a water wheel consists of a large wooden or metal wheel, with a number of blades or buckets arranged on the outside rim forming the driving surface. most commonly, the wheel is mounted vertically on a horizontal axle, but the tub or norse wheel is mounted horizontally on a vertical shaft. vertical wheels can transmit power either through the axle or via a ring gear and typically drive belts or gears; horizontal wheels usually directly drive their load. a channel created for the water to follow after leaving the wheel is commonly referred to as a "tailrace."