You're enjoying a beautiful day at sea when your Captain comes over the public address system to inform the passengers that your cruise ship is sailing at 20 knots. What does that mean?
Maritime navigational terminology isn't common knowledge for most. However, that doesn't mean you can't be curious about how fast your cruise ship is sailing!
While it might seem as though it's easier for miles or kilometers to be used, nautical miles and knots are the standard units of measurement for maritime navigation for a few reasons.
First, there are no landmarks in the middle of the ocean like on land, so Captains and sailors must rely on longitude and latitude at sea.
The system was designed to work with the Earth's geometry in open waters, and because the Earth is round, using miles or kilometers would be less practical. As such, nautical miles and knots are simpler units of measurement for navigation at sea.
What is a "knot"?
The formal definition of a knot is a form of measurement that equals one nautical mile. This is used to measure the speed of your cruise ship. Of course, this isn’t very helpful unless you also understand what a nautical mile is!
A nautical mile refers to the distance traveled by your cruise ship, which is a bit longer than a land-based mile. This is measured between two points of latitude on the globe. This type of measurement is used because of the Earth’s curvature.
Essentially, knots are used to measure speed, and nautical miles measure distance. One knot is equal to one nautical mile per hour. With a little conversion, one knot is equal to 1.15 land-based miles per hour.
For reference, most cruise ships travel around 20 knots per hour or roughly 23 land-based miles per hour.
However, the above is just an average. The mega-ship Oasis of the Seas has a high speed of 24.5 knots, or 28.2 miles, per hour.
If you're curious about your current speed when onboard, most cruise lines have a channel on their stateroom television that provides this information. It's quite interesting to compare speeds during the day to speeds at night!
Why is the speed measurement in water called a knot?
Back in the 17th century, sailors coined the term "knot" as a measurement of their speed using a device called a “common log.” This was a handy device used on the ship that consisted of a log with a rope and knots at regular intervals. The knots were attached to a piece of wood shaped like a triangle.
History states that sailors would lower the common log, covered in rope with knots, into the sea. The common log would float freely along the vessel for a specific amount of time.
Oftentimes, a sailor onboard the ship would watch the time by using an hourglass. Once the time was finished, the sailors would count the knots between the ship and the piece of wood, and this was used as their speed calculation.
International standard
The common log method might not have been precisely accurate, but it was close enough to give sailors the information they needed for navigation. It was especially innovative for navigation technology in the 17th century before the invention of advanced tools and gadgets!
While different countries use miles or kilometers, there is not a nautical kilometer measurement. The nautical mile is an international standard measurement used around the globe for maritime navigation. However, there was not always international agreement on what to classify as a knot because some countries used miles while others used kilometers.
The nautical mile was officially established in 1929 by the International Hydrographic Organization using nautical miles. Even so, the United Kingdom and the United States had used slightly different measurements. The U.S. officially adopted the international nautical mile in 1954 and the U.K. in 1970.
Allie Hubers
Allie Hubers has been cruising since she was a tiny toddler. What started as a yearly vacation with family quickly turned into a passion for travel, cruising and adventure. Allie's been on over 45 cruises all over the world. She even studied abroad on Semester at Sea, sailing the world on a ship while taking courses for college and visiting 4 continents.
