Marine Glossary

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INMARSAT

Acronym for International Maritime Satellite, it is the name of the satellite system operated by Inmarsat Corporation, a consortium of communications companies from the world's major shipping countries with about 64 members. It was founded in 1982 and provides satellite communications between vessels and land based public telephone lines worldwide as well as providing communications for the Global Marine Distress and Safety System. The U.S. member and primary operator of INMARSAT is the U.S. Comsat Corporation.

There are several services available:

INMARSAT-A is the original system for voice and data transmissions. Communications cost about 5 dollars per minute plus land line long distance charges as well as set up and monthly service charges. The antenna are the 4-foot white spheres (weighing some 200 pounds) that are often seen on large commercial vessels.

INMARSAT-B uses the same equipment but with digital technology for improved performance. A and B systems are in the 50 to 75k$ range.

INMARSAT-C is much smaller and less expensive but is restricted to data only, no voice. These text messages are sent and received like SITOR except that the messages go by satellite communications as opposed to HF radio. The required antenna is the size of a football; equipment costs for the most basic system is about 5k$, which makes this relatively more feasible for smaller vessels desiring the convenience of satellite communications along with GMDSS services (SafetyNet uses INMARSAT-C). Power drain is about 10 watt on standby and 100 watt when transmitting.

INMARSAT-M is the latest development with equipment and services first appearing in 1994. This system is an improved version of the earlier A and B systems for both digitized voice and data transmission. Equipment costs will be between 15 to 25k$ with on-line charges of about 4 dollars per minute plus land charges. The antenna are about 2 feet in diameter and weigh about 50 pounds. Standby power consumption, however, is high for auxiliary sailing vessels at some 100 to 180 watts. Data transmission is at 2400 baud.