Definition
The angle formed between the bottom of a seaplane float or flying boat hull and a horizontal line, measured at a cross-section of the hull. A higher deadrise angle gives a more V-shaped bottom; a lower angle gives a flatter bottom.
Plain English
How sharply the bottom of a float or boat hull is shaped like a V when you look at it from the front. A deeper V means a bigger deadrise angle; a flatter bottom means a smaller one.
Context Anchor
Seen in seaplane design, float repair, hull inspection, and discussions of how an aircraft handles on water.
Derivation
From nautical use: 'dead' here means 'flat' or 'reference line' (as in 'dead level'), and 'rise' refers to how much the hull rises from that flat reference toward the sides. The term came into aviation directly from boat-building, where the same hull-shape concept is used.
Why Pilots Care
Determines how the aircraft behaves on water during takeoff, landing, and taxiing.
Intuition Check
Deadrise angle is not a climb angle or a nose-up attitude. It is the angle of the bottom shape of a float or hull.
Example Sentence 1
The flying boat's high deadrise angle let it operate from rough open water without hammering the hull.
Example Sentence 2
Higher deadrise angles improve rough-water performance but increase drag on the step.