Sea Miles

[DeLam]

Noticed on the "Home" page a bit about the Cape to Rio race from Yachting World
All the distances quoted were in kilometres. I always assumed everybody
still used nautical MILES. Maybe some people are and some aren´t, that´s why accidents happen like Viki!

 

[Sybarite]

A knotty problem...

 

[ponapay]

Sailing in Finnish waters they often show speed limits in kilometers per hour. Very silly and real Finnish sailors from the Aland Islands think their government is crazy as no one uses kilometers at sea (except perhaps the French, as they invented them).

The kilometer is a mathematical unit only it has no real use in measurement terms, how the world allowed the French to get away with it I do not understand.

 

[Jacket]

Ehh? All units of distance are purely arbitary distances, and have no 'real' meaning. Sure, one nautical mile is the length of one minute of arc subtended at the equator, but so what? Degrees and minutes in themselves are just arbitary divisions of a circle.

A kilometer is just as relevent as a nautical mile, or would be if charts were re-drawn in metric format.

Having had my little rant, I think you're only winding us (or the French) up anyway, so I'll go back to my beer.

 

[Sybarite]

The French use knots too. Nobody (virtually) uses kilometres at sea.

I thought a kilometre was equal to 1/10000 of the distance from the North Pole to the Equater on a longitude running through Paris. There is therefore a logic. A yard on the other hand has beeen variously interpreted as the distance from your nose to your finger tip ( whose ?) ; the length of one stride by Edward I ( he got it recorded), the length of a pendulum necessary to complete a swing in one second and only in the 19th century was it cast in brass..

I won't get into knots which all sailors understand.

 

[vyv_cox]

I understood the same as you about the definition of the kilometre, but I have additionally been told that it was miscalculated at the time, so is in fact completely arbitrary.

 

[kingfisher]

Equator=40.000km

The equater has been set at 40.000km, so:
40.000km =360°
=21600'
1'=1Nm=1.851 km


Group of people on the pontoon: skipper is the one with the toolbox.
http://sirocco31.tripod.com

 

[JEG]

Surely the superiority of the metric system is it's connection between distance, weight & volume: one litre of water = one kilo, 1000 kilos = one tonne = 1 cubic metre of water. N'est pas?

 

[vyv_cox]

No argument with that but I thought we were talking about kilometres. Biggest problem comes with combinations of values that are not commonly used, especially when restricted to multiples of three in SI. A simple one is the measurement of capacity, where there is nothing between the litre and the cubic metre - not very convenient. When you start to use more complex values, like stress, some strange units like the megapascal need to be created because the pascal is useless - one Newton (the weight of an apple!) per square metre. Energy is even worse, where even a megajoule is still only a quarter of a kilowatt hour

 

[Guest]

What JEG says is perfectly correct but the argument to favour the kilometre is circular.
The tyrant Napoleon Bonaparte imposed this and now many (but not the Land of the Free) are obliged to use it. In the same way, the Iron Chancellor, Otto von Bismark (another invader of other countries), created the Zollverien (Customs Union) which has now grown into the EU.

 

[vyv_cox]

Re: Equator=40.000km

This is the same mistake that the French made. So a metre is correct on the equator but not in France? ;~)

 

[ALLWEATHER]

Re: Equator=40.000km

pole to equator = 10,000 km so pole to pole and back on any! line of longitude(not just one through paris) = 40,000 km. this is not the same as the equator as earth is an oblate spheroid. = 21600 nm i.e 90 x 60 x 4. however legnth of nautical mile changes depending on which latitude it is measured at as legnth on earths surface measured by distention of one degree of latitude varies due to oblate spheroid(not perfect sphere)

 

[vyv_cox]

Re: Equator=40.000km

My point precisely but in more detail. As I said originally, the measurement was incorrect.

From National Institute of Standards and Technology:
The meter had its origin in August of 1793 when the Republican Government of France decreed the unit of length to be 10-7 of the earth's quadrant passing through Paris and that the unit be called the metre. Five years later, the survey of the arc was completed and three platinum standards and several iron copies of the meter were made. Subsequent examination showed the length of the earth's quadrant had been wrongly surveyed, but instead of altering the length of the metre to maintain the 10-7 ratio, the meter was redefined as the distance between the two marks on a bar.

The metre (m) is the Si unit of length and is defined as the length of the path traveled by light in vacuum during the time interval of 1/299 792 458 of a second. This replaces the two previous definitions of the metre.

 

[Roberto]

And Coulomb + Farad!

 

[DeLam]

Sorry Chaps ,I am not arguing about which is better Imperial or Metric but
using the correct units. As far as I am aware speed (velocity) in both air and
sea enviroments is measured in Knots, where 1 Knot equals 1 nautical mile per hour. A nautical mile can be X feet or Y metres in Metric ,they are the same
distance. My beef is that is incorrect to change nautical miles to kilometres because
an NM is a measurement in its own right.
I seem to remember a Mars Space probe going wrong because of a mix up between miles and kilometres.
I see YW is now quoting Cape to Rio race distances in miles, Has this post reached their ears?

 

[vyv_cox]

No argument about that. I'm sure you are correct.

There is a long history of cockups due to conversion, or its absence, between one measurement system and another. You quote the Mars probe, at least that was only money down the drain. An air crash over India two years ago was caused by a Russian pilot's inability to convert from metres to feet. Many people died. The Hubble telescope's initial failure was the result of something similar.