Nautical Institute Dynamic Positioning (DP) Revalidation and CPD Program Practice Exam

In an HPR system, a Responder Beacon is an underwater acoustic transponder. Its job is to listen for an interrogation signal sent through the water, and then reply back through the water with its own encoded acoustic signal. This underwater two-way communication allows the DP system to measure range and/or bearing to the beacon, helping determine the vessel’s position relative to a set of known beacons on the seafloor or anchored in the water.

Communicating through water is essential here because the system relies on hydroacoustic signals traveling underwater, not radio or air-based signals. A device that communicates through the air would not participate in the underwater timing and signaling the HPR relies on. A signal transmitter on the surface describes something that sends signals from above, not the underwater responder. A general navigational aid for emergencies is too vague to define the precise role of these beacons. Therefore, the description of being interrogated through water and replying through water best matches how a Responder Beacon operates in an HPR system.