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Nautical Measurement

Introduction

The need for planning is one of the best experiences of traveling.  The fun of travel is that sometimes this planning entails packing, logistics, planes, choices, and much more.  However, when it comes to figuring out distances, nothing compares to the significance of trip planning.  Some will calculate the distance in kilometers, while others will use miles, and yet others will use weeks.  No matter how you gauge a journey, it is undeniable that travel is important in measuring the distance between locations.

What if you plan to travel on land and water?  What difference will it make?  This was discovered by early explorers, who created two different distance measurement systems: one for land and one for the open sea.

This article will explore nautical measurements and other important terms related to the distance traveled through the water.  We will also discuss the difference between nautical miles and knots.

What is nautical measurement?

Definition

Nautical measurements are units used for distance and speed movements in maritime and air navigation. 

The distance traveled through the water and air is measured in nautical miles.  A nautical mile is equivalent to 1.1508 land-measured (or statute) miles, which is a little more than a mile on land.  The nautical mile is calculated using the Earth’s longitude and latitude, with 1 nautical mile equaling one minute of latitude.

Nautical Measurement vs. Land Measurement

There is a significant difference between measuring distances on the ocean versus on land, despite the fact that we don’t usually think about it. Since there are no obstacles on the route at the open ocean, the Earth’s curvature must be added as a measuring variable. On land, there are many different kinds of terrain features, including mountains, valleys, hills, dips, and crevices. As a result, every measurement requires a separate unit. We use terminologies like nautical miles and terrestrial miles. As a result of our planet’s curvature, which is easily felt in open water and, of course, in the open air as well, they provide varied outcomes.

Nautical Chart

One of the essential tools a mariner can use is a nautical chart.  It is a map that shows how the seafloor and coastline are organized.  It offers information on the depths of the water, the positions of navigational hazards, the locations and features of navigational aids, anchorages, and other features.

To navigate safely, a nautical chart is necessary.  Navigators use charts to plan trips and guide ships safely and efficiently.

Nautical Mile vs. Knot

Nautical Miles

The distance traveled through the water is measured in nautical miles.  A nautical mile is equivalent to 1.1508 land-measured (or statute) miles, which is a little more than a mile on land.  The nautical mile is calculated using the Earth’s longitude and latitude, with 1 nautical mile equaling one minute of latitude.

Latitude and longitude coordinates are more helpful for long-distance travel since they allow for more accurate measurements considering the curvature of the Earth.  Latitude and longitude are used on nautical charts, making it much simpler for mariners to calculate the distance in nautical miles.  Latitude and longitude are also used for navigation in space travel and nautical miles to gauge distance.

Worldwide, the international nautical mile is in use.  It was formally determined in 1929 by the organization that is now known as the International Hydrographic Organization to be 1.852 kilometers.

How does the nautical mile work?

The equator is regarded as a circle.  That circle can be divided into 360 degrees, with each degree being divided into 60 minutes.  A nautical mile, also known as a statute mile, is a little longer than a standard mile.  One minute of a degree is equal to one nautical mile.  In actuality, a nautical mile is 1.1508 statute miles long, or 6,076 feet.  Hence, 1 nautical mile is around 1.15 miles.

The minute of latitude, not the minute of longitude, must be used as the unit of measurement for a nautical mile according to geometry.  This is due to the fact that latitude lines do not converge toward the poles as longitude lines do as they move away from the equator.

Mile vs. Nautical Mile

The nautical mile, based on the circumference of the Earth and corresponds to one minute of latitude, is a unit of measurement.

Based on land measurements, miles are often shorter than circumferences.  Earth is not perfectly spherical and tends to flatten towards the poles, which causes the difference.

We utilize factor 1.15 to convert the statute to a nautical mile.

Knots

Knots are used to calculate speed.  One nautical mile per hour (about 1.15 statute miles per hour) equals one knot.

The name “knot” first appeared in the 17th century, when sailors used a tool called a “common log,” which was a rope with regular knots fastened to a piece of wood formed like a slice of pie to gauge the pace of their ship.  The sailors lowered the wood piece into the sea and let it drift freely behind the ship for a specified amount of time (usually measured with an hourglass).  After the allotted time had passed, they would calculate their speed by counting the knots between the ship and the piece of wood.

Knot vs. Miles Per Hour

Both knots and miles per hour are units of speed.  The rate of an object’s movement or action is its speed. 

A knot is another speed measurement unit, similar to mph or kph but measuring one nautical mile instead.  Most often, the speed of boats and airplanes is expressed in knots.  On Earth, one nautical mile equals one minute of arc.  All countries utilize this standard unit of measurement for speed while traveling by air or sea. 

Exactly 1.852 kilometers, or 1,852 meters, make up one nautical mile.  One nautical mile is equivalent to 1.1508 statute miles in the English system of measurements.  The main applications of nautical miles are in navigation and charting.  Thus, a knot is essentially equal to one nautical mile per hour, or 1.1508 miles per hour.  This accurately translates to 1/60th of a degree of an arc of one minute.

Let us say, for example, a ship is traveling at a speed of 18 knots; we can say that it is traveling 20.7144 miles per hour or 33.329 kilometers per hour. 

Since 1 knot = 1.1508 miles per hour and 1 mile = 1.609 kilometers, we have the solution,

18 × 1.1508 = 20.7144 mph
20.7144 × 1.609 = 33.329 kph

Another example is, let us say, for 22 knots.

22 × 1.1508 = 25.3176 mph
20.7144 × 1.609 = 40.736 kph

The table below shows a typical comparison between knots and miles per hour.

KnotMiles Per Hour
The knot is a speed measurement unit that is non-SI.A typical unit for measuring speed is the mile per hour.
1 nautical mile per hour = 1 knot.Miles per hour is mph when abbreviated.
A knot is a minute of arc on the planet.Miles per hour is a scalar quantity.
A knot is utilized for navigation in the air and on the water.For general purposes of calculating speed, mph is utilized.
1 knot = 1.15 miles per hour 1 knot = 1.852 kilometers per hour1 nautical mile = 1.1508 statute miles

Speed Conversions

The table below shows the conversions of knots to mph and kph.

Speed Conversions

KnotsMiles per Hour
1 knot = 1.1508 miles per hour
Kilometers per Hour
1 mile = 1.609 kilometers
1 knot1.1508 mph1.8516 kph
2 knots2.3016 mph 3.7033 kph
3 knots3.4524 mph5.5549 kph
4 knots4.6032 mph7.4065 kph
5 knots5.754 mph9.2582 kph
6 knots6.9048 mph11.1098 kph
7 knots 8.0556 mph12.9615 kph
8 knots9.2064 mph14.8131 kph
9 knots10.3572 mph16.6647 kph
10 knots11.508 mph18.5164 kph 
11 knots12.6588 mph20.3680 kph
12 knots13.8096 mph22.2196 kph
13 knots14.9604 mph24.0713 kph
14 knots16.1112 mph25.9229 kph
15 knots17.262 mph27.7746 kph
16 knots18.4128 mph29.6262 kph
17 knots19.5636 mph31.4778 kph
18 knots20.7144 mph33.3295 kph
19 knots21.8652 mph35.1811 kph
20 knots23.016 mph37.0327 kph

The table below shows the conversions of knots to feet per hour.

KnotsFeet per HourKnotsFeet per Hour
1 knot6076 ft/h11 knots66836 ft/h
2 knots12152 ft/h12 knots72912 ft/h
3 knots18228 ft/h13 knots78988 ft/h
4 knots24304 ft/h14 knots85064 ft/h
5 knots30380 ft/h15 knots91140 ft/h
6 knots36456 ft/h16 knots97216 ft/h
7 knots 42532 ft/h17 knots103292 ft/h
8 knots48608 ft/h18 knots109368 ft/h
9 knots54684 ft/h19 knots115444 ft/h
10 knots60760 ft/h20 knots121520 ft/h

Examples

Example 1

Convert each given knot into miles per hour ( mph ) and kilometers per hour ( kph ).

( a ) 3 knots
( b ) 10 knots
( c ) 12 knots
( d ) 15 knots 
( e ) 25 knots

Solution:

Since 1 knot = 1.1508 miles per hour and 1 mile = 1.609 kilometers, we have the following solution:

( a ) 3 knots

3 × 1.1508 = 3.4524 mph
3.4524 × 1.609 = 5.5549 kph

( b ) 10 knots

10 × 1.1508 = 11.508 mph
11.508 × 1.609 = 18.516 kph

( c ) 12 knots

12 × 1.1508 = 13.8096 mph
13.8096 × 1.609 = 22.2196 kph

( d ) 15 knots

15 × 1.1508 = 17.262 mph
17.262 × 1.609 = 27.7746 kph

( e ) 25 knots

25 × 1.1508 = 28.77 mph
28.77 × 1.609 = 46.2909 kph

Example 2

If a boat is traveling at 18 knots, find its conversion to feet per hour.

Solution

Long distances over land are often measured in statute miles.  A nautical mile is typically used to calculate distances across the open sea.  A statute mile equals 5,280 feet, whereas a nautical mile is 6,076 feet.

1 statute mile = 5280 ft
1 nautical mile = 6076 ft

To convert 18 knots to feet per hour, we must multiply 18  knots by 6076 ft.  Hence, we have,

18 × 6076 = 109 368 feet per hour

Therefore, 18 knots is equivalent to 109 368 feet per hour.

Example 3

If a boat is traveling at 121520 feet per hour, find its conversion to miles per hour and knots.

Solution

Since the given is feet per hour, to calculate its conversion to miles per hour, we must divide the given measure by 5280.  Remember that,

1 statute mile = 5280 ft
1 nautical mile = 6076 ft

Hence, we have, 

121520 ÷ 5280 = 23.015 miles per hour

Since 1 knot = 1.1508 miles per hour, we must divide 23.015 by 1.1508.  So, we have,

23.015 ÷ 1.1508 = 20 knots

Therefore, 121 520 feet per hour equals 23.015 miles per hour or 20 knots.

Example 4

Which boat travels faster?  Boat A: 18 knots or Boat B: 20 miles per hour.

Solution

Let us convert 18 knots to miles per hour by multiplying 1.1508 since 1 knot = 1.1508 miles per hour.  Hence, we have,

18 × 1.1508 = 20.7144 mph

Boat B travels 20 miles per hour; Boat A travels a little more than 20 miles per hour.  So, Boat A travels faster than Boat B. 

Summary

In both air and sea navigation, nautical measures are the units of distance and speed movements.

The distance covered by air and water is expressed in nautical miles.  A nautical mile is 1.1508 statute miles or slightly more than one mile on land.  The nautical mile is based on the longitude and latitude of the Earth, with one nautical mile equaling one minute of latitude.

Nautical Chart

A nautical chart is an important tool a mariner can have.  It is a map that depicts the arrangement of the seafloor and coastline.  It provides details on the water’s depths, the locations of navigational dangers, the features of anchorages, and other factors, as well as the locations and characteristics of nautical aids.  A nautical chart is required to travel safely.  Navigators utilize charts to plan journeys and steer ships safely and effectively.

Nautical Mile

The distance traveled through the water is measured in nautical miles.  A nautical mile is equivalent to 1.1508 land-measured (or statute) miles, which is a little more than a mile on land.  The nautical mile is calculated using the Earth’s longitude and latitude, with 1 nautical mile equaling one minute of latitude.

Knot

A knot is another speed measurement unit, similar to mph or kph but measuring one nautical mile instead.  Most often, the speed of boats and airplanes is expressed in knots.  On Earth, one nautical mile equals one minute of arc.  All countries utilize this standard unit of measurement for speed while traveling by air or sea. 

Frequently Asked Questions on Nautical Measurement ( FAQs )

Why is the measurement system used for marine navigation different?

When traveling over vast distances, where the curvature of the Earth affects measurement accuracy, it is more practical to use latitude and longitude coordinates.  Mariners find it much simpler to determine the distance in nautical miles because nautical charts utilize latitude and longitude.  Latitude and longitude are also used in air and space travel and nautical miles to determine distance.

What is 1 nautical mile in kilometers?

Worldwide, the international nautical mile is in use.  It was formally determined in 1929 by the organization that is now known as the International Hydrographic Organization to be 1.852 kilometers.  Following that, the United States and the United Kingdom both utilized slightly different measurements; however, in 1954, the United States accepted the international nautical mile, while the U.K. in 1970.

Why do mariners use nautical charts?

A nautical chart is an important tool a mariner can have.  It is a map that displays the arrangement of the seafloor and coastline.  It provides details on the water’s depths, the locations of navigational dangers, the features of anchorages, and other factors, as well as the locations and characteristics of nautical aids.

A nautical chart is required to travel safely.  Navigators utilize charts to make plans for journeys and steer ships safely and effectively.

What distinguishes a nautical mile from a knot?

A nautical mile is a distance measurement, not speed.  The speed is measured in knots on the water, where one knot is equal to 1.15 miles per hour or one nautical mile per hour.  Seafarers can precisely express distance and speed on water due to the nautical mile and knot, which work together.

Why do we have different measurements for travels on land and water?

Despite the fact that we rarely consider it, there is a substantial difference in measuring distances on the ocean versus on land.  In the open sea, there are no obstructions in the way; hence the curvature of the Earth must be added as a measurement factor.  Mountains, valleys, hills, dips, and crevices are just a few of the many distinct types of terrain features that may be found on land.  As a result, a different unit is needed for each measurement.  We use terms like terrestrial miles and nautical miles.  They produce various results due to the curvature of our planet, which is easily felt on the open sea and, of course, in the open air as well.

What is the difference between knot and miles per hour?

The only difference between miles per hour ( mph ) and a knot is that knot is a non-SI unit of speed that equals one nautical mile.  Both mph and knot are speed measurements based on the distance traveled in a given amount of time.  A nautical mile is one-sixtieth of a degree of latitude.  Most often, knots are utilized for air and maritime navigation.  It explains how longitude and latitude relate to distance.  The nautical mile, which is based on the length of an arc minute along the equator, has a higher significance in navigational calculations.  A nautical mile, based on the Earth’s circumference, is simply one minute of arc on the planet.

The table below shows a quick reference of their difference.

KnotMiles Per Hour
The knot is a speed measurement unit that is non-SI.A common unit for measuring speed is the mile per hour.
1 nautical mile per hour = 1 knot. Miles per hour is mph when abbreviated.
A knot is a minute of arc on the planet.Miles per hour is a scalar quantity.
For navigation in both the air and on the water, knots are utilized.For general purposes of calculating speed, mph is utilized.
1 knot = 1.15 miles per hour 1 knot = 1.852 kilometers per hour1 nautical mile = 1.1508 statute miles

How do we convert knot to mph and kph?

To convert knot to miles per hour and kilometers per hour, we would need this information:

1 knot = 1.1508 miles per hour
1 mile = 1.609 kilometers

Let us say, for example, a ship is traveling at a speed of 21 knots; we can say that it is traveling 24.1668 miles per hour or 38.8844 kilometers per hour. 

We have the solution,

21 × 1.1508 = 24.1668 mph
24.1668 × 1.609 = 38.8844 kph

How many knots do ships usually travel?

Most cruise ships can cruise at a speed of 24 to 26 mph or 21 to 23 knots.  The distance to the next port, the height of the waves, and fuel efficiency are only a few of the prominent factors that affect the ship’s speed at any given moment.

What is the difference between the nautical mile and the regular mile?

The nautical mile is the measurement of the distance between any two points, whether they be reached by air or over water.  The distance between two points calculated by traveling from one location to another along an imaginary straight line on the surface of the Earth is referred to as a statute or regular mile.

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