Choose your study region

Choose a course collection, not your nationality. Changing region does not change your courses, progress or access.

Compass network home

Optional preference saved in this browser on Compass Revision. It does not sync between devices or the separate course websites. You are never redirected automatically.

All questions
Marine radio

What may safely be concluded from an AIS display with no target at the harbour entrance?

Short answer

Only that no received AIS report currently creates a displayed target

AIS data may be absent, delayed or wrong, and some vessels do not transmit it. Use AIS as one source alongside lookout and all available means.

Sources and scope

Reviewed by Richard Moore on . This answer is scoped to united kingdom marine vhf and internationally harmonised procedure; check the current chart, publication, local rules and official operational guidance before acting afloat.

Quick check

What may safely be concluded from an AIS display with no target at the harbour entrance?