Module 10 - Chartwork
Running Fix (Transferred Position Line)
A running fix allows you to fix your position using a single landmark observed at two different times. You take a bearing of the landmark, continue on your course, and then take a second bearing of the same object. The first position line is 'transferred' forward by the course and distance (including tidal stream) made good between the two observations.
Where the transferred position line crosses the new bearing gives your fix. This technique is essential when only one suitable object is visible — for example, a single lighthouse on an otherwise featureless coastline at night.
To transfer the position line accurately: advance every point on the original line by the course made good (water track + tidal stream) and the distance run between observations. Remember to account for tidal stream during the interval, not just course steered.
Key points
- Running fix = two bearings of the same object at different times
- Transfer the first position line forward by DR/EP movement
- Must include tidal stream in the transfer, not just course steered
- Useful when only one landmark is available
- Accuracy depends on quality of DR/EP between observations
Tip: A doubling-the-angle-on-the-bow technique is a special running fix: when the relative bearing doubles, the distance from the object equals the distance run between observations. This works well with a single light at night.
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