Module 7 - Charts & Publications
Interpret Symbols, Soundings, Tints, and Drying Heights
ADMIRALTY NP5011 gives the symbols and abbreviations used on ADMIRALTY and International Chart Series paper charts; IHO INT 1 is the international chart-user key. These references cover hydrography, topography, hazards, aids and services. Symbols on an ENC or leisure plotter may be portrayed differently, so use the maintained symbol key or Chart 1 for that system rather than assuming the paper symbol is identical.
Colour supports interpretation but is not a complete rule. On familiar multicolour paper charts, tints help distinguish depth bands and drying areas, but the relevant contour values, legend and notes control the meaning. Electronic day, dusk and night palettes can alter appearance. Never decide that water is safe simply because it is white, blue or untinted.
A sounding is a charted depth referred to the chart's stated vertical datum and units. On a modern metric UK chart, 3.2 commonly means 3.2 metres below Chart Datum. A drying height is an elevation above Chart Datum, commonly shown as an underlined figure on paper charts. Actual or predicted water depth still depends on tide, weather, uncertainty and the vessel's clearance policy.
| Chart item | Meaning to establish | Decision check |
|---|---|---|
| Sounding | Depth below the stated Chart Datum in the stated units | Add the applicable height of tide, then allow for uncertainty and UKC |
| Drying height | Feature height above Chart Datum | Subtract it from height of tide to estimate water over the feature |
| Depth contour | Boundary of a charted depth band | Relate it to draught, tide, survey quality and route margin |
| Colour tint | Visual support for a band or feature | Confirm with legend, contours, notes and display palette |
| Symbol or abbreviation | Meaning defined by the relevant chart reference | Use NP5011/INT 1 for paper or the system's maintained ENC key |
Optional quick check
Section 2 of 5
A metric chart shows a 2.4 m sounding and the predicted height of tide is 1.8 m. What is the initial predicted depth?
Sources and factual review
Continue studying Charts & Publications
This public lesson is part of Revision Module 7. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.