: My paddle stroke with a Greenland blade, rather than pulling straight back,
: makes a curved path in the water (down and then gradually up, while
: flaring away from the hull), the feel of the water flowing over the canted
: blade is quite pronounced, and only a single vortex (whirlpool) is
: produced on exit, rather than the twin vortices often associated with a
: "drag stroke". Most tank testing of paddles has been with them
: held vertically and dragged backwards, quite a poor simulation of the path
: of a Greenland paddle in actual use. I look forward to more research being
: done on this topic.

I am not the worlds most efficient swimmer but I do notice I don't pull straight back with my hands, I let them move at a slight angle to my direction of motion.

Part of the theory explaining the efficiency of the modern wing paddle is that the paddle helps enforce a technique where the paddle blade moves away from the boat. Like you say this puts the vortices on one side of the blade and is more efficient. I have not tried a wing paddle long enough to notice this tendancy to enforce good technique, but I have tried the stroke pattern with greenland and "traditional" euro paddles and from a purely subjective standpoint it does seem to make a difference. I think most people with a fairly efficient stroke tend to either angle their blade slightly or put a little sideways motion into it, if only to get rid of the feel of flutter. Eliminating flutter is a pretty good indication that you are keeping the vortex on one edge of the blade. The diagonal path of the blade also reduces the tendancy to ventilate.

I am not sure where the point of a paddle working in pure "drag" mode turns into working into pure "wing" mode. Sculling is pretty much pure "wing", and pulling straight back with the blade perpendicular to the applied force is pure "drag". It is fairly clear that the forward stroke is quite different from sculling, but an efficient stroke is rarely a straight pull backwards either. Reality is probably some place in between regardless of the kind of paddle you use.

A kind of fun exersize is to try to move your kayak forward with a purely sculling type motion. Start with a sculling draw stroke and rotate it around so it pulls you forward without pulling your hands back along the boat. It works fairly well and shows what a purely lift or wing based stroke can accomplish.