COLREGs Rules 20–31
Lights & Shapes
Who is that at night? Every light configuration, rotatable in 3D with its arcs, day shapes, fog signal, and the patterns it gets confused with. Facts follow the USCG Navigation Rules; each entry cites its rule.
Power-driven
The Rule 23 baseline every other pattern modifies — masthead light, sidelights, sternlight.
Sailing
No white masthead light under sail — and what changes the moment the engine drives her.
Fishing & trawling
Rule 26: green-over-white for trawling, red-over-white for everything else fishing.
Hampered vessels (NUC · RAM · CBD)
Rules 27–28: vessels that cannot get out of your way — reds and red-white-reds.
Towing & pushing
Rule 24: stacked masthead lights, the yellow towing light, and what the tow itself shows.
Pilot vessels
Rule 29: white over red — pilot ahead.
Anchored & aground
Rule 30: riding lights, anchor balls, and the red-over-red of a ship on the bottom.
Other craft
Seaplanes and everything that borrows the power-driven pattern.
Now add the sound
In fog you hear a vessel before you see her — every configuration above links its restricted-visibility signal.
Light configurations and rule text follow the public-domain USCG Navigation Rules (International & Inland). All diagrams are original to boatrules.com.