PTSUP said..
Can any one in paddle land explain why our SUP paddles don't have a similar profile to Racing Ski/ kayak blades.
Flat surface blades for Racing Ski/Kayaks dropped out about 20 years ago.
Curved profile catches and holds water.
Simple: kayak blades enter the water on the side, SUP vertically. They are closer to canoe paddles.
We also have the "flutter" to counter: some hydrodynamically efficient designs (vertical concaves) generate too much instability ("yaw" of the blade is difficult to control with a vertical shaft)
And... all good SUP paddle blades are (subtly) curved.