Why do boats use nautical miles and why are they different than normal miles? Couldn't you just convert it to normal miles or km?

[Bodach na mara]

I thought elephants were seconds. Or was it kangaroos?

 

[billskip]

It really is simple, but as always it's made to look complicated.

The skipper called to the navigator and asked how fast they were going, the navigator chucked a lump of lead over the blunt end with a knotted rope, he counted in seconds how many knots went out...

5 knots sir was the reply.

 

[Daydream believer]

It really is simple, but as always it's made to look complicated.

The skipper called to the navigator and asked how fast they were going, the navigator chucked a lump of lead over the blunt end with a knotted rope, he counted in seconds how many knots went out...

5 knots sir was the reply.

That was depth.& he shouted, ""By the mark- Oh f..k it -too late, we are aground" as he still had a hundred feet of knotted string in his hand.

 

[thinwater]

Just a few (maybe more than a few) years ago, when GPS was not a thing and we actually used charts, it was very handy that the minute scale on the right margin was also nautical miles. Approximate navigation could be done at a glance without looking for a scale of distance.

Until mapping goes to some system other than 360/60/60, this thread is much ado about nothing.

Of course, back in the day we would not have this thread, because the OP would have already known this, or he would not leave sight of his marina.

 

[DangerousPirate]

It still seems to go in circles. "We use nautical miles and knots based on latitudes which are a 1/60 of the earths north-south circumference because we established nautical miles and knots based on latitudes which are a 1/60 of the earths north-south circumference." Goes in circles, doesn't it?

Ignoring why it came to be in the first place, there is no real reason to have it. I think my friend made a good point there.

 

[DangerousPirate]

Just a few (maybe more than a few) years ago, when GPS was not a thing and we actually used charts, it was very handy that the minute scale on the right margin was also nautical miles. Approximate navigation could be done at a glance without looking for a scale of distance.

Until mapping goes to some system other than 360/60/60, this thread is much ado about nothing.

Of course, back in the day we would not have this thread, because the OP would have already known this, or he would not leave sight of his marina.

I am sorry, but I brought up all of the already mentioned points. I am aware of why it's useful, but the question wasn't how it makes sense but why we wouldn't abandon the knots and nautical miles in favour of kilometres.

 

[Daydream believer]

It really is simple, but as always it's made to look complicated.

The skipper called to the navigator and asked how fast they were going, the navigator chucked a lump of lead over the blunt end with a knotted rope, he counted in seconds how many knots went out...

5 knots sir was the reply.

When I had my first Stella in the 60/70s I actually made wooden board with a peg in it. I dropped that in just ahead of the stern & started my Smiths stop watch, in its rubber case ( dinghy sailors will remember those). Then when the piece of line, about 100 ft long, attached to the board went tight, I stopped the timer. A sharp pull on the line pulled the peg out so the board tipped over making it easy to pull in.
Then comparing seconds to the length of line I had made on a card I knew the speed that I was doing.
.
I do not know what the sailors of old called the plank of wood, but to answer the last line of the OP's question, ie. who used a clock and a log to measure their speed really to know how far west or east they are?== Well I suppose I did.
Hence the term "LOG"
.
And finally- A knot is a measure of speed. ie one knot being equal to one nautical mile travelled in one hour. Not a nautical mile which is a measure of distance, as suggested in the Op's post.

 

[AntarcticPilot]

I am sorry, but I brought up all of the already mentioned points. I am aware of why it's useful, but the question wasn't how it makes sense but why we wouldn't abandon the knots and nautical miles in favour of kilometres.

Because knots and Nautical miles are directly relevant to navigation, and kilometres aren't.

 

[DangerousPirate]

Because knots and Nautical miles are directly relevant to navigation, and kilometres aren't.

They are on roads? In cars? Hiking? Just not on water, it used to impractical and impossible to measure distances on sea, but that shouldn't stop us now. We just need to use kmh on boats instead of knots and we'd be able to do all our calculations, in fact, fuel calculations would be easier.

 

[AntarcticPilot]

When I had my first Stella in the 60/70s I actually made board with a peg in it. I dropped that in just ahead of the stern & started my Smiths stop watch, in its rubber case. Then when the piece of line, about 100 ft long, attached to the board went tight I stopped the timer. A sharp pull on the line pulled the peg out so the board tipped over making it easy to pull in.
Then comparing seconds to the length of line I had made on a card I knew the speed that I was doing.

That's the traditional log, as used for centuries! And the name "knot" derives from the knotted line used to trail the log. The idea was that you had a sandglass that ran for (I think) 30 seconds and counted the number of knots that were pulled off the reel after the log was trailed. It's slightly more complex - the sandglass wasn't turned until the first knot passed over the stern, to ensure the log had got beyond the turbulence immediately behind the vessel. The knots on the line were spaced so that each one corresponded to (guess what!) a nautical mile per hour. So if three knots passed astern, you were travelling at 3 knots and so on. Actually, it moight be interesting to make one up!

 

[Sandy]

I always find it funny that when walking I use kilometres as UK Ordnance Survey maps are in 1km squares, when driving I use statue miles apparently based on Roman Miles, and at sea I use nautical miles.

 

[AntarcticPilot]

They are on roads? In cars? Hiking? Just not on water, it used to impractical and impossible to measure distances on sea, but that shouldn't stop us now. We just need to use kmh on boats instead of knots and we'd be able to do all our calculations, in fact, fuel calculations would be easier.

It's not about measuring distance - it's about relating distance run to position. Nautical miles relate directly to position; kilometres don't.

 

[johnalison]

They are on roads? In cars? Hiking? Just not on water, it used to impractical and impossible to measure distances on sea, but that shouldn't stop us now. We just need to use kmh on boats instead of knots and we'd be able to do all our calculations, in fact, fuel calculations would be easier.

And we’d have to clutter up our charts with a metric grid as well as lat and long. That’s a hopeless suggestion, to put it as politely as I can.

 

[billskip]

That was depth.& he shouted, ""By the mark- Oh f..k it -too late, we are aground" as he still had a hundred feet of knotted string in his hand.

It was the original combined speed and depth log.

 

[AntarcticPilot]

I always find it funny that when walking I use kilometres as UK Ordnance Survey maps are in 1km squares, when driving I use statue miles apparently based on Roman Miles, and at sea I use nautical miles.

But the exact size of your "1 km square" actually varies significantly east and west of the OS central meridian (2° W)

 

[DangerousPirate]

It's not about measuring distance - it's about relating distance run to position. Nautical miles relate directly to position; kilometres don't.

But if you'd adjust the grid, they would?

 

[DangerousPirate]

And we’d have to clutter up our charts with a metric grid as well as lat and long. That’s a hopeless suggestion, to put it as politely as I can.

We could use the metric grid instead of lat and long

 

[thinwater]

I am sorry, but I brought up all of the already mentioned points. I am aware of why it's useful, but the question wasn't how it makes sense but why we wouldn't abandon the knots and nautical miles in favour of kilometres.

I can only suggest that you turn off your GPS and navigate with map, compass and chart. See how useful kilometers are. (face palm) IF the SI systems is so logical, ask why it was not based on the geometry of the earth? Just another arbitrary (see post 5--the French thought it was logical but measured poorly) basis, no better than any other.

I suggest going out with your friend and a chart, no GPS, and try navigating with kilometers. That should settle the debate. But as many have suggested, it's all arbitrary.

[As a US engineer, our exams often featured problems that alternated between SI and US traditional units. They all worked out the same, no problem. Sometimes SI units were easier, and sometimes traditional units are easier to work with.

 

[Farmer Piles]

I measure distance in double decker buses. Planning a trip from the Canaries to Barbados is about 426396 double decker buses. It’s is much more intuitive than 1’ of arc.

But how many football pitches, Olympic sized swimming pools or blue whales is that. And how many of those buses would it take to be as high as Nelson's Column?

We need proper calibration here!!

 

[Refueler]

A Nm is 1 minute of a great circle iirc, making it a fixed length.

No.

The earth is an oblate spheroid ... best way to describe it as a pear shape ! That means 1 minute of arc on the surface of the earth is not same distance in feet / metres or whatever unit you use in all locations.