Course Topics

  • 3.1 Operation of all Internal Communication Systems on Board
  • 3.2 Technical Films Viewing & Discussion

3.1 Operation of all Internal Communication Systems on Board



Global Maritime Distress and Safety System (GMDSS)

Ship distress and safety communications entered a new era on 1st February 1999 with the full implementation of the Global Maritime Distress and Safety System (GMDSS) - an integrated communications system using satellite and terrestrial radio communications to ensure that no matter where a ship is in distress, aid can be dispatched.

The GMDSS was developed by the International Maritime Organization (IMO), the specialized agency of the United Nations with responsibility for ship safety and the prevention of marine pollution, in close co-operation with the International Telecommunication Union (ITU) and other international organizations, notably the World Meteorological Organization (WMO), the International Hydrographic Organization (IHO) and the COSPAS-SARSAT partners.

Under the GMDSS, all passenger ships and all cargo ships over 300 gross tonnage on international voyages have to carry specified satellite and radio communications equipment, for sending and receiving distress alerts and maritime safety information, and for general communications. The regulations governing the GMDSS are contained in the International Convention for the Safety of Life at Sea (SOLAS), 1974.

The GMDSS requirements are contained in Chapter IV of SOLAS on Radio communications and were adopted in 1988. The requirements entered into force on 1 February 1992 but provided for a phase-in period until 1 February 1999.




The Automatic Identification System (AIS) is an automatic tracking system used for collision avoidance on ships and by vessel traffic services (VTS). When satellites are used to detect AIS signatures, the term Satellite-AIS (S-AIS) is used. AIS information supplements marine radar, which continues to be the primary method of collision avoidance for water transport.

Information provided by AIS equipment, such as unique identification, position, course, and speed, can be displayed on a screen or an ECDIS. AIS is intended to assist a vessel's watch standing officers and allow maritime authorities to track and monitor vessel movements. AIS integrates a standardized VHF transceiver with a positioning system such as a GPS receiver, with other electronic navigation sensors, such as a gyrocompass or rate of turn indicator. Vessels fitted with AIS transceivers can be tracked by AIS base stations located along coast lines or, when out of range of terrestrial networks, through a growing number of satellites that are fitted with special AIS receivers which are capable of deconflicting a large number of signatures.

The International Maritime Organization's International Convention for the Safety of Life at Sea requires AIS to be fitted aboard international voyaging ships with 300 or more gross tonnage (GT), and all passenger ships regardless of size.



Voyage Data Recorder, or VDR, is a data recording system designed for all vessels required to comply with the IMO's International Convention SOLAS Requirements (IMO Res.A.861(20)) in order to collect data from various sensors on board the vessel. It then digitizes, compresses and stores this information in an externally mounted protective storage unit. The protective storage unit is a tamper-proof unit designed to withstand the extreme shock, impact, pressure and heat, which could be associated with a marine incident (fire, explosion, collision, sinking, etc.).

The protective storage unit may be in a retrievable fixed unit or free float unit (or combined with EPIRB) when the ship sinks in a marine accident. The last 12 hours (48 Hours for the 2014 regulations MSC.333(90)) of stored data in the protected unit can be recovered and replayed by the authorities or ship owners for incident investigation. Besides the protective storage unit, the VDR system may consist of a recording control unit and a data acquisition unit, which are connected to various equipment and sensors on board a ship. The new MSC.333(90) regulations also state a minimum of 30 days of recorded data must be held internally (this could be within the recording control unit, data acquisition unit, Main Electronics Unit depending on the manufacturers terminology).

Although the primary purpose of the VDR is for accident investigation after the fact, there can be other uses of recorded data for preventive maintenance, performance efficiency monitoring, heavy weather damage analysis, accident avoidance and training purposes to improve safety and reduce running costs.




Maritime Mobile Service Identity (MMSI) is a series of nine digits which are sent in digital form over a radio frequency channel in order to uniquely identify ship stations, ship earth stations, coast stations, coast earth stations, and group calls. These identities are formed in such a way that the identity or part thereof can be used by telephone and telex subscribers connected to the general telecommunications network to call ships automatically




An Electronic Chart Display and Information System (ECDIS) is a geographic information system used for nautical navigation that complies with  International Maritime Organization (IMO) regulations as an alternative to paper nautical charts. 



A marine radar with Automatic Radar Plotting Aid (ARPA) capability can create tracks using radar contacts. The system can calculate the tracked object's course, speed and closest point of approach (CPA), thereby knowing if there is a danger of collision with the other ship or landmass.



Navtex (Navigational Telex) is an international automated medium frequency direct-printing service for delivery of navigational and meteorological warnings and forecasts, as well as urgent maritime safety information to ships.

Navtex was developed to provide a low-cost, simple, and automated means of receiving this information aboard ships at sea within approximately 370 km (200 nautical miles) off shore.

Navtex is a component of the International Maritime Organization/International Hydrographic Organization Worldwide Navigation Warning Service (WWNWS). Navtex is also a major element of the Global Maritime Distress Safety System




Marine VHF radio refers to the radio frequency range between 156.0 and 174 MHz, inclusive. The "VHF" signifies the very high frequency of the range. In the official language of the International Telecommunication Union the band is called the VHF maritime mobile band. In some countries additional channels are used, such as the L and F channels for leisure and fishing vessels in the Nordic countries (at 155.5–155.825 MHz).

Marine VHF radio equipment is installed on all large ships and most seagoing small craft. It is also used, with slightly different regulation, on rivers and lakes. It is used for a wide variety of purposes, including summoning  rescue services and communicating.

A marine VHF set is a combined transmitter and receiver and only operates on standard, international frequencies known as channels. Channel 16 (156.8 MHz) is the international calling and distress channel. Transmission power ranges between 1 and 25 watts, giving a maximum range of up to about 60 nautical miles (111 km) between aerials mounted on tall ships and hills, and 5 nautical miles (9 km; 6 mi) between aerials mounted on small boats at sea level. Frequency modulation (FM) is used, with vertical polarization, meaning that antennas have to be vertical in order to have good reception.

Modern-day marine VHF radios offer not only basic transmit and receive capabilities. Permanently mounted marine VHF radios on seagoing vessels are required to have certification of some level of "Digital Selective Calling" (DSC) capability, to allow a distress signal to be sent with a single button press.




An anemometer is a device used for measuring the speed of wind, and is also a common weather station instrument. The term is derived from the Greek word anemos, which means wind, and is used to describe any wind speed measurement instrument used in meteorology.




Echo Sounding is a type of sonar used to determine the Depth of water by transmitting sound pulses into water. The time interval between emission and return of a pulse is recorded, which is used to determine the Depth of water along with the speed of sound in water at the time.

Doppler / Speed Log is an instrument, used in ships, to measure ship's relative speed with water (in which it is traveling) by the use of Doppler effects on transmitted / reflected sound waves.




Gyrocompass is a type of non-magnetic compass which is based on a fast-spinning disc and the rotation of the Earth (or another planetary body if used elsewhere in the universe) to find geographical direction automatically.

 Gyrocompasses are widely used for navigation on ships, because they have two significant advantages over magnetic compasses

* They find true north as determined by the axis of the Earth's rotation, which is different from, and navigationally more useful than, magnetic north, and

* They are unaffected by ferromagnetic materials, such as in a ship's steel hull, which distort the magnetic field.