# Knots **URL:** \ **Category:** Factual Questions\ **Created:** [August 11, 2001, 7:45pm UTC](https://boards.straightdope.com/t/knots/75835 "2001-08-11T19:45:58Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![insider](https://avatars.discourse-cdn.com/v4/letter/i/bbe5ce/32.png) [@insider](https://boards.straightdope.com/u/insider)\ **Post date:** [August 11, 2001, 7:45pm UTC](https://boards.straightdope.com/t/knots/75835/1 "2001-08-11T19:45:58Z")
Who developed the system of measuring the speed of boats in knots? Why are they called knots? ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [August 11, 2001, 7:59pm UTC](https://boards.straightdope.com/t/knots/75835/2 "2001-08-11T19:59:35Z")
Back in the day they used to have a big rope with knots tied at even intervals. To measure the speed, you would drop the end of the rope overboard and see how many knots were left behind in a certain amount of time. ---
**Author:** ![AbbySthrnAccent](https://avatars.discourse-cdn.com/v4/letter/a/eb9ed0/32.png) [@AbbySthrnAccent](https://boards.straightdope.com/u/AbbySthrnAccent)\ **Post date:** [August 11, 2001, 10:18pm UTC](https://boards.straightdope.com/t/knots/75835/3 "2001-08-11T22:18:24Z")
[How did the nautical speed measurement ‘knots’ originate?](http://www.madsci.org/posts/archives/apr99/923405643.Sh.q.html) Abby ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [August 12, 2001, 12:14am UTC](https://boards.straightdope.com/t/knots/75835/4 "2001-08-12T00:14:28Z")
check out the chip log on this page [http://www.boatsafe.com/kids/navigation.htm](http://www.boatsafe.com/kids/navigation.htm) if you do a search for “chip log” you will probably find many good explanations ---
**Author:** ![BlueMoonofKentucky](https://avatars.discourse-cdn.com/v4/letter/b/8dc957/32.png) [@BlueMoonofKentucky](https://boards.straightdope.com/u/BlueMoonofKentucky)\ **Post date:** [August 12, 2001, 12:38am UTC](https://boards.straightdope.com/t/knots/75835/5 "2001-08-12T00:38:19Z")
To add to the rest- A _Knot_ equals one nautical mile per hour or 1852 meters (6076.1 ft.) per hour. It is also equal to the Geographic mile (Only at the equator, it approximates the Geo mile less and less as you travel further north and south) as one minute of arc in the Latitude/Longitude scale ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [August 12, 2001, 1:10am UTC](https://boards.straightdope.com/t/knots/75835/6 "2001-08-12T01:10:07Z")
I believe the standard Nm of 1852 m equals a minute of latitude at the mid latitudes (about 45 degrees) not at the equator. A minute of longitude is never used as a unit of distance for obvious reasons/ ---
**Author:** ![BlueMoonofKentucky](https://avatars.discourse-cdn.com/v4/letter/b/8dc957/32.png) [@BlueMoonofKentucky](https://boards.straightdope.com/u/BlueMoonofKentucky)\ **Post date:** [August 12, 2001, 1:38am UTC](https://boards.straightdope.com/t/knots/75835/7 "2001-08-12T01:38:46Z")
> [@](#): > > \*Originally posted by sailor \* > \*\*I believe the standard Nm of 1852 m equals a minute of latitude at the mid latitudes (about 45 degrees) not at the equator. A minute of longitude is never used as a unit of distance for obvious reasons/ \*\* Could be, But The Geographic Mile is defined as one minute of arc at the equator, and I learned the nautical mile to equal one minute of arc at the equator only, at all other latitudes it was 1852m, and only approximated 1 min arc. Got any info to clear it up. I’d like to know if I’m mistaken. ## Two cites, I will look up more in _Chapman’s_ when I get home A Dictionary of Earth Sciences, © Oxford University Press 1999 Length of mile used in ocean navigation, equivalent to one minute (1/60°) change in latitude. It is internationally defined as being equal to 1852 metres. * * * ## [http://www.its.bldrdoc.gov/fs-1037/dir-024/\_3480.htm](http://www.its.bldrdoc.gov/fs-1037/dir-024/_3480.htm) nautical mile (nmi): A unit of distance used in navigation and based on the length of one minute of arc taken along a great circle. Note 1: Because the Earth is not a perfect sphere, various values have been assigned to the nautical mile. The value 1852 meters (6076.1 ft.) has been adopted internationally. Note 2: The nautical mile is frequently confused with the geographical mile, which is equal to 1 min of arc on the Earth’s equator (6087.15 ft.). ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [August 12, 2001, 4:55am UTC](https://boards.straightdope.com/t/knots/75835/8 "2001-08-12T04:55:49Z")
[http://www.unc.edu/~rowlett/units/](http://www.unc.edu/~rowlett/units/) defines the geographical mile as a nautical mile = 1852m A degree of latitude varies between about 59.7 to 60.3 nautical miles and so would be closest to 60 at about 45 degress of latitude. ---
**Author:** ![Dr.Lao](https://avatars.discourse-cdn.com/v4/letter/d/2bfe46/32.png) [@Dr.Lao](https://boards.straightdope.com/u/Dr.Lao)\ **Post date:** [August 12, 2001, 5:47am UTC](https://boards.straightdope.com/t/knots/75835/9 "2001-08-12T05:47:25Z")
A nautical mile is equal to a minute of a great circle. That can either be a minute of latitude (approximately, since the Earth is flattened sphere at the poles) or a minute of longitude at the equator (the equator is a great circle and the lines of longitude run perpendicular to it through 360 degrees). They are the same thing. Defining it as a minute of latitude makes more sense for sailors in the past since their sextants were far more accurate than their watches. However, defining it as a minute of longitude at the equator is more accurate since the Earth is more circular at the equator than at the poles. Now both descriptions are somewhat inaccurate since the nautical mile has been defined as exactly 1852 meters.