It isnt difficult to figure how much power you need to do a certain job in a given length of time. Nor is it difficult to predict what size engine or motor you need to do it. Suppose an anchor winch must raise a 6,600-pound anchor through 120 feet in 2 minutes. What must be the theoretical horsepower rating of the motor on the winch?

Theoretically, the winch would have to work at a rate of 12 horsepower to raise the anchor in 2 minutes. Of course, youve left out all friction in this problem, so the winch motor would actually have to be larger than 12 hp.

You raise planes from the hangar deck to the flight deck of a carrier on an elevator. Some place along the line, an engineer had to figure out how powerful the motor had to be to raise the elevator. Its not too tough when you know how. Allow a weight of 10 tons for the elevator and 5 tons for the plane. Suppose that you want to raise the elevator and plane 25 feet in 10 seconds and that the overall efficiency of the elevator mechanism is 70 percent. With that information you can figure what the delivery horsepower of the motor must be. Set up the formulas:

Substitute the known values in their proper places, and you have:

This is the rate at which the engine must be able to work. To be on the safe side, youd probably select a 200-horsepower auxiliary to do the job.