Why some boat bottoms are V-shaped and others are flat

   The amount of V shape in the bottom of a hull is known as deadrise.Technically, deadrise is an angle measured upward from a horizontal plane at keel level. If you stand in front of or behind a hard-chined boat and look along the hull, you will be able to judge the amount of deadrise.

    A flat-bottomed boat has a dead-rise angle of 0 degrees; a deep-V hull has about 24 degrees of deadrise. The amount of deadrise varies with the intended use of the boat. A flat-bottomed boat rises onto a plane quickly and provides a comfortable, stable ride in calm water—but it will pound heavily in rough water. A deep-V hull provides a softer ride in those conditions, but will be more reluctant to rise onto a plane. An all-purpose hull—a common compromise—has a dead-rise angle of about 15 degrees.

Deadrise is the amount of V shape in the bottom of a hull. The angle can change from midhull to stern. Here, a 65-foot Viking Sport Cruiser shows her deadrise at station 4, or about 40 percent of the hull length aft of the bow.

      Deadrise angles are not always constant along the length of the hull; they often vary progressively from mid hull to stern. The deeper V at the bow allows the hull to cut through waves more smoothly, while the flatter sections aft make for more efficient planing.