There is a difference between rowing and sculling. In the simplest version of rowing, the blade of the oar is perpendicular to the direction of movement of boat and oar and propulsive force is achieved by simply pushing the water backwards, with little net circulation about the oar - similar to the operation of a paddlewheel steamer.
There is a better way, exploited by birds, scullers, and propeller driven craft. That way is to fly the blade through the fluid at an angle to its direction of motion, inducing circulation about it and letting Mr. Bernoulli do the driving.
Courtesy again of Mr. Tennekes.