THE KNOT

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A knot is a unit of speed. It is not an System International (SI) unit. It is accepted (although discouraged) for use with the SI, since it is used around the world for maritime and aviation purposes.

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"Basic Seamanship"

## Definition

1 knot = 1 nautical mile per hour or 1852 metres per hour precisely. This is the definition used in most, if not all, modern circumstances.

## Conversions

1 knot is equivalent to:

• 0.51444 m/s

• 1.852 km/h

• 1.15 mi/h

## History

In some sailing ships, speed was measured by casting the log from the stern. The log was relatively immobile, and attached by line to a reel. Some sources suggest that knots placed at a distance of 47 feet 3 inches (14.4018 m) passed through a sailor's fingers, while another used a 28 second sandglass to time the operation. The knot count would be reported and used in the sailing master's dead reckoning and navigation. This method gives a value for the knot of 20.25 in/s, or 1851.66 m/h. The difference from the accepted value today is a bit less than 0.02%.  Because a knot is already a measure of speed, the expression "knots per hour" is a solecism. Taken literally (nautical mile/hour²), it would be a measure of acceleration.

## Terms

KTAS is "knots true airspeed", a measure of an aircraft's true airspeed through the air

KIAS is "knots indicated airspeed", meaning the airspeed shown on the airspeed indicator

KCAS is "knots calibrated airspeed", or indicated airspeed corrected for position error

KEAS is "knots equivalent airspeed", which is calibrated airspeed corrected for compressibility effects.

Every would be sailor must know his or her ropes and become familiar with some common knots, just to be able to tie up a boat to a jetty.  Then there is anchoring, then safety at sea.  There are all kinds of rope and all kinds of knots, each with a different use.  A 'Knot' is also a measure of speed in water, which gains its name from the distance between two knots of a piece of rope.