That pretty much covers it. Wouldn’t 500 miles on land be the same as on sea when measuring any travel across the globe? If you want to explain knots versus mph as well I’m willing to learn.
A nautical mile more or less started out as being equal to a minute of latitude. That makes it equal to about 6080 feet, or a little more than 10% larger than a regular (statute) mile. The reason was that it was easier to keep track of on a map where the linear scale wasn’t constant, like a Mercator nautical chart. No matter where you were on the map, one degree of latitude was always 60 nautical miles. So it was commonly used in shipping and later in aviation. It’s still being used to this day. The military aviation weather office I used to work in still measured official wind speeds in knots.
Correspondingly, a knot - or nautical mile per hour - is a little more than 10% larger than a regular mile per hour.
Nautical miles are longer, for whatever historical reason, that’s all. There’s no reason why we couldn’t measure sea trips in statute miles but it wasn’t and isn’t done that way.
A “knot” is just a nautical mile per hour, and your speed in knots used to be measured with a log line. That was a rope with knots every however-many yards - you threw one end of it with a draggy hunk of wood attached over the side while your colleague started a small sand-glass and counted how many knots were pulled through your fingers until he said “Stop”. By a simple piece of arithmetic over the spacing of the knots and the duration of the sand glass, your speed in knots was the number of knots that had run through your fingers.
I once leafed through a 17th century encyclopedia and most every European country had its own basic measurement called mile, at least the terms were translated as mile in English.
FWIW, In Norway and Sweden a mile means ten kilometers.
Wacky Scandinavians. Thanks for the info everyone!
The difference is actually 15%. To be precise, 1 nautical mile = 1.15078 statute miles.
According to Wiki, the glass had a duration of 28 seconds and the knots were spaced 47 ft 3 in apart.
As that article shows, the piece of wood at the end of the line had a rather sophisticated shape.
cool!
didn’t know that.
To be precise, “mil” is a metric unit in common but not official use, of 10 kilometers, based on the old Swedish and Norwegian landmil (land mile) units that were close to that (but different).
nautisk mil (nautical mile) is a unit of 1852 m
sjømil (sea mile) is sometimes used for nautical mile, but this is considered erroneous by the pedantic, since the last official definition of sjømil was 7408 m or four nautical miles, which is why nautical miles were called kvartmil (quarter miles).
To quote the great Jack Aubrey - “A nautical mile is somewhat longer, and very much wetter! Ha ha ha ha!”
If you look at charts used by boaters they commonly do not have a specific scale on them like maps for land based uses. The user of the boating maps know to pick up the scale from the longitude markings.
I always thought it sort of a shame that kilometers and nautical miles couldn’t have an easier conversion constant. The both started out as a subdivision of the circumference of the earth. But I guess the metric guys wanted to get away from all that old school 60 and 360 nonsense.
One reason for this is that on Mercator projection charts, the length of a mile on the chart varies depending on where (specifically at what latitude) on the chart you are looking.
It’s not much of an issue for large scale charts covering local areas, and those will commonly have a scale on them. However, for small scale charts covering large sections of ocean, the length of a mile can vary considerably, and you have to pick it off from the latitude scale.
And the dog watch is cur-tailed.
That actually belongs to Stephen Maturin - though JA was indeed fond of repeating it.
According to
It is 57,875/50,292 or ~1.1507794480235425117314881094409
Brian
I don’t think that’s carried to sufficient decimal places to convey just how much it is not 1.15078. :dubious:
So that’s “approximately” as in “to a far higher degree of accuracy than a thousandth of an inch per light-year”, then.
The statute mile comes from the Roman ‘millia passum’ = 1 thousand steps.
It was the measure of 1000 double steps (counted each time the left foot touches the ground) of a Roman legionaire.