If you are an experienced kayaker we use this effect all the time, especially in white water we call it ferry gliding , and allows you to cross a fast flowing river with minimum effort..,(reply>), And sometimes, if you get everything just so,  you can get away with not paddling at all - and that's a real blast! I used to assume that Ferry gliding was so called because you crossed the river. Now it seems that it might have been a reference to something a little  less obvious!"