Slip of Wheel

The difference between the distance run by a steaming vessel and the distance that would have been covered had the propeller acted upon a solid substance, instead of a fluid; in other words, the expression slip of wheel may be understood as the lost motion of the propeller. It is usual to allow a certain number of revolutions of the propeller or paddles to the mile, and at the end of a stated time the estimated distance run by the ship, according to the number of turns made, is compared with the distance run according to observation, or by the log, and the difference is expressed as a per centum, and entered in the log book as slip of wheel. The retardation by reason of head winds, opposing currents, and head seas are counted as slip.