# Waterline

Draft marks on a motor ship of the Lake Zurich Shipping Company

The water line is the line that results from the intersection of the water surface with the side of a floating ship. Since it changes with the loading of the ship , the shipyard defines a construction waterline ( KWL ) with an assumed weight.

The length of the waterline is decisive for the hull speed , i.e. the theoretical maximum speed of the boat in displacement travel . An old nautical rule of thumb is: Length runs . The maximum speed in knots can be approximately calculated from the length of the waterline in meters using the following formula : ${\ displaystyle L}$${\ displaystyle V _ {\ max}}$${\ displaystyle L}$

${\ displaystyle V _ {\ max} = 2 {,} 43 \ cdot {\ sqrt {L}}}$

In order to overcome this speed, a considerable amount of energy has to be expended. However, once the speed has been exceeded, the ship goes into what is known as gliding , during which the hull area that touches the water becomes smaller and the frictional resistance in the water decreases. But not every watercraft can go on plane. It is primarily dependent on the shape of the hull .