I have heard of some trying square plates, and have seen some utilizing octagon shapes. Round takes less power to rotate in water because it is not trying 4 times (square) per revolution to create a new path thru the water. That takes a bit more power. If you rotationally staggered them, it would be less power, but now you are basically back to a circle, If you get what I mean, which takes even less power, and creates more surface area.
