Malone's Insights: What is a Knot?
- Apr 8, 2025
- 4 min read
Updated: May 22, 2025
Whether a cargo ship hauling millions of dollars worth of goods thousands of miles across the country to the small kayak you paddle only a few miles for your weekend fishing getaway, boats have become an ever-present mode of transportation in the 21st century.
But have you ever wondered: How do you measure how fast these vessels travel?
I hadn’t given this much thought until I came across a segment of Neil deGrasse Tyson’s podcast StarTalk, where he spoke on the topic. After watching the video, I wanted to know more.
After doing some more digging, I found the explanations online to be a bit lacking and confusing. Whilst writing notes on this topic for my one understanding, I decided to write an explanation that breaks the confusion.
Whether a boat is used for transportation or simple enjoyment, its speed is typically measured in knots. A knot is defined as one nautical mile per hour, which is approximately equal to 1.1508 miles per hour. Today, boat speed is measured using specialized electronic speedometers. The first patented boat speedometer I found was invented by Ted Kenyon and his company, Kenyon Instruments, in 1930. Interestingly, this was Kenyon’s first patent.
So, before 1930, did voyagers just guess how fast they were going?
Not quite. Long before the age of technology, sailors used a clever technique to estimate their vessel’s speed while traveling.
This method was called the Dutchman’s log, where a billet (typically a log) with a line or rope attached to it was thrown over the bow of the boat. As the ship moved forward, the length of the rope expelled during the emptying of a sandglass timer was the measure of the speed. The rope had knots spaced at equal intervals, allowing sailors to confidently estimate the speed of the vessel.
An English navigator, Richard Norwood, recommended using a line knotted in increments of 50 feet (15 meters) with a 30-second sandglass timer, or 47 to 48 feet (14.3 to 14.6 meters) with a 28-second timer.
By combining the distance (d) measured (via the knots) and the time (t) elapsed (via the sandglass), sailors could estimate their boat’s velocity (v).
Mathematical definition of velocity
Let’s explore an example:
While on a ship, the captain asks you to determine the boat’s speed so he can estimate how far it has traveled since 3:00 p.m. You grab the billet and its attached knotted rope, toss it over the bow, and simultaneously flip over the sandglass timer. Once the 30 seconds are up, you stop the rope and begin reeling it back in, counting 6 knots as you do.
You would report back to the captain that the boat is traveling at 6 knots. You may hear some erroneously say “6 knots per hour.” Considering the definition of the unit knots already takes into account time, hence “nautical miles per hour” therefore adding another unit of time (as I did above) would be “ 6 nautical miles per hour per hour” which is not velocity/speed but rather acceleration and would be incorrect.
[Bonus Question]:
If the boat maintained a constant speed of 6 knots from 3:00 pm to 7:00 pm, how far has it traveled?
Leave your answers in the comments!
To see a video of someone using the knot technique, follow the link below:
Today, boat speed is determined with much more precision, often using latitude and longitude coordinates.
However, while researching, some slightly different definitions arose that initially caused confusion.
One source defined a knot as an arcminute per hour. An arcminute is 1/60th of a degree, and if you follow the meridian of Earth, 1/60th of a degree equals roughly 1.1508 miles, consistent with the previous definition.
Another site defined a knot as a minute of latitude per hour. A minute of latitude is also 1/60th of a degree, again, aligning with the arcminute definition.
Although different wording was used, both definitions essentially describe the same concept. The confusion arises because each source leaves out part of the explanation that would tie everything together. The term that I believe both sites should have used is “arc minute of latitude.” This term encompasses both provided definitions and closes the gap of confusion.
To further avoid ambiguity, I suggest using the widely accepted and accurate definition:
1 knot = 1 nautical mile per hour, with one nautical mile being approximately 1.1508 statute miles.
No matter if you're using a knotted rope or GPS navigation, knowing your vessel speed is essential. The next time you are on a boat, take a moment to appreciate that even if your vessels power fails, you know a timeless method to measure your speed.
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Often, I find myself hyperfixated on a particular topic. It could be something we discussed in class or something random I saw on a billboard. When that happens, I get immersed in reading as much as I can to understand it fully. To help with my comprehension, I’ll take notes on what I find out.
Malone’s Insights is where I share those notes. So, if you're someone who enjoys learning about very random things, this series might just be for you. Hope you enjoy the ride!
Sources:
Featured Image - “Logs and Knots.” Hawaii.edu, 25 Apr. 2024, aerospace.windward.hawaii.edu/resources/curriculum/voyagers/logs-and-knots.html. Accessed 9 Apr. 2025.
“A Short History of Sailing Instruments Part 1 | B&G Sailing USA.” B&G Sailing USA, 2024, www.bandg.com/blog/racing/americas-cup/a-short-history-of-sailing-instruments-part-1/. Accessed 12 Apr. 2025.
“Dugout | Definition & Facts.” Encyclopedia Britannica, 20 July 1998, www.britannica.com/technology/dugout-boat. Accessed 12 Apr. 2025.
“Kenyon Gyro History.” KENYON GYRO, 2024, www.ken-lab.com/kenyon-gyro-history.html. Accessed 30 Apr. 2025.
Logsdon, Tom S, and S.S.D Jones. “Navigation | Definition, History, Measurements, & Facts.” Encyclopedia Britannica, 20 July 1998, www.britannica.com/technology/navigation-technology#ref363550. Accessed 4 May 2025.
Great post! To answer your bonus question, I believe the correct answer would be 27.6192 miles.