In the Inmarsat system there are many types of different equipment and systems in use. The Inmarsat equipment normally consists of a transceiver and an antenna. What equipment is attached to the transceiver will depend on the type of Inmarsat system: this could be a computer with monitor and printer, a telephone handset, a fax or a TELEX modem.

We recognize the GMDSS-approved systems and non-GMDSS systems.

GMDSS-approved systems

The systems with GMDSS approval are:

• Inmarsat B.
• Inmarsat C.
• Inmarsat Fleet 77, also called F77.

With these systems is it possible to send a Distress Alert within the GMDSS system. The Inmarsat C system is also used for the transmission/reception of Maritime safety Information (MSI) within the GMDSS system. The systems with the GMDSS approval should comply with the relevant IMO regulations concerning the GMDSS equipment.

The Inmarsat B and F 77 are systems that are using parabolic dish antennae. These antennae are placed in a dome. In this dome it will be possible to move the dish antenna. It can rotate horizontally and vertically, which is necessary so as to bring the dish antenna into the right position, i.e. pointing it at the prefered Inmarsat satellite. During the movements of the vessel, the dish antenna will move to keep it pointed at the satellite. These complex antenna systems are large and heavy and not always easy to install.
With these systems it is possible to use: phone, TELEX, fax, e-mail, data transfer and internet.
The costs of these ISDN connections are calculated based on time of duration of the connection between ship and (via a LES) contacted user. If the MPDS (with MPDS = Mobile Packet Data Service, the terminal will be "on line") function of the F 77 has been used, the costs will be calculated based on the amount of data transferred.


The Inmarsat C system uses an omnidirectional antenna. As this antenna transmits and receives in all directions, there is no need to point it in
the direction of the satellite. This antenna system is quite simple, isn't heavy and is easy to mount. This makes it much cheaper compared to the complex antenna righting system of the Inmarsat B and F77 terminals. The signal strength of this Inmarsat C system is weaker than the other mentioned systems. Because of this 'weak signal strength', you cannot work 'on line' with the Inmarsat C system. This system will always work 'store and forward' - this will be explained later in this chapter. Inmarsat C can be used e.g. for sending faxes, sending/receiving e-mails and TELEX, but not for making phone calls. The cost of sending a message will be calculated based on the total number of bytes that have been transferred.

Non-GMDSS systems

Non-GMDSS systems are:

• Inmarsat M.
• Inmarsat mini M.
• Inmarsat Fleet 33 and 55 (F33 and F55).
• Inmarsat broadband.

With these Non-GMDSS systems it is possible to use: phone, fax, e-mail, data transfer and internet.