Definition
A ski-shaped planing surface mounted on the underside of a seaplane or amphibious aircraft that lifts the fuselage clear of the water as speed increases during takeoff. By raising the hull above the surface, the hydro-ski reduces water drag and allows the aircraft to accelerate to flying speed more efficiently than a conventional flying-boat hull alone.
Plain English
A flat, ski-like attachment under a water-capable aircraft that lifts it up out of the water as it speeds up, so the plane can take off with less drag.
Context Anchor
Seen in discussions of seaplanes, amphibious aircraft, and special aircraft designed to take off from or land on water.
Derivation
From 'hydro-' (Greek hydor, meaning water) and 'ski' (Norwegian, a long flat runner). Together: a water-running surface, named for its resemblance to a snow ski riding on top of the surface rather than plowing through it.
Why Pilots Care
Determines water handling performance and takeoff speeds on equipped aircraft.
Analogy
It works much like a person’s water ski: at low speed it sits in the water, but as speed increases it rides higher and skims along the surface.
Intuition Check
A hydro-ski is not a snow ski for an aircraft. In this term, hydro means water, so the device is for operating on water.
Example Sentence 1
As the seaplane gathered speed, the hydro-ski lifted the hull free of the water and the aircraft accelerated rapidly toward takeoff.
Example Sentence 2
With hydro-skis deployed the aircraft reached takeoff speed faster across the choppy surface.