9.1 GMDSS introduction

The GMDSS is an internationally recognized distress and radio communication safety system for ships replacing the previous ship to ship safety system, which relied on a manual Morse code system on 500 kHz and voice radiotelephony on Channel 16 and 2182 kHz. The GMDSS is an automated ship to shore system using satellites and digital selective calling technology. The GMDSS is mandated for ships internationally by the International Maritime Organization (IMO) Safety of Life at Sea Convention (SOLAS), 1974, as amended in 1988, and carries the force of an international treaty. The procedures governing use are contained in the International Telecommunication Union recommendations and in the International Radio Regulations, and also carry the force of an International Treaty.

GMDSS CONCEPTS

• The GMDSS is specifically designed to automate a ship's radio distress alerting function, and removes the requirement for manual (ie: human) watch keeping on distress channels.
• The new system is quicker, simpler and, most importantly, more efficient and reliable than the old manual Morse Code and radiotelephone alerting systems.
• The basic concept is that Search and Rescue (SAR) authorities ashore, as well as shipping in the immediate vicinity of the ship or persons in distress will be rapidly alerted so that they can assist in a coordinated SAR operation with minimum delay.
• The new system moves the emphasis from ship-ship alerting to ship-shore alerting.
• The system also provides for urgency and safety alerting and also for the broadcast of Maritime Safety Information (weather reports and navigation warnings).

Functional requirements of the GMDSS

• The GMDSS regulations (chapter IV of the International SOLAS Convention), require that every GMDSS equipped ship shall be capable of;
• transmitting ship-to-shore Distress Alerts by at least two separate and independent means, each using a different radio communication service;
• receiving shore-to-ship Distress Alerts; transmitting and receiving ship-to-ship Distress Alerts;
• transmitting and receiving search and rescue co-ordinatingcommunications;
• transmitting and receiving locating signals;
• receiving maritime safety information;
• transmitting and receiving general radio communications relating to the management and operation of the vessel;
• transmitting and receiving bridge-to-bridge communications.

The different elements of GMDSS are as follows:

1.  INMARSAT:  It is a Satellite operated system that includes ship earth station terminals – Inmarsat B, C and F77. It provides telex, telephone and data transfer services between ship-to-ship, ship to shore, and shore to ship along with a priority telex and telephone service connected to shore rescue centres.
2.  NAVTEX is an international, automatic system for distributing maritime safety information (MSI) which includes navigational warnings, weather forecasts and weather warnings, search and rescue notices and similar information to ships.                                                                                                                                                                                         A small, low-cost and self-contained "smart" printing radio receiver is installed on the bridge, or the place from where the ship is navigated.                                                           It checks each incoming message to see if it has been received during an earlier transmission, or if it is of a category of no interest to the ship's master.                                  The frequency of transmission of these messages is 518 kHz in English, while 490 kHz is sometime used to broadcast in a local language.                                                          The messages are coded with a header code identified by the using single letters of the alphabet to represent broadcasting stations, type of messages, and followed by two figures indicating the serial number of the message.                                                                                                                                                                                                  For example: FA56 where F is the ID of the transmitting station, A indicates the message category navigational warning, and 56 is the consecutive message number
3. Emergency Position Indicating Radio Beacon (EPIRB): EPIRB is an equipment to help determine the position of survivors during a SAR operation. It is a secondary means of distress alerting. The device contains two radio transmitters, a 5-watt one, and a 0.25-watt one, each operating at 406 MHz, the standard international frequency typically signaling distress, 406MHz. •The 5-watt radio transmitter is synchronized with a GOES weather satellite going around the earth in a geosynchronous orbit. •The signal transmitted by the radio contains a unique identification number. If the weather satellite comes with an installed GPS receiver, it can detect the exact location of the transmitter of the radio signal.  It could even get information on the owner of the radio set if the EPIRB is registered. Rescue missions could thus zero in on the lost adventurer or the lost ship.  In case the EPIRB is not compatible with a GPS receiver, the geosynchronous satellite orbiting the earth can only pick only the radio signals emitted by the radio. •The location of the transmitter or the identity of the owner cannot be deduced in this case. •These satellites can only pick up trace elements of such signals and they can only give a rough idea of the location of the EPIRB. •A signal of 406MHz is treated as an emergency signal as per international standards. •The signal could help you in locating the transmitter even if it is 3 miles away. The vessel or the individual in distress could be identified if the EPIRB is registered.If an emitter transmits signals of 121.5 MHz, the rescuer or concerned party can reach the lost person even if they are at a distance of 15 miles.  •The accuracy of reaching the target could be magnified if an EPIRB also contains a GPS receiver.•The EPIRB needs to be activated to emit signals. This could be done by pushing a button on the unit, or it could happen automatically if and when it comes in contact with water.• The latter variety are known as hydrostatic EPIRB the quality makes hydrostatic EPIRBs the best choice for sailors because they could he automatically activated in case the ship or vessel meets an accident and finds itself in deep waters.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
4.  Search and Rescue Locating Equipment: Primarily the Search and Rescue Radar Transponder. This is used to home Search and Rescue units to the position of distress which transmits upon interrogation by creating a series of twelve dots on a rescuing ship's 3cm  Radar  display.                                                                                                   The detection range of the     SART is normally about 8 nautical miles.                                                                                                                                                                Once detected by radar, the   SART will produce a visual and audible indication to the persons in distress.
5.  Digital Selective Calling (DSC): This is a calling service between ship to ship, ship to shore or vice versa for safety and distress information mainly on high or medium frequency and VHF maritime radio. 
6. Inmarsat C                                                                                                                                                                                                                                                         Inmarsat C equipment is relatively small and lightweight.                                                                                                                                                                                         Antenna size of the Inmarsat C is much smaller and is omnidirectional.                                                                                                                                                          Inmarsat C being a low power system allows for its operation from the vessels emergency 24volt battery supply under emergency conditions.                                                   The omnidirectional antenna allows for a guaranteed response to a distress alert between 76 degrees North and 76 degrees South
    
7.  NAVAREA SAFETY NET     •The Inmarsat C provides ship/shore, shore/ship and ship/ship store-and-forward data and email messaging, the capability for sending preformatted distress messages to a rescue coordination center, and the Inmarsat C SafetyNET service. The Inmarsat C SafetyNET service is a satellite-based worldwide maritime safety information broadcast service of high seas weather warnings, NAVAREA navigational warnings, radionavigation warnings, ice reports and warnings generated by the USCG-conducted International Ice Patrol, and other similar information not provided by NAVTEX. SafetyNET works similarly to NAVTEX in areas outside NAVTEX coverage.                                                                                                                                                                                                                                                            Equipment vs Operational requirements

• The major difference between the GMDSS and its predecessor systems is that the radio communications equipment to be fitted to a GMDSS ship is determined by the ship's area of operation, rather than by its size.                                                                                                                                                                                                                                              The new system divides the world's oceans into 4 areas:
• Area A1 lies within range of shore-based VHF coast stations (20 to 30 nautical miles);
• Area A2 lies within range of shore based MF coast stations (excluding A1 areas) (approximately 100 - 150 nautical miles);
• Area A3 lies within the coverage area of Inmarsat communications satellites (excluding A1 and A2 areas - approximately latitude 70 degrees north to latitude 70 degrees south); and
• Area A4 comprises the remaining sea areas outside areas A1, A2 and A3 (the polar regions).
• INDIA and its surrounding SAR area are declared as Sea Area A3. There are no A1 or A2 areas in INDIA

GMDSS communication systems

• The GMDSS utilises both satellite and terrestrial            (ie: conventional) radio systems.
• Sea Area A1 requires short range radio services - VHF is used to provide voice and automated distress alerting via Digital Selective Calling (DSC).(Ch.70/156.525 MHz) alerting and radiotelephony services are available.
• Sea Area A2 requires medium range services - Medium Frequencies (2187.5 kHz) are used for voice and DSC other than Area A1
• Sea Areas A3 and A4 require long range alerting - High Frequencies (HF - 3 to 30 MHz) are used for voice, DSC and Narrow Band Direct Printing (NBDP - aka radio telex).
• Equipment requirements vary according to the area the ship is trading to or through.

Accordingly, it is quite possible that a small 300 ton cargo vessel may carry the same amount of communications equipment as a 300,000 ton oil tanker, if they are both operating in the same area....this is a marked change from the pre-GMDSS systems.

• The signals are monitored worldwide and the location of the distress is detected by non-geostationary satellites, and can be located by trilateration in combination with triangulation, respecting the varying quality of the signal received.

INMARSAT

• Very high frequency waves permit only the line of sight communication over a dependable range 30-50n.m
• Radio  waves of still higher frequencies [say, UHF or SHF frequency bands], penetrates the ionosphere and are lost in space .
• Should it be possible to reflect these waves  back to the earth by some sort of reflector, the problem of over crowding the frequency spectrum of the MF, HF, and VHF bands could be overcome.  
• DEVELOPEMENT
• The idea of putting artificial satellite in the earths orbit for just as the planets revolve round suns orbit, the artificial satellites could be made revolve round the earths  orbit
• Typical paths of an orbiting satellite could be equatorial, polar or inclined .
• if a satellite made to orbit in a equatorial at the same rate as that of axial rotation, of the earth, it will appear to be geostationary  with respect to the earth, above a fixed point of an equator.
• This is possible when a satellite is placed 35,000 km distance from the earth, in an equatorial  plane 
• The international Maritime (INMARSAT) thus placed in geo stationary orbit, remains in the same relative position to the earth, above the equator.
•  The geo stationary satellite, however, tends to drift. This necessitates a certain amount of station keeping or position control which is provided by TT&C (tracking telemetry and command) ground control station
• A communication satellite is basically an electronic package placed in a geo stationary orbit around the to aid communication from one point on the earth to another .
• Solar panels provides the required power and hydrazine gas motors help provide minor positional correction in orbit Far from being a passive relay station the satellite receives signals from the earth (up link) with the help of a number of transponder carried on board.
• The radiation pattern of the satellite antenna which determines the down link coverage on the (in accordance with the equivalent Isotropic Radiated Power –EIRP) is called the satellite footprint.
• Four satellites are placed at
• Longitudes -54 deg W(AORE-W)
• Longitudes -15deg W(AORE-E)
• Longitudes -64 deg E(IOR-E)
• Longitudes-178 deg E(IOR-E)

To provide world wide coverage

• Inmarsat of date is the only provider of world wide communication for distress sand safety purpose for general/ commercial purpose.
•  This system of communication stretches the office telephone and telex to a ship at sea sea.
• Communication originating at the office is responded at the ship’s terminal after sequential routing through local exchange international telephone network, coast earth station and the satellites.
• Aside from its commercial services, Inmarsat provides (GMDSS) to ships and aircraft at no charge, as a public service.

• Satellite systems operated by the INMARSAT, overseen by the International Mobile Satellite Organisation, (IMSO) are also important elements of the GMDSS.
• The types of INMARSAT ship earth station terminals recognized by the GMDSS are: Inmarsat B, C and F77.
• INMARSAT B and F77, an updated version of the now redundant INMARSAT A, provide ship/shore, ship/ship and shore/ship telephone, telex and high-speed data services, including a distress priority telephone and telex service to and from rescue coordination centres.                                                                                                                                The INMARSAT C provides
• ship/shore,    shore/ship and   ship/ship
• store-and-forward data and email messaging, the capability for sending preformatted distress messages to a rescue coordination center, and the Inmarsat C SafetyNET service.
• The INMARSAT C provides
• The INMARSAT C SafetyNET service is a satellite-based worldwide maritime safety information broadcast service of high seas weather warnings,
• Inmarsat C equipment is relatively small and lightweight, and costs much less than an Inmarsat B or F77 station.
• Inmarsat B and F77 ship earth stations require relatively large gyro-stabilized unidirectional antennas; the antenna size of the Inmarsat C is much smaller and is omnidirectional.
• SOLAS now requires that Inmarsat C equipment have an integral satellite navigation receiver, or be externally connected to a satellite navigation receiver.
• That connection will ensure accurate location information to be sent to a rescue coordination centre if a distress alert is ever transmitted.
• A distressed call may be intercepted at distance of
• 150 n.miles (extending upto 400 n.miles)on 2185khz MF R/T
• 30 n. Miles (extending upto 50 n.miles) on 156.8 Mhz VHF R/T
• A ship in distress may able to receive assistance only if where is another ship within range.

Regulations for Power Supplies for GMDSS equipments or radio installation as per SOLAS.

To comply with SOLAS convention, ships are required to have available a supply of electrical energy sufficient to operate the radio installations, and to charge any batteries used as part of reserve source of energy, at all times while at sea.

Emergency source of electrical energy shall be provided:-

Self contained emergency source of electrical energy shall be provided to operate VHF/ MF/ HF/ Inmarsat installation.

36 hours in case of passenger ship.

18 hours in case of cargo ship.

Reserve Source of Energy:

A reserve source of energy shall be provided to radio installation on all ships for the purpose of conducting distress / urgency and safety radio communication in the event of failure of the ship’s main and emergency source of electrical energy.

In case of main supply fail, the batteries should be able to take over automatically. The charging system must be capable of fully recharged the batteries within 10 hours. The reserve source of energy shall be adequate for at least.

01 hour for vessel constructed on or after 01st Feb 1995.

01 hours for vessel constructed before 01st Feb 1995 provided vessel fitted with emergency source of electrical energy.

Six hours for ship’s constructed before 01st  Feb 1995,  if vessel is not provided with emergency source of electrical energy. 

In Compliance with Solas Ch-IV, Reg 13 (Gmdss Batteries Requirement)

A reserve source or sources of energy other than Ship’s main and Emergency sources of electrical power shall be capable of operating GMDSS equipment’s for:

(a) 1 h on ships provided with an emergency source of electrical power

(b) 6 h on ships not provided with an emergency source of electrical power

Note: The reserve source energy should also power emergency lighting fitted in the GMDSS console (reg 6.2.4)

Battery Charger:

When a means of automatically charging GMDSS batteries is provided , it should be capable of recharging them to minimum capacity requirements within 10 h.

The following formula is recommended for determining the electrical load to be supplied by the reserve source of energy for each radio installation required for distress conditions= 1/2 of the current consumption necessary for transmission + the current consumption necessary for reception + the current consumption of any additional loads.

Testing of GMDSS Batteries:

a. CAPACITY TEST: The capacity of the battery or batteries shall be checked, using an appropriate method, at intervals not exceeding 12 months, when the ship is not at sea. Same should be recorded in GMDSS log book.

b. Monthly/Weekly : Switch off the AC power to GMDSS and operate the GMDSS for 1 hour (or 6 hours) to see if it can operate for around that time.

c.  Daily On load/Off load test of the batteries. Mention the voltage for the same in the Gmdss log book.

THE OVERALL SYSTEM

The Inmarsat system has three major components:

• 1. The Space Segment provided by Inmarsat
• 2. The Ground Segment provided by signatories.
• 3. The Ship Earth Station.

SPACE SEGMENT  Four geo stationary satellites serve ocean regions designated as  AOR(E), POR AND IOR and AOR(W)        Four spare satellites are also provided to serve as back-ups.

Ground segment

• Telemetry, Tracking and Command station (TT&C) Control the positionof the satelliteThey linked with the SCC located at London.
• Satellite Control centre. (SCC) Tracks the exact position of the satellites andtransmits appropriate signals to TT&C station
• Network Control Centre. (NCC) ) Monitor and co-ordinate the activities of the network.It is located close to the SCC located at London.
• Operations control centre. (OCC) It is the nerve centre of the INMARSAT sys.Control the whole network of fixed station, mobile stations and satellites and located at London. The OCC is responsible for the commissioning of  Ships Earth Station (SES)                                                                                                                                              ESSENTIAL FUNCTION OF THE NCS ARE
• To monitor distress priority request – should the CES not respond to distress priority requests, the NCS would itself take appropriate action
• To transmit TDM carrier- to monitor, control, and co-ordinate the operation and allocation of the channels to each CES and SES.
• To assign only telephone channels
• To control and monitor both telex and telephone channels.
• To transmit ALL Ship’s announcement Each NCS interacts with the CES in its Ocean Region and other NCS as well as the enabling mutual transfer of information throughout the system.
• THE COAST EARTH STATION                   
• The Coast Earth Station provides the link between the satellites and terrestrial communication network
• It has a 11-14 metre parabolic (Cassegrain) dish antenna.
• It operate in  C(6Ghz and14Ghz) band for transmission of signal to from the satellite.
• It also operates in the L (1.6Ghz and 1.5 Ghz) band transmission and reception of network control signals.
• The Network Co-ordination Station (NCS)
• The NCS is provided one for each service- in each Ocean region.
• SHIP EARTH STATION
• SES or MES consist of
• The above deck equipment (ADE) consisting of the antenna unit
• The below deck equipment (BDE) consisting of the transceiver unit, with VDU, keyboard, printer, and interfaces for telex, telephone and fax.
• CHANNEL ASSIGNMENT
• In order to receive and send channel assignment, the Mobile Earth Stations and Coast Earth Stations monitor the NCS on the common signalling channels termed Time Division Multiplex (TDM)
• channels- TDM-0 or TDM-1.
• Each  TDM in turn consist of 22 time slots to permit multiplexed or shared use of the same TDM channel.
• The SES in time division multiplex access (TDMA) is assigned a corresponding time slot during which it has access to the satellite.
• OPERATIONAL PROCEDURE
• Since the satellite communication is line of a sight communication, the satellite in principle has to be acquired i.e the antenna of the user equipment must be aligned i.e pointing to the satellite at all times to maintain communication.
• The acquisition is achieved when, the user equipment antenna locks on to the satellite signals i.e. Common Signalling Channel (CSC) and the signal strength is sufficient to track the satellite. Ship's heading is necessary for the antenna tracking system.
• Based on the vessel's position, every ship could be in the foot print of one, two or three satellites, In order to acquire the satellite, azimuth and elevation charts or maps or information tables which are ready available.
• The azimuth and elevation of the satellite A  antenna are adjusted to point the antenna to the satellite.
• The antenna beam width is wide enough to enable coarse acquisition of the satellite.
• The electronic step track circuitry in the equipment does the necessary finer alignment to obtain a strong enough signal to track and lock and look on to the satellite.
• The entire acquisition program can be automatically achieved at the time of switching on although it may take several minutes to be fully acquired.
• Sufficient care should be exercised to ensure acquisition of the desired satellite in over-lapping ocean areas.
• INMARSATSAT STANDARD ‘C’
• It consist of
• The ADE called External Mounted Equipment (EME)
• It is made up of Data Circuitry Terminal Equipment (DCE)
• The DCE interfaces the SES, with its transmitter/receiver/omni directional antenna having no moving parts, to the satellite system.
• The below deck equipment called Internal Mounted Equipment (IME)
• It is made up of the Data Terminal Equipment(DTE)
• The DTE interfaces external inputs/outputs devices viz. Keyboard, screen and printer for message processing to the SES.
• An external computer (Laptop or desktop) complete with its own peripherals serving as a multi-tasking computer ,may also be used.
• Inmarsat A
• The original Inmarsat system, which was withdrawn from service at the end of 2007.
•  Based on analogue techniques, it provided global two-way telephony, facsimile, data and telex communications to the maritime community for a quarter of a century.
• Inmarsat B
• The first digital successor to Inmarsat A, capable of high-quality telephony, facsimile, data and telex services, and compatible with the Global Maritime Distress and Safety System (GMDSS).
• Inmarsat C and Mini C
• A digital system based on a low-cost satellite terminal, providing two-way store-and-forward messaging, distress calling, EGC SafetyNET™ and FleetNET™, data reporting and polling.
• The system is approved for use under the (GMDSS) and mandatory for Solas-compliant ships operating outside Navtex coverage areas.
• Inmarsat M
• The first briefcase satphone, introduced in 1993.
• Also available in the maritime market, as a smaller, digital alternative to Inmarsat B, offering two-way voice telephony, distress alerting, fax and data services at lower data rates.
• Mini M
• Introduced in 1995, based on digital technology and capable of two-way voice telephony, alerting, fax and data services.
• Operates only in the reduced coverage offered by the Inmarsat-3 spot beams, but its notebook size has made it one of the most popular Inmarsat services on land and at sea.
• What are the advantages of the GMDSS over the former system?
• provides worldwide ship to shore alerting, it is not dependent upon passing ships
• simplifies radio operations, alerts may be sent by "two simple actions"
• ensures redundancy of communications, it requires two separate systems for alerting
• enhances search and rescue, operations are coordinated from shore centers
• minimizes unanticipated emergencies at sea, Maritime Safety Information (MSI) broadcasts are included
• eliminates reliance on a single person for communications, it requires at least two licensed GMDSS radio operators and typically two maintenance methods to ensure distress communications capability at all times.