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Reading Navigation Lights at Night
💡 A vessel's lights encode its type, which side faces you, and its heading — decode them before you apply any give-way rule.
After dark you can't see a hull, a flag, or which way the bow points — you see only lights. The COLREGS turn that to your advantage by giving every vessel a lit signature that reveals three things: its type, its aspect (which side is facing you), and its rough heading. Recall from earlier cards that you can't decide give-way versus stand-on until you've identified the other vessel — at night, its lights are that identification.
Start with the core set every power-driven vessel underway shows. Sidelights are coloured and narrow: red to port (left), green to starboard (right), each covering a 112.5° arc from dead ahead to just behind the beam. The sternlight is white, covering the 135° arc behind. A forward-facing white masthead light (225°) sits higher up. A simple mnemonic: red–port–left are all short words.
Now read the scene. Both red and green together (plus masthead) means the vessel is pointing at you — a head-on situation. Only one sidelight means you're seeing its side: a red light means its port side faces you, so it's crossing from your right to your left; a green light is the mirror. Only a white light means you're behind it — you are the overtaking vessel.
Extra lights reveal type. A sailing vessel shows sidelights and a sternlight but no masthead light — that missing forward white light is the key giveaway versus a power-driven vessel. Vertical pairs signal special status, remembered by rhymes: "red over red, the captain is dead" (not under command), "red over white, fishing at night" (a fishing vessel), "green over white, trawling at night."