Inmarsat FleetBroadband

What sets FleetBroadband apart

FleetBroadband (FB) is a broadband IP satellite terminal running over Inmarsat's I-4 satellite constellation, offering simultaneous voice, data and standard IP connectivity at up to a few hundred kilobits per second depending on terminal class. That is a different class of service from Inmarsat-C, which is a narrowband, store-and-forward messaging terminal with no real-time voice or IP capability. FleetBroadband is not itself a GMDSS-mandated terminal in the way Inmarsat-C or an MF/HF set is — it is normally fitted for commercial communication, crew welfare and operational data, though some FB terminals do carry an approved distress priority function.

Main components

Above-deck unit (ADU)

A stabilised antenna, typically 30 to 60 cm depending on terminal class such as FB150, FB250 or FB500, that tracks the geostationary satellite through the ship's roll and pitch.

Below-deck unit (BDU)

Houses the modem, handles call and session management, and provides the Ethernet, ISDN and telephone interfaces used by the ship's office and crew systems.

SIM and airtime subscription

FB uses a SIM-based subscription through an Inmarsat service provider, with data typically billed by volume and voice by the minute, separate from any VSAT contract the ship may also carry.

Distress priority function

Where fitted and activated, gives voice calls a priority marking recognised by the Inmarsat network and rescue coordination centres, though this is an addition to, not a replacement for, the ship's mandatory GMDSS equipment.

Selection / Sizing

Regulations / Class

FleetBroadband is not a SOLAS carriage requirement in itself. Where it is fitted with an activated distress priority service and the flag administration accepts it as part of the GMDSS fit, it must be documented on the Safety Radio Certificate; otherwise it sits outside GMDSS survey scope and is treated as commercial equipment. Class societies have no periodic survey requirement for FB terminals unless the owner has specifically notated the installation.

Typical faults

• Antenna radome cracked and taking on water — intermittent tracking loss that looks like a software fault until the radome is opened.
• Subscription lapsed or data cap exceeded without the crew being told — terminal shows connected but sessions time out.
• ADU cabling run too close to radar or VSAT feeds — intermittent interference that is hard to diagnose without swapping cable routes.
• Firmware left unpatched for years — known stability bugs in call handling persist because nobody schedules the update.

What to look for in a supplier

• Confirms terminal class against actual bandwidth need rather than defaulting to the largest antenna.
• Offers airtime plans with clear data caps and overage terms, not just a headline per-megabyte rate.
• Can support firmware updates remotely without requiring a service call for every minor revision.

Do not let FleetBroadband's distress priority feature be treated by the crew as equivalent to the ship's mandatory GMDSS terminal — it is a convenience layer on top of, never a substitute for, Inmarsat-C or MF/HF DSC.