Ship's speed

[flirty41]

Why is a ship's speed measured in knots, as opposed miles per hour? And how fast is a knot? And why are horse races measured in furlongs, however far that is? Thanks!

[geofbob]

A knot is a speed of one nautical mile per hour; the name derives from the way sailors used to measure the speed of a ship by throwing a knotted rope over the side. A nautical mile is defined as one minute of arc of latitude (there are 60 minutes in one degree, and 360 degrees in the earth's circumference). One nautical mile is equivalent to 1.15 land miles or 6,082 feet. A furlong is 220 yards, which is 10 chains (a chain is 22 yards, the length of a cricket pitch). There are 8 furlongs (1,760 yards or 5,280 feet) in a mile. These were/are simply non-metric measurements of distance, which are still used in horse racing, because it is an activity that likes its traditions.

[Quizmonster]

Just to add a little about furlongs to Geof's excellent answer...'furlong' originated in the words 'furrow long', a furrow being the distance a ploughman moves before having to turn back on himself. In olden times, villagers shared a common field, theoretically seen as a 10-acre square. Though its size varied over the centuries, an acre now = 4,840 square yards, so 10 acres = 48,400 square yards. The square root of that = 220...ie 220 X 220 = 48,400. Hence, one 'furrow long' or 'furlong' = 220 yards.

The reason that measurement is still used in horse-racing is most probably related to the fact that furlongs always did have to do with the movement of horses, whether before a plough or under a jockey!

[flirty41]

Thank you very much, gentlemen!

[Hamish]

So is a legue a nautical term and how much is one in chains/furlongs/yards? (any one will do)

[Quizmonster]

The word 'league' came into English from Late Latin 'leuca', though it is believed to have been a Gaulish word originally. Since the 1400s it has been taken to mean 3 miles...ie 24 furlongs, 240 chains or 5,280 yards. There is a distance called a 'nautical league' which is equivalent to 3 nautical miles. I'll leave you, Hamish, to work out what that means in furlongs, chains or yards!