MARITIME – DEAD RECKONING & COATAL NAVIGATION CALCULATOR
Position Fix Running
A precise tool.
What is the Position Fix Running & How does it work?
A running fix is a classic dead‑reckoning technique used when a navigator can take two bearings on the same target at two known times while the own‑ship is moving. By combining the ship’s own motion (speed, course, and elapsed time) with the two observed bearings, the exact position of the target can be triangulated.
First the vessel’s new position after the elapsed interval is calculated using the dead‑reckoning (DR) formula. The travelled distance (d) is simply the product of speed (V) and time (t):
Next, two lines are drawn from the two ship positions, each at the observed bearing to the target. The intersection of these lines gives the target’s latitude and longitude. This method assumes a spherical Earth and uses great‑circle navigation equations for the most accurate result.
d = V times t
V = speed (knots), t = time (hours)
Parameters
Result
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Frequently Asked Questions
What is a running fix in navigation?
A running fix is a dead-reckoning technique where you take two bearings on the same target at different times while moving to determine its exact position.
How do I calculate the new position of my vessel using a running fix?
First, use the DR formula with speed, course, and elapsed time to find your new position. Then, triangulate the target’s position using the two bearings.
What information is needed for a running fix calculation?
You need your vessel’s speed, course, elapsed time, and two bearings on the same target taken at different times.
Can I use a running fix with only one bearing?
No, you need at least two bearings on the same target to accurately triangulate its position using a running fix.
What is the purpose of dead-reckoning in navigation?
Dead-reckoning helps estimate your current position by calculating your past course and speed from a known starting point.
How does a running fix differ from a single bearing fix?
A running fix uses two bearings taken at different times while moving, allowing for more accurate triangulation of the target’s position compared to a single bearing fix.
What is the importance of elapsed time in a running fix calculation?
Elapsed time is crucial as it determines how far your vessel has traveled since the first bearing was taken, affecting the accuracy of the triangulation.
Results are for informational purposes only and do not constitute professional advice.