If maritime units of measurement leave you feeling lost at sea, now's the time to get a handle on the difference between nautical miles, land miles and knots. The international nautical mile was set forth in 1929 by the First International Hydrographic Conference in Monaco. Although it wasn't officially used in Britain until the 1970s, this seafarer's measurement has endured and is currently used in all countries for both air and sea navigation purposes.

But why does the nautical mile exist? And what's the difference between a nautical mile and a regular mile? In our latest blog, Sea Chest answers some of the most important questions related to this vital measurement for sailors.

What Is A Nautical Mile?

A nautical unit of length that, when converted into familiar land measurements, equates to 1.15078 land miles or 1.852 kilometres. The nautical mile is longer than a regular mile as it is based on the Earth's coordinates of longitude and latitude, with one nautical mile equal to one minute of latitude.

The International Hydrographic Organization use 'M' as the abbreviation for the nautical mile.

What Is The Purpose Of A Nautical Mile?

Nautical miles were developed as more of a sophisticated method for determining distance compared to visual navigation at sea. When the Earth's sphere is broken up into 360 degrees and each of the degrees is calculated as 60 minutes of time, a nautical mile is a distance measurement of one minute of latitude or 1/60th of a degree.

It is far easier and more practical to use nautical miles at sea as nautical charts use latitude and longitude. This will make chart reading and plotting faster.

Why Is A Nautical Mile Different From A Regular Mile?

Nautical miles are longer than land miles because they use degrees to determine measurements of distance on the water, which is a reliable and long-standing principle of maritime navigation. Nautical miles rely on mathematics pertaining to the Earth's circumference and to longitude and latitude - this is particularly useful on longer voyages and when marine charts are in use.

What Is The Difference Between A Nautical Mile And A Knot?

A knot is a 17th century term used to measure the speed of a sea vessel. One knot is equal to one nautical mile per hour, or roughly 1.15mph on land. Knots were traditionally determined by the use of a chip log, or common log. This navigational tool was a length of rope with evenly spaced knots tied into it and the rope end would then be tied to a piece of wood to be floated behind the boat. The rope would be allowed to freely fall into the water for a length of time before being retrieved and the tied knots on the rope were then counted to work out the speed.

Why Do Ships Use Knots Instead Of Miles Per Hour?

Knots are a unit of water speed calculated according to one nautical mile. Because of this, it is much easier to navigate with knots and nautical miles as opposed to converting them to regular MPH and KPH.

Post By Ed Mason