Charts, fixing and the EP
The Master works on Mercator charts, measuring distance on the latitude scale, and knows the projections, the datum, and the symbols of chart 5011. Position is fixed by more than one means — visual bearings and transits, radar ranges, the echo sounder, and GNSS cross-checked against them — and a running estimated position is kept from the course, the log and the tidal stream so any error is obvious. Parallel indexing is used to monitor the track past a danger, and the fix interval is matched to the waters.
- Fix by more than one means and cross-check; keep a running EP from course, log and tidal stream.
- Use parallel indexing to monitor the track relative to a danger or a mark.
- Match the fix interval to the waters — frequent in pilotage, less so in open water.
- Check the chart datum and apply any GNSS datum shift before plotting near danger.
WARNING — Cross-check near danger, always A confident but wrong GNSS position has grounded well-found ships. Near any danger, confirm the electronic position against a visual bearing, a radar range or the depth, and keep the running EP going.
TIP — Parallel indexing monitors the track A parallel index line on the radar lets the officer see at a glance whether the ship is holding her planned track past a danger, without a full fix — a powerful monitoring tool in pilotage and coastal waters.