why do boats still use knots?


From what I know the vast majority of nautical travel is measured in knots. It just feels a little ancient for this world of technology. Wether it’s a ship or amphibious craft the speed is always knots. We have pretty reliable GPS and satellite nav nowadays even to the point you can buy a GPS speedometer for less than $50 for your car. I completely understand the “if it ain’t broke don’t fix it” philosophy but surely it would make life just that little bit easier for sailors and captains to have their speed in MPH/KPH?

In: 579

It’s because on the water, a “mile” isn’t 5280 feet. A “mile” is really a “nautical mile” and that’s defined as about 6075 feet. 1 nautical mile is 1.15 miles.

“Knot” is just the term for “nautical miles per hour” just as a car uses MPH/KPH.

Because they have always done that so all speed rules, installed equipment, etc use a knot.

A knot is a nautical mile per hour and a nautical mile is 1/60 of the latitude of eath. Because of this knots is a very good speed for navigation on the open seas where you define location with coordinates in degrees minutes and second. One minute of latitude is one nautical mile.

So all existing information about how long a sea jury is are in nautical miles. There is very seldom any need to converter between nautical miles, miles, and kilometers on the sea.

If you measure the distance on earth on a globe and get how many degrees it is a multiplication of 60 gives you the distance in nautical miles. Divide it by the speed in knots and you get the travel time. Long-distance aviation as sea usually follows the shorted path on a globe, this is called the great circle distance.

You can do that measurement with a sting you stretch out on a globe and then then it is not hard to get its lengths in degrees.

A change to another unit would have no advantages at but disadvantages from the point of navigation.

For the same reason, a lot of flights use natural miles and knots for speed. It makes sense when you are not bound by the path of a road.

To secure the boat from floating away.

Jokes aside, knots mean nautical miles per hour and they are used to measure travel over the surface of a sphere (Earth) as an angle. Ships traveled far enough over water such that the curvature of the Earth factors into their speed and distance. A nautical mile is equal to 1 minute of latitude. 60 nautical miles is 1 degree of latitude.

Your GPS will give you coordinates like 32° 10′ N, 10° 0′ W.
How far is the coordinate 32° 11′ N, 10° 0′ W?
You can work out how far that is in KM.
But I can tell you right now that it’s ~1 nautical mile away.

That’s why Knots are a thing, it’s easier to work with coordinates.
Coordinates GPS still gives you.

Why would it make their life easier in MPH/KPH?

Knots is just a measure of speed in nautical miles per hours. So the real question here is why nautical miles. Well you see on land you can measure a distance, you put a tape on the ground and measure. But on water you can’t do that. But what you can do is have instrument that measure your latitude. 1 minute of latitude equal 1 nautical miles.

So yes ok now you can use GPS to calculate your speed in whatever you want, but what if the GPS doesn’t work? Now your gonna need to calculate your stuff using manual equipment and it’s gonna give you an amount of nautical miles. Yes ok for a multi million dollar ship, you might have back up, but most ship are small. Then you need to ask yourself, would it make sense to change everything from nautical miles to miles? All the textbook, all the instrument, all the charts and map. Everything?

And for what? What improvement to their life will all that effort and risk bring to sailors?