Metric system is a mistake at sea

Published on September 15th, 2022

The use of the metric system by the global sports league SailGP has stirred up the international sailing community, and in this report from the seaside town of Frinton on Sea along the English Channel, David Evans explains why the metric system is absurd and meaningless at sea:


So a Knot is a Nautical Mile per hour, but it is much more than that! It links us humans to our Planet in a very unique way, plus of course it is the original decimal system.

A Nautical Mile is defined as a minute of arc at the equator. So 60 X 360 = the diameter of the earth, in Nautical miles. Then 1/10th of a Nautical Mile is a Cable – and yes this term is used extensively by professional seaman throughout the world. More so…

• 1/10th of a cable is a chain.
• 1/10th of a chain is a fathom.

We are done yet… 1 Fathom is 6 feet, the height of a man, plus all seaman since time immemorial can stretch their arms to measure out an accurate fathom of line!

So if looking up at the stars and feeling incredibly small, you can relate the size of your body to our planet! Very empowering, I find!

However, whilst the Nautical Mile is based on meaningful stuff, the Kilometre, which was based on an incorrectly calculated minute of arc of Departure (the physical length of a minute of arc of Longitude) at the latitude of Paris. (Although it is now pretended that it was calculated from the distance between two church spires!)

Every aircraft also uses Nautical Miles for the reasons it is used at sea.

If unconvinced, try finding a KM scale on a chart, or chart plotter. You won’t and its non-viable, as these portray a curved surface on a flat screen, using the Mercator’s projection and distort and stretch the Longitude scale to effect this. However, the latitude scale is accurate and 1 minute of latitude equals 1 Nautical Mile. (There are some wrinkles to this but that is for another day).

This is not to say that the Metric system is rubbish – it certainly isn’t – but its use at sea is absurd and meaningless! The only other organization I am aware of that uses KM at Sea is the diabolical BBC who have been trying to force Metres and KM etc down our throats for years. And yes, I am from the UK!

Tags: , ,



Back to Top ↑

Get Your Sailing News Fix!

Your daily or weekly download by email.

Subscribe - In popup

  • This field is for validation purposes and should be left unchanged.

We’ll keep your information safe.