HF DSC alert with no acknowledgment: what does a yacht do 400 nm off Portugal?
At 18:10 UTC, the 24 m sail-training yacht Aurora (12 persons, MMSI 247654321) is on passage in position 38°40′N 020°10′W, about 400 nm west of Cabo da Rocha. The yacht is equipped with an MF/HF DSC and NBDP installation, an Inmarsat-C terminal that is currently logged out for maintenance, and VHF. The MF/HF watch is kept on the 8 MHz DSC distress frequency 8 414.5 kHz. A DSC distress alert is received from a 30 m motor vessel 250 nm to the north-west: nature of distress 'fire', telecommand 'radiotelephony', and a position that looks consistent with the received signal. No coast station acknowledgment is heard within five minutes. The yacht can make 9 kn; the wind is north-east force 5. The operator must decide whether to acknowledge, which frequencies to use, and how to avoid blocking a coast station that may be about to respond.
1. Should Aurora acknowledge the DSC distress alert? Give the decision and the reasoning.
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Aurora should first listen on the paired radiotelephony frequency, 8 291 kHz, and check whether a coast station or another ship has already acknowledged. If there is no acknowledgment and Aurora is in a position to assist, it should acknowledge the alert rather than remain silent. The DSC acknowledgment is sent on the same DSC distress frequency, 8 414.5 kHz, using the distress-acknowledgment function with Aurora’s MMSI and the distressed vessel’s MMSI. It is not a distress relay and must not be sent as an 'all ships' call. The reason for acting is that a DSC alert that is not acknowledged may leave the casualty without a confirmed response; a ship that can assist should not assume that a coast station has received the alert. If another station acknowledges first, Aurora should not duplicate the acknowledgment, but should keep watch on 8 291 kHz and be ready to assist.
2. Set out the frequency and message sequence Aurora should use after the alert, including the role of NBDP.
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After sending the DSC acknowledgment on 8 414.5 kHz, Aurora should switch to the paired radiotelephony distress frequency 8 291 kHz and call the distressed vessel. A short initial call should identify Aurora, state that the DSC alert has been acknowledged, give Aurora’s position and course, and ask for the nature of distress, persons on board, and whether assistance is required. If voice contact is established, the detailed traffic should stay on 8 291 kHz or on a working frequency assigned by a coast station. NBDP on 8 376.5 kHz is the paired telex frequency; it is useful for sending a written distress message or detailed information when voice is unreliable, but it should not be used before the initial DSC and radiotelephony attempt. The DSC watch on 8 414.5 kHz should continue. The operator should not use 8 414.5 kHz for voice, because that would interfere with DSC distress traffic.
3. No reply is received after ten minutes. What should Aurora do next, and what propagation and operational factors should influence the choice?
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Aurora should not abandon the incident after ten minutes. It should try again on 8 291 kHz with a distress message that includes the distressed vessel’s DSC details and Aurora’s ability to assist. It should also consider shifting to the 12 MHz band, using DSC 12 577 kHz and radiotelephony 12 290 kHz, if the 8 MHz band appears poor or if a coast station is more likely to keep a 12 MHz watch. At 18:10 UTC and 250–400 nm, 8 MHz is often usable, but ionospheric conditions, time of day and antenna efficiency matter. Aurora should inform a coast station by the most reliable available means, keep the DSC watch, set a course to close the casualty if that is safe, and log all times and frequencies. NBDP on 8 376.5 kHz can be used to send a written distress message if voice remains unanswered. The yacht must also maintain its own navigation and safety watch while assisting.