Module 10 - Chartwork
Position Fixing
A fix is a position determined from observations — it is more reliable than a DR or EP. Common methods include: visual bearings (take compass bearings of two or three charted objects and plot them on the chart — the intersection is your fix), GPS/chart plotter position, and transits.
Three bearings produce a 'cocked hat' (small triangle where the lines don't quite meet). Your position is inside the triangle. If near danger, assume you are at the corner of the cocked hat nearest the danger.
At Coastal Skipper level you should also understand depth contour fixing (matching echo sounder readings to charted contours), radar range and bearing fixes, and the use of a single transit line combined with another position line for a fix.
Key points
- Fix = position from observations (more reliable than DR/EP)
- Three visual bearings give a 'cocked hat' fix
- Near danger: assume you're at the worst corner of the cocked hat
- GPS gives Lat/Long directly (plot it on the chart)
- Fix marked: ⊙ with time
- Depth contour + single bearing can also provide a fix
Tip: When taking visual bearings, take the bearing of the object changing most quickly first (usually the one nearest abeam), then the others. This minimises error from the boat's movement between observations.
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