Chart No. 1 · J 2
M — Mud
Seabed
The italic letter M means a mud bottom — soft, usually reliable holding for anchors.
What it means
An italic 'M' on the water area marks a mud seabed. Qualifier prefixes refine it: 'soM' soft mud, 'sfM' stiff mud.
Why it matters
Mud gives excellent holding for most anchor types, though very soft mud may let a light anchor drag. Expect a dirty foredeck when you weigh.