H1 Unlimited

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 type of motorboat used exclusively for racing. A unique characteristic of hydroplanes is that they only use the water they are on for propulsion and steering and 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 fraction of their hull touching the water.