What to check on a Inmarsat Terminal.
Navigation instruments like the GNSS receiver or echo sounder tell the bridge about the ship's own situation. An Inmarsat terminal connects the ship to the outside world, and where fitted for Inmarsat-C, it is one of the recognized GMDSS systems for sending and receiving distress alerts, urgency and safety messages, and MSI broadcasts, entirely independent of VHF or MF/HF range limits. FleetBroadband and higher-bandwidth Inmarsat services add voice and data connectivity for operational and crew welfare traffic, but the GMDSS function is the part that carries a strict carriage requirement.
What sets an Inmarsat terminal apart
Navigation instruments like the GNSS receiver or echo sounder tell the bridge about the ship's own situation. An Inmarsat terminal connects the ship to the outside world, and where fitted for Inmarsat-C, it is one of the recognized GMDSS systems for sending and receiving distress alerts, urgency and safety messages, and MSI broadcasts, entirely independent of VHF or MF/HF range limits. FleetBroadband and higher-bandwidth Inmarsat services add voice and data connectivity for operational and crew welfare traffic, but the GMDSS function is the part that carries a strict carriage requirement.
Main components
Above-deck unit
A radome-enclosed antenna, either omnidirectional for Inmarsat-C or a stabilized tracking antenna for FleetBroadband, mounted with clear sky view fore, aft and to both sides.
Below-deck unit
The transceiver and terminal processing unit, connected to the ship's power supply with battery backup, and interfaced to the GMDSS console for distress alerting.
Subscription and network
Service runs through a Land Earth Station and requires an active service subscription; a terminal with lapsed subscription is functionally equipment without a network, whatever its physical condition.
Selection and sizing
The choice between Inmarsat-C (low bandwidth, message-based, mandatory GMDSS function) and FleetBroadband or higher-tier services (broadband voice and data) depends on the vessel's communication needs beyond the regulatory minimum. Redundancy matters for the GMDSS function specifically: many vessels carry the Inmarsat-C terminal as one of two or more independent means of distress alerting required by the vessel's sea area classification.
Regulations and class requirements
SOLAS Chapter IV sets the GMDSS carriage requirements by sea area (A1 through A4), and Inmarsat-C satisfies the requirement for sea areas A1 through A3. Equipment must carry GMDSS type approval, and the interface to the EPIRB and DSC alerting systems is checked during survey. Regular testing of the distress alert function, without actually transmitting a live distress, is part of the vessel's routine drill schedule.
Typical faults
- Radome cracking and water ingress into the above-deck unit, causing corrosion of the antenna electronics that shows up as intermittent signal loss.
- Low-noise amplifier failure in the antenna assembly, degrading receive sensitivity long before it fails completely.
- Firmware or software faults in the terminal unit that require a factory reset or manufacturer intervention to clear.
- Lapsed service subscription, often discovered only when the crew tries to send a message and gets no network response.
- Below-deck unit power supply or battery backup failure, leaving the terminal without power during a mains interruption.
What to look for in a supplier
- Current GMDSS type approval matching the terminal's role in the vessel's radio installation.
- Confirmed Land Earth Station coverage for the trading area the vessel actually operates in.
- An established technical support network able to diagnose faults remotely before committing to a port call for repair.
- Spare above-deck unit components (radome, LNA) that do not require replacing the entire antenna assembly for a minor fault.
Check the subscription status before troubleshooting the hardware; a terminal in perfect working order is silent if the service behind it has lapsed.