What a ship signal can tell you. And what it cannot.

A short introduction to received vessel signals and their limits.

The Automatic Identification System, usually called AIS, broadcasts messages from equipped vessels. Depending on the message, a receiver may learn a vessel’s position, speed, course or identifying details. AIS data is one ingredient in many vessel maps.

A vessel on a map is a received report, not a promise that its position is current. Reception, transmission intervals and the route between receiver and app all influence freshness. Some vessels may be missing from a particular feed entirely.

A responsible viewing experience makes the report time visible and distinguishes missing data from an empty harbor. Smooth animation can make a screen attractive, but it should never disguise an old report as a fresh observation.

Wakewing labels the vessel connection state on the map. An active connection may still have no signals for a particular harbor. Older positions are muted after two minutes and removed after ten minutes; these are display thresholds rather than guarantees about a vessel’s present location.

Read more: U.S. Coast Guard: AIS overview ↗