If your GPS fails, loses signal, or shuts down, do you still know where you are? Many sailors depend heavily on electronic navigation. Dead reckoning is a method that allows you to estimate your position using basic observations and consistent record keeping. It works independently of satellites and electronics.
Dead reckoning estimates your current position by projecting forward from a previously known location using your course, speed, and elapsed time. It does not require external fixes, but it does require discipline.
Why Dead Reckoning Still Matters
Electronic navigation systems are reliable until they are not. Equipment fails. Power systems go down. Antennas and connections degrade over time. When electronic navigation is unavailable, dead reckoning provides a way to maintain situational awareness and continue navigating safely.
Dead reckoning also strengthens your understanding of how your vessel moves through the water. Instead of relying solely on a plotted position from a screen, you develop a continuous mental picture of where you are and how you got there.
What You Need
To practice dead reckoning, you need:
- A known starting position
- A compass
- A method to measure or estimate speed through the water
- A reliable time reference
- A chart and a logbook
Step by Step Dead Reckoning
1. Establish a Known Position
Begin with a verified position on the chart. This can come from a GPS fix, a visual fix using landmarks, or any other reliable method. Record the position and the time.
2. Steer and Record Your Course
Steer a steady compass course. Record the compass heading you are steering. If the course changes, note the new heading and the time of the change.
3. Determine Your Speed
Measure or estimate your speed through the water. This may come from a speed log or from a calibrated engine RPM. Record the speed in knots.
4. Track Time Accurately
Time is critical in dead reckoning. Record the time whenever you begin a leg, change course, or change speed.
5. Calculate Distance Traveled
Distance traveled is calculated using speed and time. Distance equals speed multiplied by time underway.
6. Plot Your DR Position
From your last known or estimated position, draw a line on the chart in the direction of your compass course. Measure the distance traveled along that line and mark the new point. This is your dead reckoning position.
7. Update Regularly
Update your dead reckoning position at least once per hour and anytime your course or speed changes. Each update builds a continuous track of your estimated movement.
8. Verify When Possible
Whenever you obtain a reliable position fix, such as a visual bearing, depth comparison, or GPS fix, plot it and restart your dead reckoning from that verified position.
Accuracy and Limitations
Dead reckoning is an estimate. It assumes the vessel moves exactly as steered at the recorded speed. In reality, current can set the vessel off course, and wind can cause leeway. These effects accumulate over time and increase positional error.
Regular updates and frequent verification reduce this error and keep the estimate useful.
The Real Skill
Dead reckoning is not mathematically complex. The real skill lies in consistency. Recording data accurately, updating positions on schedule, and maintaining the log even when conditions are uncomfortable is what makes the method effective.
This is why dead reckoning remains part of formal navigation training. It forces attention, awareness, and accountability.
Bottom Line
Dead reckoning is a practical navigation skill that any sailor can learn. Start from a known position, record your course, speed, and time, and plot your progress regularly. Verify your position whenever possible. Many sailing schools teach the foundations of coastal navigation and dead reckoning.
A well maintained logbook is the foundation of dead reckoning navigation. Consistent records of position, course, and speed help you understand where you are and how you got there, even when electronics are unavailable.
