Why do ships measure speed in knots?

Answer 1

ships do have speedometers (called the pit log or just log) and they're far from useless. Also while it may be that a minute of longitude at the equator equals a nautical mile a minute of latitude equals a nautical mile everywhere. The Latitude scale is ALWAYS the one that is used to measure distance on a chart. On a chart showing a large area you want to use the latitude scale at approximately the latitude of the area you are trying to measure because of the distortion inherent in the Mercator projection which is the most common one. The other projection types are for specific uses such as great circle sailing or polar navigation. The term knots comes from the old practice of using the chip log. The chip log was a device consisting of a piece of wood (the chip) usually shaped like a piece of pie with a line attached that had knots in it at regular intervals. The chip was dropped over the side and the line allowed to pay out for a measured amount of time. When the time was up it was hauled back in as the knots were counted. The number of knots gave the speed of the vessel through the water. While it may be true that the speed over the ground or "speed made good" is different than the speed through the water this knowledge is not useless. In fact it is invaluable to the navigator. The "set and drift" or the effect of the current in speed and direction can be determined with this knowledge so that course and speed can be altered to compensate for it. More than you wanted to know but I needed to correct some of the other answers I saw. ;)

Answer 2

Knots and Nautical miles are good old navy terms. The nautical mile was based on the circumference of the earth at the equator. Since the earth is 360 degrees of longitude around, and degrees are broken into 60 so-called "minutes", that means there are 360 * 60 = 21,600 "minutes" of longitude around the earth. This was taken as the basis for the nautical mile; thus, by definition, 1 minute of longitude at the equator is equal to 1 nautical mile. So the earth is ideally, by definition, 21,600 nautical miles (and 21,600 "minutes" of longitude) in circumference at the equator. If anyone ever asks you how far is it around the earth, you can quickly do the math in your head (360 degrees * 60 minutes per degree) and answer "about 21,600 nautical miles!"

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Answer 3

The term has been around since 1500's. The term Nautical Mile or Knot are heavily used by the Navy.

Answer 4

Hahahaha although number 1 had a very thourough answer it totally missed your question (I think he was flexing his brain muscle) anyway it is tradition.Having been a yacht mechanic and having many discussions with my sailor step-dad I can tell you that naval people are fanatical about tradition,as a matter of fact the first week of boot camp for the U.S. Navy is history and tradition.It is quite interesting you should research it some more you will probably like it.I have found that I didn't know near as much as I thought when I first started working on boats.Good luck and Happy sailing.

Answer 5

Speedometers do not exist on boats because distance-made-good per time is how speed is calculated based on landmark references. If a boat has one, its useless. Speed through the water is meaningless due to slip, set, and drift. For long voyages, great-circle sailing is necessary using celestrial references; sun, moon, and stars. This requires angular measurements. Spherical geometry is used to navigate. Statute miles are planar. If a ship travels 15 minutes of arc on a great circle over one hour, then its speed is 15 kt.

Answer 6

Maybe from the old days when sailors were hung up in their rigging?