Ships travel the globe every day… They carry cargo and people from one port to another which may be half way around the world. Most of the typical voyage of a vessel is done far from the sight of land as the ocean is vast with no signposts to indicate directions. The navigator is responsible for understanding where the ship is located and also obeying the “Rules of the Road” or international maritime laws. Marine navigation is the process of locating your precise position on the ocean and using that knowledge to travel safely to your destination. Although modern navigators use electronic equipment relying on GPS (U.S.), Galileo (E.U.) and GLONASS (Russia) that can pinpoint your precise position anywhere on the globe, ancient navigators used a variety of methods to sail thousands of miles out to sea and return safely.

The idea of marine navigation goes back centuries to the first time someone ventured any distance on the water from land. There are several types of marine navigation and they all realate to the points of reference that are available to the mariner at any given time.
With the exponential growth in technology over the past century, it is easy to forget the non-electronic forms of navigation but it is critical that anyone attemping a passge of any length be equiped with the basic navigation skills such as dead reconing and celestial navigation.

Types of Marine Navigation

Wayfinding: Long before GPS, Loran C, chronometers, gyrocompasses, and other instruments of navigation that we now take for granted, the people of Polynesia, Phonecia, China, and Scandinavia were great seafarers. They travelled thousands of miles out to sea, populated other areas, and established communication and trade routes. Using only primitive instruments and an oral tradition of how to find their destination, they set out to sea. They were attuned to the motion of the stars, winds, tides, seasons and the habits of the birds to help them find their way.

Coastal navigation can be used to find a vessel’s position when it is near the shoreline. This method of navigation requires only a compass. This compass may be as simple as a magnetic compass which always points to magnetic morth or it may be a gyrocompass which points to true north. Determining a position relies on finding the bearing (direction) to known points which are visible on the shore. Knowing the bearing to any two points allows the navigator to plot on the chart a position or fix by triangulation. From that point, the distance to any other object or a turning point cna be determined. By plotting a series of fixes, and recording the time, the speed of the vessel can also be determined. During periods of good visibility any prominent points of land or other marks can be used to find position. At night, the lights and buoys maintained by the U.S. and Canadian Coast Guard can be used to obtain position fixes. During foggy weather or when out of sight of land, the navigator relies on dead reckoning to project where the vessel is based on the knowledge of the speed and direction of the vessel. Dead reckoning is subject to increased error as time elapses.

Celestial navigation relies on the motion of the earth relative to the sun and other stars to determine a position. In the northern hemisphere, the star most commonly used by the celestial navigator is Polaris (the north star). Using Polaris as a refenrce point has three major advantages:

1. It is one of the brightest stars.
2. It is easily found as the star at the end of the handle of the Little Dipper.
3. It is located directly above the North pole.

Since the Earth rotates on it’s axis running between the North and South poles, the stars in the night sky appear to move slowly in a circular fashion. At the center of this wheel sits Polaris. Because of this unique position, the navigator only needs to find Polaris to find which direction is North. In addition, because the star is so far away from Earth, the angle from the horizon to Polaris is the same as the latitude. This angle is measured precisely using a sextant. Although Polaris is a great gift to navigators in teh northern hemisphere, there is no bright star directly over the South pole to aid navigators in the southern hemisphere. Instead, there is only a void at the center of the wheel of the night. Once the latitude is known, all that is then required is to find the longitude. Unfortunately, finding longitude is more difficult. It relies on noting the time at which the sun or other stars rise, set, or reach a known position in the sky. This requires precise timekeeping, using a chronometer, and the use of the sextant. Since the Earth and other heavenly bodies move in precise paths and orbits, knowing the time at which a star sets, for example and the latitude can give the longitude.

Marine Navigation Charts are used to assist in all types of navigation as they typically show all land masses, water depths, channels, lights, buoys and hazards such as reefs, rocks and sand bars as well as any prominent features visible from the water such as church steeples. Navigators refer to charts of the area in which they are sailing to plot their position, course and speed as they travel. As a ship is sailing, the navigator takes fixes by referring to the electronic instruments, bearings to points of land, or sightings of the stars. This allows the navigator to always be aware of the ship’s location. Nautical charts are made following surveys of coastal areas. Old surveys such as those done by Captain James Cook and his crew required handlines with lead weights to measure water depths. Modern survey vessels use electronic instruments to measure water depth using sound. This information must be precisely placed on the chart in order to allow mariners to travel safely. Although nautical charts are normally thought of as paper documents, some vessels use an electronic chart to show position. An electronic chart displays the information from a paper chart on a computer. It also communicates with the elevctronic navigation equipment to automatically update the ship’s position as is moves. This provides additional capabilities such as automatically warning the mariner when a hazard is too close. Whether in paper or electronic form, a chart is crucial for navigators.

Electronic Navigation: Modern vessels have access to a variety of electronic methods of position finding. These systems use electronic signals to measure the range and bearings from the ship to a set of known points. RADAR stands for Radio Direction and Ranging. A radar sends out an electronic pulse which is reflected off ships, land, and buildings. By sweeping the radar antenna in a circle, the reflections can be plotted to give a radar image representing the objects surrounding the ship. A navigator can use the radar to measure the range and bearing from the ship to points shown on the radar image. This information can be plotted on the nautical chart. Then, knowing the position on the chart allows the navigator to determine the latitude and longitude of the ship. Position finding using radar is similar to coastal navigation except that radar has the advantage of being able to be used at night and in fog.
The Loran C system sends electronic pulses from stations at known locations on the shore. The travel time of the signal from the stations to the ship is used by a Loran C receiver to automatically calculate latitude and longitude. This allows a navigator to plot the ship’s position precisely on the nautical chart. Unfortunately, this system is limited to operations in coastal areas. The most common these days is the Global Positioning System or GPS. This system is based on measuring distances from the ship to a set of satellites which have been placed in orbit by the United States. This system uses twenty-four satellites in orbits which ensure that at least four satellites are able to be seen from any point on the Earth at any time. Knowing the distance from a ship to four satellites allows the instrumentation to display the latitude, longitude and altitude of the GPS antenna to within 100 meters anywhere on the Earth. A similar system has been launched by the Russian government. This system is known as GLONASS.