Obtaining Position Lines: Position lines can be determined using various methods such as celestial navigation, radar fixes, or electronic position fixes from GPS. These position lines represent the ship's location at a specific time.
Time Difference: To calculate a running fix, there needs to be a time difference between the position lines. The longer the time difference, the more accurate the running fix will be.
Plotting the Position Lines: Plot both position lines on the nautical chart, ensuring they are labeled with their respective times. It's important to accurately plot each position line with a fix symbol (e.g., a small circle or triangle).
Dead Reckoning (DR): Determine the vessel's course made good (CMG) and distance traveled during the time interval between the position lines. Use this information to plot a dead reckoning line (DR) from the most recent known position.
Transfer the Position Lines: Using a parallel ruler or a running fix plotter (a specialized tool), transfer both position lines perpendicular to the DR line. Make sure the position lines are transferred accurately and maintain their original angles to the DR line.
Intersection Point: The point where the transferred position lines intersect the DR line is the running fix. Mark this point on the chart with a fix symbol and label it with the corresponding time.
Assess Accuracy: Evaluate the accuracy of the running fix by considering factors such as the time interval between the position lines, the vessel's speed and course stability, and the accuracy of the original position lines.
Running fixes are particularly useful during longer periods between position fixes or when there is a need for more frequent and accurate updates on the ship's position. By utilizing running fixes in chartwork, seafarers can maintain a more accurate understanding of the vessel's current position and make necessary course adjustments to ensure safe and efficient navigation.
