Charts, Publications and Passage Planning
Core concepts
Know the chart catalogue and how to read it: title block, scale, datum (usually WGS84 on modern charts), source diagram, units (metres or fathoms), chart symbols for dangers, buoyage, and the meaning of the 'sounding datum' (usually LAT). Understand the Notices to Mariners correction system and that an uncorrected chart is a hazard. Learn the standard publications: Sailing Directions, List of Lights, Tide Tables, and local port rules. Passage planning follows the familiar four-stage model: appraisal (assess the passage, crew, weather, and hazards), planning (waypoints, courses, distances, contingency anchorages, abort points), execution, and monitoring.
Traps
Exam questions like to test scale: a large-scale chart (e.g. 1:25 000) shows more detail over a smaller area; a small-scale chart covers more area with less detail. Another trap is chart datum versus chart datum for soundings - depths are below LAT, so the actual depth available is charted depth plus height of tide. Also watch for the difference between a drying height (above chart datum, shown underlined or with a specific symbol) and a charted depth.
Worked example
A chart shows a drying height of 1.2 m and the tide height is 3.4 m. Actual depth over the shoal = 3.4 − 1.2 = 2.2 m. If your draft plus safety margin is 2.5 m, do not pass.
Rule of thumb
Always add 'height of tide' to charted depth, but subtract a drying height. Plan the passage so no leg depends on a single unverified fix.