See this discussion on oars/sculls and levers. The rower pulls the scull at the handle. The scull rotates around the oarlock. The blade seems to be at a fixed point in the water, but in reality it slips slightly. The force on the blade is given by:
The sculls are at an angle with respect to the axis perpendicular to the boat. The resulting blade velocity in the water has two components, a component because of the boat velocity, and a component due to the angular velocity of the scull.
The blade/water interaction results in drag and lift forces on the blade. The basic equations are explained nicely by Marinus van Holst, so I will just give a summary here. Basically, the harder the rower pulls, the more the blade slips. In light rowing, there is almost no slip, and the angular velocity of the scull is such that the blade remains at the same location in the water. When the rowers pull harder, this is result in a slip, such that the blade force equals .
The propulsive blade force is given by:
The lift force given by:
where A is the blade area, , the velocity component perpendicular to the scull shaft, is given by and , the component in the direction of the shaft, is given by , and the “angle of attack ” is given by .
The drag force is given by:
For , I use a value of 1.0.
Finally, one must not forget to multiply the blade force with the number of blades for the boat, considering that scullers have two blades per rower. It took me a while to figure that out …
Note 2011/04/15: Removed from the lift and drag force equations. See discussion below.