Marine Navigation

The Art and Science of Finding Your Way


It is reasonable to assume that the first navigational activities began on land and it is also reasonable to assume that, when humans ventured out onto the water, the knowledge learned on land was applied at sea. Generally, that knowledge was based on our basic senses, the senses of seeing, smelling and hearing. The most significant of these would be seeing, which is exemplified by the term “Landmark”. Familiarity with your surroundings will always assist you in finding your way.

As humankind evolved and gained a better understanding of their surroundings, they ventured further and further away from their familiar “backyard”. The need to find one’s way becomes more important as the distance from home increases. The art and science of safely finding your way, would only become more sophisticated with time.


A Very Brief History of Marine Navigation


The first bits of navigational knowledge were gathered through observation and passed on by word of mouth.

When humans first ventured out on the water, it was very likely that his only available navigational tool was the sight of a familiar piece of land. Losing sight of that familiar “landmark”, meant immediate disorientation and the chances of returning safely were about 50-50, at best.

It was likely very early in human history, when we realized that the sun arrives on the horizon at more or less the same spot everyday and goes below the opposite horizon at more or less the same spot every day. It would be sometime later when, through persistent observation, we would identify the summer solstice, the fall equinox, the winter solstice and the spring equinox.

Following the discovery of loadstone (magnetite) thousands of years ago, someone observed that, for a given location, the magnet had a tendency to align itself on the same axis for that location. It is no coincidence that this alignment represented the rotational axis of the earth. This alignment would eventually be referred to as north and south. Before long, a navigator would develop the first rudimentary compass. Knowledge of your direction is the most fundamental piece of information used in navigation. The mariner now knows that sun rises in the East and sets in the West. He also has a compass that aligns North and South. A universal navigational vocabulary is being defined.

Another discovery came when a stargazer living in the northern hemisphere noticed that, there was a star that did not appear to be moving, while all other stars in the heavens were constantly in motion.  Familiarity with the night sky allowed the keen observer to identify the “pole star” or the “north star”. The “north star”, also known as Polaris, is more or less permanently sitting over the north pole and when visible provides the navigator with a directional reference. Not only does the “north star” indicate direction, but it’s elevation above the horizon would indicate whether or not your direction of travel has a north of south component.

Following these discoveries, one piece of information remained illusive until the eighteenth century. The compass enabled navigators to determine direction of travel, while the measured elevation of heavenly bodies above the horizon would indicate the north-south component of your travel. Determining the east-west component of your travel remained a challenge. Although the relationship between time and longitude was well understood, a accurate timepiece durable enough to withstand the rigors of long ocean voyages had yet to be developed.

By the middle of the eighteenth century, John Harrison’s pocket watch proves to be both accurate and durable enough to determine longitude at sea.

Global positioning was now achievable on long ocean voyages. The ability to determine the ship’s position provided navigators with an accurate navigational system that worked on the worlds largest oceans. Safety at sea had improved significantly.




Conning is one those English words that has more than one meaning. The word is most often used to describe a process of deception by persuasion.

Although somewhat less familiar, the word conning is also used to describe the steering of a ship or vessel. More precisely, it describes the steering of vessel using visual aids, e.g. “landmarks” . Man’s ability to con his way, whether on land or on the water, depended for the most part on his knowledge of the area. Conning is used in confined waters, e.g. harbours, restricted channels.

If you are unfamiliar with the area, your ability to con or navigate is limited to avoiding collision with the most obvious like the coastline, islands and rocks awash.

An important component of conning is a knowledge of the area (sometimes called “local knowledge”). This knowledge of the area would include a knowledge of what is not visually obvious, like rocks and shoals, depths and currents. In the early days of navigation, this knowledge was gained empirically and passed on by word of mouth.

Although conning, as a navigational tool is not new, the method remains an important part of navigating in confined areas, like harbours, rivers, narrow channels and near shore.



When we think of piloting, we have a tendency to think of airplanes. In the nautical world, piloting is the process of steering a boat safely in confined waters, such as harbours and narrow channels, using all available information such as landmarks, aids to navigation, soundings, tidal information, speed, dead reckoning information, Radar and GPS.

Piloting by profiles refers to process by which a mariner cons his/her way safely through dangerous waters. By using landmarks as “leading marks”, the skipper can avoid known underwater dangers. This is done by identifying ranges. A range refers to the alignment of two or more natural features, such as hills. Based on a knowledge of the area, you can sometimes avoid underwater dangers, like a reef, by aligning your course with the alignment of two or more natural features.

Most ports in Canada employ harbour pilots. These pilots are experienced and qualified ship’s captains, with a sound knowledge of the port for which they are employed. When foreign vessels arrive at these ports, the harbour pilot is ferried to the vessel, at which point, the harbour pilot is responsible for piloting the vessel into the harbour. Upon departure, the harbour pilot will again pilot the vessel out of the harbour.

Good conning skills and the careful application of all available information should result in good piloting skills and the safe navigation of dangerous waters.


Latitude and Longitude


In two-dimensional space (assuming the surface of the earth to be two-dimensional), two coordinates are required to define or describe a position. In other words, a grid system. The grid system used on planet earth is referred to as Latitude and Longitude. If you know your Latitude and Longitude, then you know where you are on the surface of the earth.

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Nautical Charts


The first nautical chart may have been a drawing of a coastline, drawn by and passed on by, a mariner with a knowledge of the coastline, to a mariner with no knowledge of the coastline. This graphical representation of the area may have been quite simple, but nonetheless a very useful aid in navigating the area.

Over time, the nautical chart would evolve into a sophisticated document containing a wealth of information about a given body of water. Today’s nautical charts show the directions, the distances, the dangers, the safe routes, the depths, and much, much more. They also provide a means to determine positions, using a grid system of Latitude and Longitude.

Besides being a source of information, nautical charts are drawn to scale and can be used to determine distances and directions. By using the information provided by your compass and a knowledge of your boat’s speed through the water, an estimated or “dead reckoning” position can be plotted on a chart. The ability to plot “dead reckoning” positions on a nautical chart becomes a most useful navigational tool on long passages over open water. It becomes even more important when the navigator is out of sight of land.

Dead Reckoning


Most boats today have electronic instruments that indicate the boat’s “speed through the water”. The most basic instruments are connected to a transducer that is coupled to a small paddle wheel installed in the hull of the boat. As the boat moves through the water, the paddle wheel turns and the speed is transmitted electronically to a digital readout at the helm.

One of the outputs of today’s GPS is boat speed. The boat speed calculated by the GPS is different from an onboard instrument reading, in that it calculates the speed over the surface of the earth or the “speed over ground”. The difference between the “speed through the water” and the “speed over ground” is explained by the effects of the wind on a vessel and/or the movement of the water relative to the earth, i.e. water currents.

Although the surface of a sphere (the earth) cannot be accurately portrayed on a flat piece of paper, a relatively small area (a few hundred nautical miles) can be portrayed with negligible distortion.

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Coastal Navigation

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Offshore Navigation

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Celestial Navigation

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Electronic Navigation


From the first echo sounders in the 1920s to the satellite based Global Positioning Systems of the 1990’s, electronics would have a profound effect on marine navigation. The list of developments of the twentieth century is long and include VHF (Very High Frequency) radio, depth sounders (Sonar), radar, shoran, loran, GPS (Global Positioning Systems), electronic charts, chart plotters, as well as instruments that are capable of integrating all of these components and producing visual displays and overlays. Electronic Global Positioning Systems became the most important advancement in marine navigation since the development of the magnetic compass. There is no doubt, that finding our way has become a lot easier.


The more recent developments…..



Not long ago the VHF radio was a basic 2 way radio used for voice communication. Digital Selective Calling (DSC)As of 1999, the Safety of Life at Sea Convention (SOLAS) requires all passenger vessels and most commercial vessels to equip their vessels with Digital Selective Calling (DSC).


What is DSC?


Most importantly, Digital Selective Calling (DSC) allows mariners to instantly send a automatically formatted message to rescue authorities and other vessels. Communications on the hailing Channel under certain circumstances can be heavy.

Before you can effectively use your DSC equipped VHF radio, you will need to input your MMSI (Maritime Mobile Service Identity) number, which you get free of charge from Industry Canada. You will also need to connect a GPS to VHF radio. When getting your MMSI number, you will be required to provide some basic information about your boat, which will be placed in an electronic file under the MMSI number.

To make a distress call, you will need to hold the distress button on your radio for 5 seconds. A message will be sent to the coast guard, which will include your GPS position and activate your electronic file, which includes the information you provided about your boat.

DSC also gives you the ability to call other boats directly, providing that you have their MMSI number. If you have friends/boats that you call regularly, you will be able to call them directly. Your DSC equipped VHF radio very likely has a MMSI directory where you can enter MMSI numbers. Select the number tou would like to call and press call.


AIS (Automatic Identification System)


The AIS (Automatic Identification System) is similar to Digital Selective Calling (DSC) except that it continuously transmits/receives basic information about your vessel. Like DSC, AIS requires an antenna and a connection to GPS. The broadcast information includes MMSI number,  type of vessel, SOG (Speed over Ground), COG (Course Over Ground) and your position. This information can be shared with and displayed on chartplotter and RADAR displays. Most chartplotters/RADARS can apply an algorithm to this information to calculate and display the CPA (Closest Point of Approach) and TCPA (Time to Closest Point of Approach). AIS has contributed significantly to safely navigating in high traffic areas, particularly in low visibility conditions.


Navigation on the Web:


For  everything you ever wanted to know about navigation, The American Practical Navigator can be downloaded at: National Geospatial-Intelligence Agency.


“The art and science of finding your way by the sun, moon, stars, and planets and, in one form of another, is one of the oldest practices in human history.” for more, visit: Celestial Navigation.


If you have a need for Celestial Navigation Data visit: The U.S. Naval Oceanography Portal.


Want to be a safe boater, take a boating course. For more information, visit: The Canadian Power and Sail Squadron.




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