Knot (unit of speed)

A knot (abbreviated as kn or kt) is a non-SI unit of speed equal to one nautical mile per hour, defined precisely as 1.852 kilometers per hour (approximately 0.514 meters per second).

It is essential to distinguish the homonym: a knot as a measure of velocity versus a knot tied in a line (such as a bowline or clove hitch). The speed unit historically derives from counting knots tied at regular intervals on a log line cast overboard to determine a vessel's speed through the water.

In modern seamanship, navigators monitor two distinct speed parameters expressed in knots: Speed Through Water (STW), measured by a paddlewheel log, and Speed Over Ground (SOG), derived from satellite positioning systems. Integrating data from GPS and electronic navigation allows the skipper to account for set and drift caused by currents and leeway. Comparing these speed vector metrics alongside headings from a marine compass is fundamental for dead reckoning. According to Wikipedia's entry on speed sailing, officially recording maximum craft velocities requires strict measurement protocols managed by governing bodies like the WSSRC.

Calculating navigation distance is straightforward with knots: traveling at 6 knots for 2 hours yields exactly 12 nautical miles.