trev
New member
But of what possible use is it ?
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<hr width=100% size=1>Trev
Admiralty Nautical Mile
- Thread starter MainlySteam
- Start date
BrendanS
Well-known member
It's not a case of what use it is, but use it was. As John says, do a search and you'll find it was a commonly used measurement, and many countries had their own definitions of many commonly used nautical measurements - eg example given here <A target="_blank" HREF=http://www.hemyockcastle.co.uk/nautical.htm>http://www.hemyockcastle.co.uk/nautical.htm</A>
the Nautical Mile is defined as the length of 1 minute of arc along a meridian, but the Earth is not a perfect sphere. Therefore 1 minute will be equal to 6046 feet at the Equator and 6108 feet at the Pole. The average is 6077 feet, which was rounded off to 6080 feet by the British Admiralty.
In 1929, the International Nautical Mile was defined as 1852 meters exactly (which brings us closer to the original average.) The United States adopted it in 1954.
Everyone seems to be missing the point entirely of John's original question, which was not what is the definition of a nautical mile, but who originated the Admiralty nautical mile
John,
I suspect, having done a good trawl, it wasn't a case of one person taking the decision, but a departmental decision, as that is how the Admiraltiy worked.
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the Nautical Mile is defined as the length of 1 minute of arc along a meridian, but the Earth is not a perfect sphere. Therefore 1 minute will be equal to 6046 feet at the Equator and 6108 feet at the Pole. The average is 6077 feet, which was rounded off to 6080 feet by the British Admiralty.
In 1929, the International Nautical Mile was defined as 1852 meters exactly (which brings us closer to the original average.) The United States adopted it in 1954.
Everyone seems to be missing the point entirely of John's original question, which was not what is the definition of a nautical mile, but who originated the Admiralty nautical mile
John,
I suspect, having done a good trawl, it wasn't a case of one person taking the decision, but a departmental decision, as that is how the Admiraltiy worked.
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MainlySteam
New member
Re: Extract from Web ....
Big smile for you Nigel /forums/images/icons/smile.gif - I suspect what you say is accurate and what you say about the NM certainly is.
Like you I tend to think in NM and 1/10ths of a NM (cable) in so far as distances are concerned but as I said in an earlier post with depths in meters I do a calculation from metres to decimals of a NM when determining swinging radius for the length of anchor cable veered. As I said my anchor watch also works in decimals of a NM (what method it uses for determining NM from the change in Lat/Long triangle I do not know but is of no consequence for my purpose).
In the end the small difference between the old 6080 feet and the international 1852 meters for everyday purposes is irrelevant (I said earlier that I used to just round the 1852 to 1850) but, contrary to what at one poster seems to think that is not the point of my original question - I was interested in the "who and when" history of the Admiralty NM which seems to be unknown to us.
Thanks for your constructive feedback Nigel, your last post was very interesting, especially the fathom, cable and shackle parts.
Thanks to all
John
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Big smile for you Nigel /forums/images/icons/smile.gif - I suspect what you say is accurate and what you say about the NM certainly is.
Like you I tend to think in NM and 1/10ths of a NM (cable) in so far as distances are concerned but as I said in an earlier post with depths in meters I do a calculation from metres to decimals of a NM when determining swinging radius for the length of anchor cable veered. As I said my anchor watch also works in decimals of a NM (what method it uses for determining NM from the change in Lat/Long triangle I do not know but is of no consequence for my purpose).
In the end the small difference between the old 6080 feet and the international 1852 meters for everyday purposes is irrelevant (I said earlier that I used to just round the 1852 to 1850) but, contrary to what at one poster seems to think that is not the point of my original question - I was interested in the "who and when" history of the Admiralty NM which seems to be unknown to us.
Thanks for your constructive feedback Nigel, your last post was very interesting, especially the fathom, cable and shackle parts.
Thanks to all
John
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MainlySteam
New member
I suspect you are correct Brendan and as you will have realised I have done a lot of trawling too without much success (might account for Google's listing success).
For the "when" bit it must have been in relatively recent centuries (maybe after Cook - perhaps 19th Century?) as I assume that the diameter of the earth was quite well known when the quite accurate 6080 feet was decided upon.
Regards
John
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For the "when" bit it must have been in relatively recent centuries (maybe after Cook - perhaps 19th Century?) as I assume that the diameter of the earth was quite well known when the quite accurate 6080 feet was decided upon.
Regards
John
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BrendanS
Well-known member
Came across a few sites that suggested that the Admiralty nm came from the fact that that would correlate to the latitude of the UK
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tome
New member
John
Interesting question - I'll see if I can unearth anything on the history.
Regards
Tom
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Interesting question - I'll see if I can unearth anything on the history.
Regards
Tom
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tome
New member
Trev
You are confusing a flat projection with metric measurements in Eastings and Northings with a spherical datum from which a nautical mile has been derived based on a mean minute of arc. The question is when and how the Admiralty version was derived.
As well as being confused, you could do with brushing up on your manners. It was an interesting question and the only B*ll*cks I can see here appear in your post.
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You are confusing a flat projection with metric measurements in Eastings and Northings with a spherical datum from which a nautical mile has been derived based on a mean minute of arc. The question is when and how the Admiralty version was derived.
As well as being confused, you could do with brushing up on your manners. It was an interesting question and the only B*ll*cks I can see here appear in your post.
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MainlySteam
New member
Thanks Tom. I had you in mind as someone who possibly knew or could find out.
John
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John
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