Which chartwork equipment is useful?
A Portland plotter or parallel rulers, dividers, a sharp pencil, an eraser and a suitable calculator are common choices. Your training centre should confirm the exact equipment and current training chart or almanac material required for its assessment.
Keep the pencil sharp and lines thin. Label positions, times, bearings and units clearly enough that another navigator can follow the working. Neatness is not decoration; it makes an incorrect assumption easier to find.
How should latitude and longitude be plotted?
Find latitude on a side scale and longitude on the top or bottom scale. Use dividers to transfer the required spacing from a nearby graduation, mark the position precisely and label it with the relevant time.
For practical Mercator chartwork, one minute on the nearby latitude scale represents one nautical mile. Measure distance on that latitude scale, not on the longitude scale: meridians converge on the Earth, so one minute of longitude is not a nautical-mile distance scale.
How is a course to steer constructed?
Course to steer is the direction through the water that should produce the intended ground track after allowing for tidal stream and, where relevant, leeway. Work in true directions first, then apply variation and deviation if a magnetic or compass course is required.
For a one-hour construction, draw the tidal stream vector from the start. From its end, use the vessel's through-water distance to intersect the intended ground track. The line from the end of the tidal vector to that intersection is the required water track.
What is the difference between DR and EP?
A dead-reckoning position is advanced from the last known position using course steered and distance logged. It does not include tidal stream or leeway. An estimated position adds those estimated effects.
An EP may be a better estimate, but it is still only as good as its inputs. Mark positions using the notation required by your course materials, label the time and carry an uncertainty allowance near danger.
How should a position fix be checked?
A fix is a position derived from observations, but every fix has uncertainty. Common methods include intersecting bearings, transits, a running fix and an appropriately checked GNSS position.
Choose clearly identifiable charted features with useful angular separation and take observations promptly. A cocked hat shows that plotted lines did not meet perfectly; it does not prove the vessel lies inside the triangle. Cross-check with depth, contour, another observation and a conservative position when danger is nearby.
Primary sources
Compass Revision is an independent revision aid and is not affiliated with or endorsed by the RYA. Check current official publications, charts, forecasts and local directions before making a real passage or safety decision.