Sailing has it’s own terminology, including knots, keels, fore and aft. Sooner or later, new sailors ask want to know how fast a knot is. The answer is not very fast. I know because I looked it up. Here is what I found:

**A moderate sailboat speed is 3-4 knots. A knot is about 1.15 mph (1.85km/h). Three knots is equivalent to 3.4523383441 mpg (5.556 mk/h), or about the same speed as an adult walking quickly, so not very fast. Faster speeds are possible. **

In this article I will cover knots and comparisons to other measurements. Then I will cover some other questions. How this measurement came about is rather interesting.

## What is a Nautical Knot?

**A “knot” is a measure of speed and is defined as one nautical mile per hour. A nautical mile is defined by multiplying the number of degrees in a circle, 360 degrees, times 60 minutes, to arrive at 21,600 units, which (at the equator) are 6080 feet in length.**

## What is a Nautical Mile?

**A Nautical Mile is defined as exactly 1852 metres (6076 ft; 1.151 mi). It used to be defined as one minute (1/60 of a degree) of latitude. A Nautical Mile is also used in air, marine, and space navigation, and for the definition of territorial waters.**

The earth year is made up of approximately 365 days. The similarity to a circle with 360 degrees is not likely a coincidence. However, the exact details are apparently lost to recorded history, at least for now.

### 360 Degree Circle

The concept of a circle having 360 degrees dates at least from the Sumerians who created a calendar with 360 days in the year. The Sumerians used a base-60 numbering system. They divided each degree into 60 units. This is that we still use today as minutes of arc.

The Gregorian calendar is a circle of 360 divided by 12 months. The zodiac is also a circle of 360 degrees, divided by 12 signs. Most other (Jewish, Muslim, Bahá’í) calendars are based on a 360 degree circle, with adjustments for the extra days in the year.

Some time after that, the Greek scholar Eratosthenes (276 BC – 195 BC) accurately determined the circumference of the earth.

### 60 Degrees

If you multiply 360 by 60 you will arrive at 21,600 units. This number is a convenient measure of the earth’s circumference. This makes for easy math with no fractions or rounding errors. This is also very useful for a number of reasons, not just convenience. Early navigation was difficult enough without fractions.

### One Nautical Mile

One 60th of a degree, or one minute of arc, equals one nautical mile. This is equivalent (at the equator) to being 6080 feet. This is where the expression “a minute’s a mile” comes from.

Some have said the definition of a nautical mile is 6080 feet. While this is true, it’s not accurate. This a result of the calculation, not the cause of it. All of this was 2200 years before GPS and “Where in the world is Marco Polo.”

## How Fast Can You Sail a Sailboat?

Most sailboats cruise at a speed of 4-6 knots or 4.5-7 mph (6.4-11.26 km/h), with a top speed of 7 knots or 8 mph (13 km/h). Larger racing yachts can easily reach speeds up to 15 knots or 17 mph (28 km/h), with an average cruising speed between 6-8 knots or 7-9 mph (11.26-14.48). Cruising speeds of over 8 knots are not common.

These speeds are not consistent. Wind speeds change intensity and direction frequently. Predicting how long it will take to get to a destination is highly dependent upon multiple factors beyond your control.

## How Many Nautical Miles Can You Sail in a Day?

In ideal conditions, a typical cruising yacht can manage between 150–200 nautical miles in 24 hours. Powered boats can achieve 500 Nautical Miles in a day. A multi-hull racing yacht set the 24-hour world record in 2009 at 908 nautical miles.

"The top speed is usually a function of the "hull speed"

### Sailboats (4-6 knots)

Assuming you have consistent wind, a cruising sailboat’s speed is limited by the “hull speed”. The hull speed is a calculation equal to 1.34 times the square root of the waterline length.

To better understand this, let’s take an example. My 40′ sailboat has a waterline length of 32.5′ yielding a hull speed of 7.6 knots or about 180 nautical miles per day. Obviously winds and/or currents will contribute to the actual results. Further, not everyone sails at night.

### Catamarans (9-10 knots)

The narrow-hulled catamarans and racing catamarans can have a slightly larger factor. Maximum hull speed is approximately 1.3 times the square root of the waterline length. Some yachts can spend some of the time semi-planing. As a result, their hull speed is faster.

## Conclusions

In conclusion, the knot makes perfect sense. Being a land based person for much of my life, I had often wondered about knots and Nautical Miles, and how they came to be. Now I know.

Nautical charts, even the digital ones, have a grid of lines that mark the longitude and latitude lines. A Nautical Mile has a direct relationship to these lines. A knot is the measure of speed based on the Nautical Mile.

**Sources:**

https://www.britannica.com/science/mile

https://en.wikipedia.org/wiki/Mile

https://en.wikipedia.org/wiki/Nautical_mile

https://www.unitconverters.net/speed/knot-to-mph.htm

https://www.checkyourmath.com/convert/speed/per_hour/mph_km_per_hour.php

https://oceanservice.noaa.gov/education/tutorial_currents/06measure2.html