Power

Power is the transfer of energy. Therefore, P = dE/dt where dE/dt is the rate of energy transfer. Instantaneous power can be rewritten as P = (Force) (velocity). For a racing shell, all of the power comes from strokes applied by each of the rowers.

Using Equation 1 for drag, we can determine the amount of power necessary to maintain a constant velocity. Because the force applied must be equal to the resistive force
P = (Resistive force) (velocity)
P = (constant) (velocity)^3 Equation 2 (Dudhia)

Given the relationship between power and velocity (Equation 2), in order to double your velocity, you would need to provide cube times as much power.

Power = (2)^3 = 8 times more power