Colin,

The methodes do not chance when using a different unit. A 2,207 lbs carton of milk is handled exactly the same way as a 1 kg cartons of milk which is handled the same as a 1 liter carton of milk.

So I really don't see why using nm is more "convenient" than another unit. Afterall the distances between longitudal lines isn't constant as well so how handy is nm here. Also a change of the distance between latitudal lines can easily be expressed by any other unit. One could even change the distance between these lines to reflect say 100 km.

Actually, lately more and more systems are in use where the position is given by a short code that is referenced to a series of square block along a given longitudal line. What issue is there to make these block say 100 x 100 km or even 10 x 10 km or any other measure. As you say inside these blocks a mercator projects is practical and sufficiently accurate.

Why do we have to devide the globe of the earth in to 1/60 and 1/360 parts ? For decades now landsurveyers have used a 400 degree system to measurement angles and distances because that is more practical than 360 degrees. A change of reference like that can easily be made in global navigation as well. Why not devide angles in portions of 10 ? Subdevide these another 10 portions each and so on. Much easier to use than 1/360 then 1/60 again 1/60. And the methodes of navigation won't change.

No seriously, the use of nautical miles is tradition based. That is all. When I navigate I only use the degree system. Hell I find it more easy to just express my speed in bow seconds or bow minutes per hour or day. I don't even do nm conversions.

They only conversion I do regulary, but for other reasons, is m/s and knots (and back) just because the conversion is so simple. 1 m/s = 1.9438 knots. = say 2 knot with a 3 % error. So if I'm travelling at 20 knots ; I know immediately that I'm doing just better than 10 m/s (actually 10.3 m/s). That is a speed measure I can directly relate to wether I'm on land or water. On my 5 mtr long cat it means two boats lengths travelled per second. Now do the same using nautical miles and a 16'2" long hull. I wish you alot of fun dividing the numbers by 6076.12 (= feet per nm) and 12 (inches per feet)

Wouter