KILO

A jet hydroplane on a glass-calm mountain lake at dawn. A water speed record is not one run — it is two passes through the same measured kilometre, one in each direction, inside a single five-minute attempt window, and the mark is the average of the two. The standing outright record is 511.11 km/h, set in 1978 and never beaten since. Beat it.

How to play

• W/S (or ↑/↓) throttle lever · A/D steer · Q/E trim nose-down / nose-up · Space drag chute · C camera · R new attempt · P pause. Keyboard alone is enough; full touch controls on mobile.
• Hold full throttle to break over the hump at about 95 km/h — below it the water holds the hull like glue, above it the boat unsticks onto the plane.
• Above 350 the hull goes light: aerodynamic lift under the hull is getting ahead of the centre of gravity, and the boat is riding on centimetres of wetted surface. Trim nose-down or she blows over near 440. Trim too far and she spears a sponson in at 11 g. The record lives in a sliver of trim between the two.
• Cross the kilo, pop the chute, turn round in the basin, run it back the other way. Both passes inside the window and you have an official two-way mark. Any average at all gets you on the board; 511.12 makes history.

The twist

The lake remembers. Your outbound pass lays down a real, persistent wake — crest lines that spread outward and settle over two or three minutes — and it is still out there when you come back through the kilo at 500+. Chop that would be nothing at taxi speed will pitch a prop-riding boat clean off the water. So every attempt is the same three-way bargain: ease off the outbound pass, offset your return line inside the 60-metre gate, or sit there watching your own wash flatten while the attempt window burns.

How it was made

Dropped in one autonomous run: the concept and every word here came from the routine; the simulation — a quaternion rigid body at 120 Hz, three planing contact points, a genuine displacement-to-planing drag hump, underhull aero with the centre of pressure ahead of the CG, and the decaying wake-field ring — was built and numerically tuned by a Claude Opus subagent against a headless test harness, then verified live in a browser: an untrimmed full-throttle run blew over at 441 km/h, within 6 km/h of what the harness predicted, and a cautious 78%-throttle run posted an official 393.80 km/h pass. No assets, no CDNs — one HTML file and a vendored three.js.