Marine Communications, GMDSS and ECDIS
GMDSS
Sea area A1 is within VHF coast station coverage, A2 within MF, A3 within Inmarsat coverage and A4 the remaining polar regions; carriage requirements scale with the area. Know the equipment for your ship: DSC on VHF channel 70, NAVTEX on 518 kHz international (490 and 4209.5 kHz national), Inmarsat-C, 406 MHz EPIRB with 121.5 MHz homing, and the 9 GHz SART, detectable by a large ship's radar at about 5 nm and much less by small craft. Understand distress, urgency and safety priority, MAYDAY RELAY, and the false alert cancellation procedure. The reserve source of energy must be tested and recorded.
ECDIS
The ENC is the primary chart; RCDS is a fallback with limitations. Know safety contour, safety depth, safety settings, the display modes, route planning and route checking, look-ahead, alarms and the requirement for an independent back-up arrangement. CATZOC indicates data quality; the Admiralty Information overlay adds temporary and preliminary notices. A type-approved ECDIS using up-to-date ENCs satisfies chart carriage.
Trap: assuming ECDIS removes the need for an independent back-up, and setting the safety contour to the ship's draft instead of a safe navigable depth.
Rule of thumb: check scale, CATZOC and safety settings before every route is used, not just when it is planned.