ll vehicles display forms of instability. On a flight to Minneapolis in the 1980s, I looked out my window to see the wingtip of the 737 describing a steady oval orbit. Evidently, the aircraft’s yaw damper was out of adjustment. As a swept-wing airplane yaws to the left, its left wing becomes effectively shorter and its right wing longer, causing a roll to the left and leading to an oscillation known as “Dutch roll.” As a deep-vee boat hull moves faster and faster across water, its chines (right and left edges) rise out of the water. Because the water’s surface isn’t perfectly smooth, an oscillation begins, called “chine walk.” The boat begins to oscillate in roll, touching its chines to the water alternately. If allowed to build up, chine walk can abruptly dig in a chine, causing the hull to dart in the opposite direction, possibly flipping over in the process.