If the propeller works in a solid medium (has no slip), i.e. if the water which the
propeller “screws” itself through does not yield (i.e. if the water did not accelerate
aft), the propeller will move forward at a speed of V = p × n, where n is the
propeller’s rate of revolution, as seen in the below figure. The similar situation is
shown for a corkscrew, and because the cork is a solid material, the slip is zero and,
therefore, the cork screw always moves forward at a speed of V = p × n. However, as
the water is a fluid and does yield (i.e. accelerate aft), the propeller’s apparent speed
forward decreases with its slip and becomes equal to the ship’s speed V, and its
apparent slip can thus be expressed as p × n – V.