Knot to Foot per Hour

One nautical mile equals one arc-minute of latitude anywhere on Earth. This means that at any position, a navigator can directly read distances from a chart's latitude scale without conversion. At 60 knots, for example, you cover 1 degree of latitude per hour. No equivalent mathematical elegance exists for km/h or mph, making knots uniquely convenient for celestial and GPS-assisted navigation.

The Soviet Navy's Alfa-class submarines could sustain about 44 knots submerged. On the surface, experimental high-speed craft have gone faster: the Spirit of Australia set a water speed record of 317.6 knots (588 km/h) in 1978. Modern destroyer escorts cruise at 28–34 knots. The USS Gerald R. Ford aircraft carrier sustains over 30 knots despite displacing 100,000 tonnes.

Sailors used a "chip log" — a wooden panel attached to a rope with knots tied every 47 feet 3 inches (14.4 m). The log was thrown overboard and the rope allowed to run freely for 28 seconds (timed with a sand glass). The number of knots that passed through a sailor's hands equalled the ship's speed in nautical miles per hour. The 47-foot 3-inch spacing and 28-second interval were calculated to give a 1-to-1 ratio with the nautical mile.

"Knots per hour" is a common mistake — since a knot already means nautical miles per hour, saying "knots per hour" is like saying "miles per hour per hour," which is acceleration, not speed. The correct phrase is simply "knots" or "20 knots" not "20 knots per hour." This is a persistent error even in media reporting, as the phrase rhymes well and sounds natural.

The HSC Francisco, a high-speed catamaran ferry operating between Buenos Aires and Montevideo, reaches 58 knots (107 km/h) — the world's fastest commercial passenger vessel. Most transatlantic container ships cruise at 20–25 knots for fuel efficiency. During the Blue Riband era of ocean liner competition, ships like the SS United States set crossing records at 35+ knots in 1952, a record that still stands.

Tectonic plates move at 2–15 cm/year on average — far below even 1 ft/h. However, during episodic "slow-slip events" on faults (a kind of slow-motion earthquake), the fault face can creep at detectable rates closer to mm/day. True ft/h movement would be catastrophic — the San Andreas Fault creeping at 1 ft/h would translate to 2.4 miles/day, far exceeding any measured geological rate.

Metal extrusion (forming rods or tubes by forcing material through a die) often runs at 1–100 ft/h depending on the alloy and die profile. Some ceramic and glass fiber drawing processes operate in this range. Paper mill wet-end press sections can be as slow as 10–50 ft/h during startup. These speeds are slow enough that workers can safely observe and adjust the process manually.

Icebergs drift with ocean currents at roughly 0.5–1 km/day, equivalent to about 55–110 ft/h. Calving glaciers can lurch forward at thousands of ft/h during surge events. The famous 2017 calving of iceberg A-68 from the Larsen C ice shelf happened over a period of days — so its "speed" of separation was only a few ft/h at most.

It depends on the magnitude. 1 ft/h = 24 ft/day = 288 in/day — for something moving a few feet per hour, inches per day becomes a large awkward number. Conversely, for very slow movement (0.01 ft/h = 2.88 in/day), in/day gives a cleaner number. Engineers choose whichever unit gives a value between roughly 1 and 1,000 to minimize leading zeros.

Sea stars (starfish) move at roughly 0.06 m/min, which is about 11.8 ft/h — surprisingly fast. Coral polyps and sea anemones are essentially sessile but can contract at a few mm/min. Some fungi extend their hyphal tips at 1–4 mm/h — about 0.003–0.013 ft/h. Slime molds (Physarum polycephalum), often used in computing research, can advance at up to 4 cm/h (about 1.3 ft/h).