the oars used with non-motorized
canoe/rowboat/kayak type boats.... }

My first thought is that there's not much reason a paddle blade curved
either direction (forwards or backwards relative to the stroke
direction) would matter--it sweeps the same volume either way.

At the same time though, I do know that spoon oars are considered more
efficient. The $250 carbon-fiber kayak paddle I bought has spooned
blades. Rowing sculls use spooned blades. As I shop online I see that
all the cheapest plastic rowboat oars are flat, and the more-expensive
composite and wooden ones tend to be spooned.

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I guess what I have is a "Euro"-style paddle, according to this page:
http://www.roguepaddler.com/choose2.htm

I have seen pics of Greenland-style paddles online, but I'm not sure
I've seen a wing paddle yet.

Also that page notes that the narrower straight Greenland paddles are
the best for longer-distance rowing.... and they are straight. ?:|
?
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