Marine Navigation

Back in the day, mariners had to rely on celestial navigation and Dead Reckoning to chart a course.

Dead Reckoning involves calculating present position based on direction and speed relative to a previous position. Dead reckoning is only as accurate as the successive measurements, and is therefore prone to error.

Celestial navigation is based on observation of the positions of the Sun, Moon, planets, and certain navigational stars. By knowing at which point above the earth a celestial object is, and by measuring its height above the horizon, the navigator could determine his distance from that point. A sextant was used to measure the celestial body's angular height over the horizon. A nautical almanac and a chronometer (a very accurate watch) were used to compute the position of celestial bodies above the earth. The angular height and position could then be used to create a circular line of position. Navigators would measure the position of a number of stars in succession, and use the overlapping lines of position to fix their position.

Piece of cake, right?

Marine GPS

Fortunately, modern navigators have much more accurate navigational aids at their disposal. One of the most widely used modern navigational tools is the marine Global Positioning System, or marine GPS.

Marine GPS units utilize signals transmitted from satellites in medium Earth orbit. A GPS receiver in a marine GPS unit can use these signals to establish location, speed, and direction to an extremely high degree of accuracy. With a marine GPS system, you can know your position to within a few feet.

Chartplotters use GPS to provide highly accurate navigational information. A Chartplotter is a marine navigation device that integrates GPS data with an electronic navigation chart (ENC). The chartplotter displays the ENC along with the position, heading, and speed of the boat. Integrated navigation systems may also display additional information from radar, sonar, and other sensors.

A marine chartplotter shows (plots) the position of a ship or boat on a video display, relative to the electronic nautical chart displayed in the background. This enables you to see exactly where you are relative to marine hazards, landmarks, and all of the other navigational information on the chart.

Modern marine GPS and navigation systems can make boating safer and less stressful, and are inexpensive enough that even a casual boater can - and probably should - install one on their boat.

But you should not rely solely on a marine GPS unit. Modern electronic navigational devices are incredibly useful and generally reliable, but electronic components can still occasionally fail, especially in a harsh marine environment. You should still carry the applicable paper navigational charts on board, and obviously you should have a basic knowledge of marine navigation before setting sail.

Don't know where to start? Just do a Web search for €boating rules,€ €boating classes,€ €boating education,€ or €marine navigation classes,€ and tack on your location. The results should point you to several good resources on marine navigation.