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 may produce a cocked hat where the lines do not meet. The vessel is not guaranteed to be inside it if errors share a bias. Near danger, use the nearest corner as a conservative working assumption, add margin, and seek an independent fix.
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.
- 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
Watch for this: 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.
Continue studying Chartwork
This public lesson is part of Revision Module 10. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.