The World Unlimited water speed record is the officially recognised fastest speed achieved by a water-borne vehicle. The current record of 511 km/h (317 mph) was achieved in 1978.
From 1909 to 1927 the record was an unofficial listing from the organisers of powerboat races.
In 1928 the record category was officially established.
From 1930 the rules of the record stipulated that a craft must make two runs over a timed kilometre course in opposite directions, with the record being the average speed of the two runs.
The record is currently ratified by the Union Internationale Motonautique (UIM).
With an approximate fatality rate of 50%, the record is one of the sporting world's most hazardous competitions.