A wooden square-rigged ship sails across an animated, wind-swept sea beneath a soft blue sky. Sails act as airfoils rather than simple wind-catchers, which is why a well-trimmed ship can sail as close as roughly 45 degrees to the wind on each side, "tacking" in a zig-zag to make progress upwind. The hull stays afloat through Archimedes' principle: it displaces a weight of water equal to its own weight, while a deep keel below the waterline resists sideways slipping ("leeway") and lets the sails' sideways force convert into forward motion. The rolling sea beneath it is built from layered sine waves approximating real ocean swells, which typically have periods of about 8-16 seconds and heights that drive a ship's pitch (bow up/down) and roll (side to side). Historically, square-rigged ships like this one were powerful downwind but clumsy upwind, while later fore-and-aft rigs (schooners, sloops) could point much closer to the wind. Drag to orbit, scroll to zoom.