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Learn the Sea
Chart symbols & abbreviations
learnthesea.com
A quick-reference of the symbols you meet most. The full set is in the Admiralty 5011 booklet; these are the ones worth knowing by heart.
Depths, heights & dangers
| Symbol | Meaning |
|---|---|
| Soundings | Charted depth below chart datum (the lowest the tide normally falls) |
| 2̲·1̲ (underlined) | Drying height — metres the feature dries ABOVE chart datum |
| Wk | Wreck |
| Obstn | Obstruction |
| Foul | Foul ground — don’t anchor or trawl |
| PA / PD | Position approximate / doubtful |
| ED / SD | Existence doubtful / sounding doubtful |
Tidal levels
| Symbol | Meaning |
|---|---|
| CD | Chart datum — the level depths are measured from |
| MHWS / MHWN | Mean high water springs / neaps |
| MLWS / MLWN | Mean low water springs / neaps |
| HAT / LAT | Highest / lowest astronomical tide |
Lights
| Symbol | Meaning |
|---|---|
| Fl | Flashing — light shorter than dark |
| Oc | Occulting — light longer than dark |
| Iso | Isophase — equal light and dark |
| LFl | Long flash (two seconds or more) |
| Q / VQ | Quick / very quick flashing |
| Fl(2)G.10s | Group flashing twice, green, every 10 seconds |