|Category||Unlimited hydroplane racing|
|Engine suppliers||Lycoming Engines|
|Drivers' champion||Andrew Tate|
|Teams' champion||Jones Racing (U-9)|
H1 Unlimited is an American Unlimited Hydroplane racing league that is sanctioned by the American Power Boat Association (APBA). Until 2009, the series was known as ABRA Unlimited Hydroplane, in turn renamed from APBA Unlimited Hydroplane in 2004. The H1 Unlimited season typically runs from July through September, consisting of five races.
A hydroplane (or hydro, or thunderboat) is a very specific type of motorboat used exclusively for racing. One of the unique characteristics about hydroplanes is that they only use the water they're on for propulsion and steering (not for flotation) - when going at full speed they are primarily held aloft by a principle of fluid dynamics known as " planing", with only a tiny fraction of their hull actually touching the water.
The unlimited hydroplane racing series was founded in 1946 when the unlimited class of boats was allowed to compete following World War II and the subsequent availability of surplus aircraft engines. It had been disbanded in 1922 in favor of the newly introduced "Gold Cup Class". 
The world's first sanctioned unlimited hydroplane race was held in 1903 at Queenstown, Ireland and was very modest by later race standards. That race was won by Dorothy Levitt, driving a 11 metres (35 ft) boat powered by a 56 kilowatts (75 hp) Napier engine, totaling an average speed of 31.43 km/h (19.53 mph). 
The boats were initially restricted to engines of a maximum of 10,240 cm3 (625 cu in), later increased to 12,000 cm3 (732 cu in). Hulls with "steps" or " shingles" on the underside were prohibited. 
One reason for the rule change was to end the domination of its star driver, Gar Wood, who had won five consecutive Gold Cups from 1917. One win in 1920 in his twin Liberty L-12 powered Miss America, averaged 113.317 km/h (70.412 mph) in the 48-kilometre (30 mi) race over a 8.0-kilometre (5 mi) course and set a race record that stood until 1946. "King Gar" had entered fifteen Gold Cup heats during those pinnacle years. He finished first twelve times and second three times. Throughout the years, only two boats showed up to challenge Miss America; one of those was piloted by George Wood, Gar's younger brother, in Miss Chicago. Another reason for the rule change was to make racing more affordable. 
In 1929, the 725 cu in (11,880 cm3) Class was introduced by the Mississippi Valley Power Boat Association (MVPBA). The majority of these boats were powered by Hispano-Suiza 8 aircraft engines or Curtiss OX-5s. These boats were popular in the Southern and Midwestern US, but did not attract the media attention that the expensive and exotic-looking Gold Cup Class counterparts had. 
The H1 Unlimited (prior to the 2009 Oryx Cup, known as ABRA Unlimited (American Boat Racing Association) since 2004 ) class is sanctioned by APBA, its governing body in North America and UIM, its international body.
Unlimited Hydroplanes are fast boats capable of more than 320 km/h (200 mph) on the straights and running average lap speeds of 209–266 km/h (130–165 mph). They are 8.5–9.1 metres (28–30 ft) in length and weigh a minimum of 3,060 kilograms (6,750 lb).
The modern turbine-powered unlimited hydroplane is derived from the 3-point prop-riding hydroplanes of the 1950s. These were the first boats to ride on a cushion of air trapped between "sponsons" mounted on the sides of the front of the boat, and the bottom half of the propeller, which were all that touched the water.
They were called "Unlimited" because they were the only class of boat racing the APBA that had no restrictions on the displacement size of their piston engines. The designation Unlimited has stayed with the class in the turbine era, even though there are restrictions on the turbine engine and its fuel.
H1 Unlimited renamed the drivers' trophy for the Unlimited legend in 2011.