McAndrews had reason to feel proud if he could boast of 60 percent. Leaking steam produced no useful work, and wayward heat was the owner's cash, pumped overboard with cooling water or carried up the stack with smoke. Waste, or cotton waste , is also the English marine engineer's term for the trimmings and discarded threads produced by textile mills. Around the turn of the century this material was plentiful and inexpensive and was widely used instead of rags. A cargo ship might have a propeller with a pitch of 20 feet.
Water is fluid, however, and the flow around the propeller is altered by the shape of the hull.
Some of the water in a ship's wake is actually moving forward, and the ship may move more or less than 20 feet for each revolution of the propeller. Slip is normally stated as a percentage of distance advanced. Depending on weather and load, slip usually falls between 5 and 10 percent on modern vessels.