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Automated technical check · version 1 ·

Miles and knots: distance is not speed

A nautical mile is 1,852 metres. A knot is one nautical mile per hour.

4 min read
Manual contents
In this guide
Two unit relationships: one nautical mile, shown as M, equals 1,852 metres; one knot, shown as kn, equals one nautical mile per hour. An ideal example shows that six knots for two hours corresponds to twelve nautical miles.
Nautical mile and knot

Original schematic illustration. Read the explanation and limitations in the lesson.

insideSailOriginal insideSail artwork — all rights reserved
Enlarge the diagram
Two unit relationships: one nautical mile, shown as M, equals 1,852 metres; one knot, shown as kn, equals one nautical mile per hour. An ideal example shows that six knots for two hours corresponds to twelve nautical miles.

A number becomes clear when its unit accompanies it. “Five miles” describes distance; “five knots” describes speed. Mixing them prevents even a simple comparison. insideSail primarily uses metres for boat dimensions and knots for speed.

The relationship in numbers

1 nautical mile = 1,852 m; 1 knot = 1 nautical mile/hour

m, nautical mile, kn, h

Speed relative to what?

Two panels distinguish speed through the water, STW, from speed over the ground, SOG. The first uses the water as its reference; the second uses the ground. The caption explains that current can make the values differ. No numerical speeds are shown.
Speed relative to what?

Original schematic illustration. Read the explanation and limitations in the lesson.

insideSailOriginal insideSail artwork — all rights reserved
Enlarge the diagram
Two panels distinguish speed through the water, STW, from speed over the ground, SOG. The first uses the water as its reference; the second uses the ground. The caption explains that current can make the values differ. No numerical speeds are shown.

Speed through the water and speed over the ground use different references. On a display, STW commonly means speed through water and SOG means speed over ground. Both can use knots. A shared unit does not mean an identical measurement, and the terms alone do not identify sensor method or quality.

When reading a performance description, look for units, reference and conditions. An owner’s observed speed should remain labelled as an observation rather than automatically replacing model data. The multiplication example assumes constant speed; acceleration, pauses and changing conditions are outside that exercise.

Concepts in this lesson

Knot — speed

A speed unit: one nautical mile per hour. Distinct from a rope knot.

Nautical mile

A distance unit equal to 1,852 metres.

Sources and references

  1. C-51 — A Manual on Technical Aspects of UNCLOS (TALOS) ↗

    International Hydrographic Organization · Edition 6.0.0, May 2020 · Chapter 3 §§3.6.1, 3.11.2: international nautical mile

    Version: Edition 6.0.0, May 2020. Jurisdiction: International. Used solely for distance-unit definition, not maritime-boundary advice.

    Checked on
  2. MGN 379 (M+F) Amendment 1 — electronic navigational aids ↗

    Maritime and Coastguard Agency · Amendment 1 · Course and speed over ground / through the water terminology

    Version: Amendment 1. Jurisdiction: United Kingdom. Terminology only; operational radar and collision advice not reproduced.

    Checked on

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