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Statute Miles vs. Nautical Miles
Thanks to Michelle d'Aoust for a very precise and detailed answer on how to convert to/from nautical miles:
A statute mile is 5,280 feet in length.
A nautical mile is 6,076.11549... feet in length.To convert from statute to nautical miles a factor of 1.15 is generally used, even though it is not precise.
(5,280 feet X 1.15) = 6,072 feet (4.11549...feet less than 1 nautical mile).You could add 4.1 feet for each statute mile to be converted. So the new formula would be: {(5280 feet x 1.15)+ 4.1 feet} divided by 6,076.1 feet = 1 nautical mile.
To convert from nautical to statute miles: The factor 1.15 may be used, but again, it is not precise.
(6076.1 divided by 1.15) = 5,283 feet (3.565..feet more than 1 statute mile). Using a precomputed table (such as Bowditch's Table 20) will result in the more precise answers.
Comments:
For a less precise answer "Chapmans Piloting and Small Boat Handling" suggests:
statute miles x .87 = nautical miles
nautical miles x 1.15 = statute miles
As a rule of thumb, roughly 7 nautical miles equals 8 statute miles. You can convert nautical to statute by multiplying nautical miles by 8 and dividing the product by seven. To reverse the conversion, statute miles times 7, then divide by 8.
A Nautical Mile is 1/60th of a degree or one minute of latitude. Be sure you know what distance measurement is being used on the charts you are working with. There are four common measures of distance used on charts:
- Nautical miles are used on ocean and coastal waters.
- Statute miles are used for inland areas such as the Intracoastal Waterway and the Great Lakes.
- Yards are often used to define distances of a mile or less.
- Meters are being seen increasingly on U.S. charts and are used almost exclusively on Canadian and other charts of the world.
And from Alan Richard - "As a point of interest, Florida boating and marine fisheries laws still express distance in leagues, as in Jules Verne's 20,000 Leagues Under the Sea. A marine league is three nautical miles."
Capt. Matt
Related Articles:
All About Nautical Charts
Nautical Chart Reading 101
How to use Dividers and Parallel Rulers
Identifying Aids to Navigation
Regulatory MarkersAlso see the Basic Boating Safety Course
and The Coastal Navigation Course
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