Chart No. 1 · K 31
Foul ground
Dangers
A hash-like symbol marks bottom fouled by wreckage — safe to sail over, terrible to anchor in.
What it means
The '#' symbol (often with the legend 'Foul') marks foul ground: remains of a wreck or other debris, not dangerous to vessels passing over, but to be avoided when anchoring, trawling, or grounding.
Why it matters
Foul ground is the classic anchor-eater. There is enough water to sail across it — just never put gear on the bottom there.