Describe the Inmarsat-C system — what it can do, how the distress alert works, and what SafetyNET provides.

A. INMARSAT-C SYSTEM: Inmarsat-C is a maritime satellite communication terminal (Low Data Rate — approximately 600 bps) providing TWO-WAY data communication (not voice) via Inmarsat GEO satellites. CAPABILITIES: (1) TEXT MESSAGE TRANSMISSION: send/receive telexes and text messages to any telex/email address; (2) DISTRESS PRIORITY: dedicated distress button transmits a priority distress message directly to the relevant MRCC via the Inmarsat Land Earth Station (LES). Position from GPS is automatically included; (3) SafetyNET: INMARSAT'S MSI BROADCAST SERVICE: SafetyNET is the Inmarsat equivalent of NAVTEX for ocean areas. The MRCC/navwarning authorities broadcast Maritime Safety Information (navigational warnings, meteorological warnings, MSI for ocean areas beyond NAVTEX range) via SafetyNET EGC (Enhanced Group Calling). The Inmarsat-C receiver automatically receives and prints SafetyNET messages relevant to the vessel's sea area; (4) LRIT INTERFACE: Inmarsat-C is often the transport layer for LRIT (Long Range Identification and Tracking) position reporting; (5) POLLING: port state authorities and flag states can "poll" the vessel via Inmarsat-C to determine position; OOW DUTIES: (a) Ensure Inmarsat-C is powered and logged into the satellite; (b) Read and act on SafetyNET messages as they arrive; (c) Know the location of the distress button (typically a dedicated key on the terminal); (d) Test the terminal according to the maintenance schedule.

B. Inmarsat-C provides voice calls, fax, and high-speed data to vessels. It is used for all commercial communications and has no special distress function.

C. SafetyNET messages are only received by vessels registered with the IMO. Vessels without IMO numbers cannot receive SafetyNET broadcasts.

D. Inmarsat-C only works within 200nm of land. For ocean areas, HF radio is the primary communication system.

A. DSC DISTRESS ALERT — VHF PROCEDURE: DSC (Digital Selective Calling) on VHF Channel 70 is the primary GMDSS distress alerting mechanism. PROCEDURE: (1) ENSURE POSITION IS UPDATED: the DSC controller must have a current GPS position input (most modern sets auto-update from GPS). Verify the position shown is current; (2) OPEN THE DSC CONTROLLER: navigate to the distress function — typically a protected button (lift cover or press and hold to prevent accidental activation); (3) SELECT NATURE OF DISTRESS: most DSC controllers allow selection of distress nature — UNDESIGNATED, FIRE, FLOODING, COLLISION, GROUNDING, LISTING, SINKING, DISABLED AND ADRIFT, ABANDONING SHIP. If time permits, select the correct nature; (4) TRANSMIT: press/hold the distress button for the required duration (typically 5 seconds with button confirmation). The controller transmits the DSC distress call on Ch 70 — this broadcasts your MMSI, position, time, nature of distress to all vessels in range and to coast stations; (5) SWITCH TO CH 16: immediately after DSC transmission, switch VHF to Ch 16 and transmit the voice MAYDAY message; (6) MAYDAY VOICE: "MAYDAY MAYDAY MAYDAY — THIS IS [vessel name × 3] — MAYDAY [vessel name] — POSITION [lat/lon] — [NATURE OF DISTRESS] — [POB] — [ANY OTHER RELEVANT INFO] — OVER"; (7) AWAIT ACKNOWLEDGEMENT: coast stations and vessels will acknowledge on Ch 16.

B. The DSC distress alert is transmitted on Ch 16. Tune the VHF to Ch 16, press the distress button, and speak the MAYDAY message directly.

C. Voice MAYDAY on Ch 16 must be transmitted first — then the DSC alert follows. The voice call alerts nearby vessels who may not be monitoring DSC.

D. DSC distress is only for MF/HF radio. VHF uses the traditional voice MAYDAY on Ch 16 only — VHF DSC is not a required GMDSS function.

A. NAVTEX — SYSTEM AND OOW USE: NAVTEX (Navigational Telex) is an automated system that broadcasts maritime safety information (MSI) on 518 kHz (international) and 490 kHz (national language) using NBDP (Narrow Band Direct Printing). WHAT IT PROVIDES: (1) NAVIGATIONAL WARNINGS (B messages): hazards to navigation — wrecks, buoy off station, new obstructions, pilot areas, lights changed; (2) METEOROLOGICAL WARNINGS (W messages): gale warnings, storm warnings, weather bulletins; (3) PILOT SERVICE MESSAGES (P messages); (4) ICE REPORTS (I messages); (5) SAR INFORMATION (D messages): distress messages, SAR operations in the area; (6) SUBFACTS and NAVFACTS: submarine exercise areas and other military notifications. HOW IT WORKS: NAVTEX stations broadcast on a schedule. Each station has a unique letter identifier. The NAVTEX receiver is programmed to receive messages from stations covering your sea area. Messages not relevant to the vessel's area can be filtered. OOW DUTIES: (1) Ensure NAVTEX is switched on and printing; (2) Check the NAVTEX receiver is set to receive messages from stations in the current sea area; (3) READ ALL MESSAGES as they print; (4) Bring significant messages (navigational warnings, gale warnings, SAR in the area) to the master's attention; (5) CHART PLOT: plot navigational warnings on the chart/ECDIS; (6) Do NOT ignore NAVTEX messages — they contain safety-critical information.

B. NAVTEX operates on VHF Ch 68 and provides local port information for vessels within 20nm of the coast. It is only relevant when approaching port.

C. NAVTEX is a backup to weather fax and provides only meteorological information. Navigational warnings are only available through the vessel's AIS.

D. NAVTEX messages should be collected and reviewed once per watch. Urgent messages are highlighted in red and require immediate action; all others can wait.