The thrust obtainable from a propeller depends on three variable quantities :

1. (1) The revolutions per second (n).

2. (2) The dimensions of the propeller.

3. (3) The slip (s).

Two further quantities are involved, the Torque (M) and the Power (H), but these are both dependent on the three preceding.

Assuming, in the first place, a constant slip (say, 100 per cent.), and choosing any convenient vaiue for the revolutions, we immediately fix a relation between the power consumed and the torque.