Knot
A knot is the standard unit of speed at sea, defined as one nautical mile per hour, or exactly 1.852 km/h or 1.15078 statute mph. The ISO symbol is kn. Cruising and top speeds on every yacht spec sheet, charter itinerary and weather forecast are quoted in knots.
What is a knot?
A knot is the unit of speed used in marine and aeronautical navigation. One knot equals one nautical mile per hour, which translates to exactly 1.852 kilometres per hour or roughly 1.15078 statute miles per hour. The ISO standard symbol is kn; kt and kts are also seen on yacht electronics.
The unit is inherited from the chip log, the speed-measuring device used aboard sailing ships from the late sixteenth century. A wedge-shaped wooden board, the chip, was thrown astern on a long line knotted at uniform intervals. As the ship moved forward, the line ran out; a crew member counted the knots that passed while a 28-second sandglass ran. The knots were spaced so that the count gave the ship's speed directly in nautical miles per hour.
The international value was fixed in 1929, when the First International Extraordinary Hydrographic Conference in Monaco settled the nautical mile at exactly 1852 metres. The knot is recognised by the BIPM as a non-SI unit accepted for continued use. Because the knot already encodes "per hour", saying "knots per hour" is incorrect.
Why it matters for yacht owners
Every speed figure that touches your yacht is quoted in knots: cruising speed, top speed in sea trials, fuel-burn curves, charter itinerary timings, weather and tide forecasts, and AIS displays.
For buyers, cruising speed in knots paired with range in nautical miles is a more honest measure of capability than top speed alone. A displacement motor yacht making 12 knots all day will out-cruise a planing yacht advertised at 28 knots top speed once fuel, sea state and noise are factored in.
Key facts
- One knot equals exactly one nautical mile per hour, 1.852 km/h, or 1.15078 statute mph.
- ISO standard symbol: kn; kt and kts also appear on yacht instruments.
- Recognised by the BIPM as a non-SI unit accepted for continued use.
- Origin: the seventeenth-century chip log, a knotted line paid out astern against a 28-second sandglass.
- Displacement motor yachts typically cruise at 10-15 knots with top speeds of 16-18 knots.
- Planing and semi-displacement yachts cruise at 18-25 knots and can reach 30-40+ knots.
- Saying "knots per hour" is incorrect, as the knot already is a speed.
- Hull speed of a displacement yacht: roughly 1.34 × √LWL (ft) in knots.
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View moreFAQ
How fast is one knot in mph and km/h?
One knot is exactly 1.852 km/h and approximately 1.15078 mph. A yacht at 12 knots is moving at about 22.2 km/h or 13.8 mph; a planing yacht at 30 knots is doing roughly 55.6 km/h or 34.5 mph.
Why is speed at sea measured in knots instead of mph?
Because the knot is tied directly to the nautical mile, which equals one minute of latitude on any chart. A vessel making 10 knots covers exactly 10 minutes of latitude per hour, so navigators read time, distance and speed off the same chart with no conversion.
How fast does a superyacht go in knots?
A displacement motor yacht cruises at 10-15 knots with top end 16-18 knots. Semi-displacement designs cruise at 15-20 and reach 25-30. Planing yachts cruise at 20-25 and can exceed 30-40 knots, at the cost of higher fuel burn and reduced range.
Where does the term "knot" come from?
From the chip log, used aboard sailing ships from the late 1500s. A weighted board was thrown astern on a knotted rope; a sailor counted how many knots slipped through his hands while a 28-second sandglass emptied. The spacing was calibrated so each knot counted equalled one nautical mile per hour.
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