Quick Answer
Use Dead Reckoning when GPS is unavailable or unreliable, such as in dense forests or urban canyons, and when speed and course data are known. Conversely, use GPS for accurate long-distance navigation and precise location tracking.
Understanding Dead Reckoning
Dead Reckoning (DR) is a navigation technique that estimates a vessel or traveler’s position based on the distance traveled and direction of movement. It’s an essential skill for survival, especially in situations where GPS is unavailable or unreliable. DR relies on the user’s ability to accurately measure speed and course, which can be achieved using instruments such as a compass, a speedometer, or even simple observations of natural landmarks. For example, in a boat, you can use the distance traveled since the last known position and the speed to calculate the new position.
Calculating Dead Reckoning
To calculate DR, you’ll need to know your speed in knots or miles per hour, and your course in degrees. You can use a chart or a calculator to convert these values into a new position. For example, if you travel 10 nautical miles at a speed of 5 knots, and your course is 270 degrees, your new position would be 10 nautical miles west of your previous position. You can also use a navigation tool such as a sextant to measure the angle between the sun and a reference point, allowing you to calculate your latitude.
Integrating Dead Reckoning with GPS
In modern navigation, DR is often used in conjunction with GPS. By combining DR with GPS data, you can quickly and accurately update your position and course. This is particularly useful in situations where GPS signals are weak or intermittent. By using DR to estimate your position and GPS to correct and refine that estimate, you can navigate with greater precision and accuracy.
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