1.6 Reading charts

Nautical charts use a bewildering array of symbols to convey information. The full list is found in a book ‘Symbols and Abbreviations Used on Admiralty Paper Charts’, also known as ‘Chart 5011’. However, sea kayakers only need to know a small proportion of these symbols.

Land on charts, above springs high water, is colored yellow. Deep sea appears as white, with blue used for shallow areas. Green is used to indicate parts of the seabed that can dry out at low tide, but which are covered at high water on a spring tide.

The numbers that cover a chart are depths. Underlined numbers are drying heights – i.e. how high that place will be above the water at a low tide. Both depths and drying heights are measured with respect to the ‘chart datum’ - generally the level of the lowest possible (astronomical) tide. The chart datum is the same as the zero used for tide tables.

Wiggly lines on charts, looking like waves, are used to indicate areas of rough water. Arrows are used to indicate tidal stream directions. Buoys are illustrated on charts using symbols that look like the shape of the buoy.

Chart of St. Mary’s Sound in the Scillies. Note the buoys on the chart - e.g. the lateral marks at the top (port mark called ‘Bacon Ledge’). In the sound we see two port markers at the NW end (around Bartholomew ledges), the more northerly of which is a buoy, the other being a post attached to the seabed. At the SE end of the sound is a north cardinal buoy (Spanish Ledge). Various features can be seen in Hugh Town including a church, a chimney and some slipways. There is a campsite on nearby Garrison Hill, although upmarket visitors stay in the Star Castle Hotel. A lighthouse is marked on Peninnis Head. The oval with a line across it in Saint Mary Pool marks the mooring for the lifeboat.

Chart of the tip of the Lleyn Peninsula. Note land (yellow) and areas that dry (green). At a very low tide, Maen Bugail (a rock just to the north of Bardsey Island) will be 4.1 m above the sea. Arrows indicate strong tidal streams in Bardsey Sound, with squiggles indicating potentially rough seas to the north of Braich y Pwll and over the Devil’s Ridge.