Don't rudders, in fact, operate by creating drag?

A couple of years ago, while on a trip with several other kayaks, we came up with 1/2 MPH as the 'cost' of lowering the rudder into the water. Mostly they were the tall and skinny types, like what is popular now, as opposed to a more horizontal fishtail-like design.

I've always wondered since how a fishtail design would work out. The big problem with them, though, seemed to be that in waves they would be out of the water so much as to make them useless. Maybe in calmer waters... ?