Bodach na mara
Well-known member
I thought elephants were seconds. Or was it kangaroos?
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?
- Thread starter DangerousPirate
- Start date
billskip
Well-known member
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.
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
Well-known member
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
Well-known member
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.
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
Active member
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.
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
Active member
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
Well-known member
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.
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AntarcticPilot
Well-known member
Because knots and Nautical miles are directly relevant to navigation, and kilometres aren't.
DangerousPirate
Active member
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
Well-known member
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
Well-known member
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
Well-known member
It's not about measuring distance - it's about relating distance run to position. Nautical miles relate directly to position; kilometres don't.
johnalison
Well-known member
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
Well-known member
It was the original combined speed and depth log.
AntarcticPilot
Well-known member
But the exact size of your "1 km square" actually varies significantly east and west of the OS central meridian (2° W)
DangerousPirate
Active member
But if you'd adjust the grid, they would?
DangerousPirate
Active member
We could use the metric grid instead of lat and long
thinwater
Well-known member
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
Well-known member
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
Well-known member
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.