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U.S. Ship: Please divert your course
15
degrees to the north to avoid a collision.
Canadian: Recommend you divert YOUR course 15 degrees.
U.S.: This is the captain of a
U.S.Navy
ship. I say again, divert your course.
Can.: No. I say again, divert YOUR course.
U.S.: This is an aircraft carrier of
the
U.S. Navy. We are a large warship. Divert your course now!
Can.: This is a lighthouse. Your call . . .
(former
Navy: U.S.N. Radioman,
Signalman, Quartermaster)
The
advances in maritime electronics systems over the last 10 years have
nothing short of spectacular with the world of marine communications
and navigation seemingly destined to a total reliance on
satellites.
NAVSTAR Global Positioning System
(GPS) service is fully operational, and GPS equipment prices have
literally plunged to consumer electronics levels. INMARSAT
has
most
commercial and large pleasure vessels equipped with satellite
communications. IRIDIUM although promising
is now in financial difficulties, and SSB shore stations have largely
ceased in most main western countries. The
Global Maritime Distress and Safety System (GMDSS) is now operational
with far reaching ramifications to all yacht owners. It is a current
subject of debate with respect to equipment suitability and prices for
yachts, and equipment is now available to allow yachts to plug into the
system. There are many commentators who
seem to misunderstand the magnitude and complexity of the system as it
is implemented, which unfortunately increases the confusion.
The one inherent danger of course is
that many people are sailing away without the knowledge to maintain the
equipment, understand how to use it properly, and worse still without
the skills to cope when the systems fail. All these high
technology systems are in the end only aids to navigational for use in
conjunction with properly corrected charts, good seamanship and a
seaworthy vessel. Always keep a plot going on a chart.
Double check your navigation receiver fixes with compass bearings on
coastal passages.
The
Global Maritime Distress and Safety System (GMDSS) has been fully
implemented. For commercial shipping over
300grt and is now on a fully automated and satellite based
communications and safety system. The
problem is that yachts are now unplugged from this safety system. Already major radio shore stations are closed
for HF/SSB operations. The main elements
of GMDSS are INMARSAT C, Navtex, VHF and SSB/HF Telex and Digital
Selective Calling (DSC), EPIRBS and SARTS.
Under
the GMDSS the world is divided into areas for search and rescue and
these areas are based on the NAVAREA zones. The 121.5/243 MHz and 406
MHz EPIRB units are COSPAS-SARSAT compatible. This
is
a
world-wide satellite assisted SAR system for location of distress
transmissions emitted by EPIRB's. The 406
MHz beacons can have a unique identification code in the distress
message so that precise vessel data can be included. Search &
Rescue Transponders (SART’s)
are devices are designed for use
in search
and rescue. An EPIRB will put potential rescue vessels in the area, but
the transponder will accurately localize your position.
The EPIRB is generally the first GMDSS compatible item purchased
for the yacht, and if the budget allows and you go deep sea then a
406MHz unit is the way to go
NAVTEX
is
controlled
by the various navigation authorities within each of the
16 Navareas who participate in the provision of meteorological and
Maritime Safety Information (MSI) navigational safety information for
transmission. NAVTEX is the broadcasting
of weather and navigational information by teleprinter.
It is an integral part of GMDSS. Broadcast
frequency
for
NAVTEX is 518kHz and uses a dedicated receiver,
permanently tuned to the frequency, and an integral printer is used. In normal use, the unit is left on
permanently, and can be programmed to receive specific messages. Ranges are typically around 250nm. There are some excellent smaller units around
such as those from ICS Electronics, and as a second step towards GMDSS
it is a sensible purchase.
Digital Selective Calling (DSC). DSC is at the heart of GMDSS communications. DSC has a number of important features. It utilises a single VHF channel, specifically
channel 70. A digitally encoded message is
transmitted instead of a voice one. For
many the obtaining of a new compatible VHF is a vexed and expensive one. There are a number of new GMDSS units
available specifically for yachts and smaller vessel.
This makes a good third step in the switchover to GMDSS, so get
either a VHF that can be upgraded later or go for the full unit. Remember licensing requirements are different,
and a new course and certificate is also required.
For
the
Blue Water cruising sailor
the whole question of long range communications within a GMDSS context
is a very difficult one. Whilst Amateur or HAM radio is now
proving its value and worth to the primarily USA based cruisers, and
there are some useful commercial E-mail services on HF now available,
the whole question is still a hard one to address. Iridium is
literally in a satellite "crash and burn" situation, so
any salvation
on that front is seemingly limited, and INMARSAT services are somewhat
expensive for cruisers, although a range of marketing options are
becoming available.
GMDSS
Information from the US Coast Guard:
Over fifteen years ago the International Maritime Organization (IMO), a United Nations agency specializing in safety of shipping and preventing ships from polluting the seas, began looking at ways of improving maritime distress and safety communications. In 1979, a group of experts drafted the International Convention on Maritime Search and Rescue, which called for development of a global search and rescue plan. This group also passed a resolution calling for development by IMO of a Global Maritime Distress and Safety System (GMDSS) to provide the communication support needed to implement the search and rescue plan. This new system, which the world's maritime nations, including the United States, are implementing, is based upon a combination of satellite and terrestrial radio services, and has changed international distress communications from being primarily ship-to-ship based to ship-to-shore (Rescue Coordination Center) based. It spelled the end of Morse code communications for all but a few users, such as Amateur Radio. The GMDSS provides for automatic distress alerting and locating in cases where a radio operator doesn't have time to send an SOS or MAYDAY call, and, for the first time, requires ships to receive broadcasts of maritime safety information which could prevent a distress from happening in the first place. In 1988, IMO amended the Safety of Life at Sea (SOLAS) Convention, requiring ships subject to it fit GMDSS equipment. Such ships were required to carry NAVTEX and satellite EPIRBs by 1 August 1993, and had to fit all other GMDSS equipment by 1 February 1999. US ships were allowed to fit GMDSS in lieu of Morse telegraphy equipment by the Telecommunications Act of 1996.
The GMDSS consists of several systems, some of which are new, but many of which have been in operation for many years. The system will be able to reliably perform the following functions: alerting (including position determination of the unit in distress), search and rescue coordination, locating (homing), maritime safety information broadcasts, general communications, and bridge-to-bridge communications. Specific radio carriage requirements depend upon the ship's area of operation, rather than its tonnage. The system also provides redundant means of distress alerting, and emergency sources of power.
The GMDSS consists of many separate systems which are being implemented in a coordinated and agreed-upon manner. Some of these systems are discussed on the following page.
COSPAS-SARSAT
is an international satellite-based search and rescue system,
established by Canada, France, the U.S.A., and Russia. These four
countries jointly helped develop a 406 MHz satellite emergency
position-indicating radiobeacon (EPIRB), an element of the GMDSS
designed to operate with COSPAS-SARSAT system. These
automatic-activating EPIRBs, now required on SOLAS ships, commercial
fishing vessels, and other ships, are designed to transmit to a rescue
coordination center a vessel identification and an accurate location of
the vessel from anywhere in the world.
NAVTEX
NAVTEX is an international, automated system for instantly distributing maritime navigational warnings, weather forecasts and warnings, search and rescue notices and similar information to ships. A small, low-cost and self-contained "smart" printing radio receiver installed in the pilot house of a ship or boat 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. If it is a new and wanted message, it is printed on a roll of adding-machine size paper; if not, the message is ignored. A new ship coming into the area will receive many previously-broadcast messages for the first time; ships already in the area which had already received the message won't receive it again. No person needs to be present during a broadcast to receive vital information. See Practical Instruction for the Use of a NAVTEX Receiver (Acrobat PDF).
INMARSAT
Satellite systems operated by the Inmarsat, under contract to the International Maritime Satellite Organization (IMSO), are also important elements of the GMDSS. Three types of Inmarsat ship earth station terminals are recognized by the GMDSS: the Inmarsat B, C and F77. The Inmarsat B and F77, an updated version of the 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 centers. The F77 is meant to be be used with the Inmarsat C, since it's data capability does not meet GMDSS requirements. 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.
Inmarsat C equipment is relatively small and lightweight, and costs much less than an Inmarsat B or F77. Inmarsat B and F77 ship earth stations require relatively large gyro-stabilized antennas; the antenna size of the Inmarsat C is much smaller. .
In July 2002 IMSO notified IMO of the decision by Inmarsat to withdraw provision of Inmarsat A services as from 31 December 2007. On that date, Inmarsat A can no longer be used for any purpose. The last type approval by Inmarsat for a new model of maritime Inmarsat A mobile earth station was granted in 1991, since when no new Inmarsat A models have been approved.
Under a cooperative agreement with the National Oceanic and Atmospheric Administration (NOAA), combined meteorological observations and AMVER reports can now be sent to both the USCG AMVER Center, and NOAA, using an Inmarsat C ship earth station, at no charge. There is also no charge to register for this service and to receive the necessary Inmarsat C software. For more information, see the NOAA Shipboard Environmental (data) Acquisition System, or SEAS.
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 center if a distress alert is ever transmitted.
High Frequency
The GMDSS includes HF radiotelephone and radiotelex (narrow-band direct printing) equipment, with calls initiated by digital selective calling. Worldwide broadcasts of maritime safety information are also made on HF narrow-band direct printing channels.
To meet these GMDSS requirements, the Coast Guard has improved high frequency (HF) ship-shore radio safety services from our Communication Stations to the maritime community, as well as narrow-band direct printing broadcasts.
Search and Rescue Radar Transponders (SARTs).
The GMDSS installation on ships include one or more search and rescue radar transponders, devices which are used to locate survival craft or distressed vessels by creating a series of dots on a rescuing ship's 3 cm radar display. The detection range between these devices and ships, dependent upon the height of the ship's radar mast and the height of the SART, is normally about eight nautical miles. Note that a marine radar may not detect a SART even within this distance, if the radar settings are not optimized for SART detection. For more information, see IMO SN/Circ.197, Operation of Marine Radar for SART Detection. (PDF)
Digital Selective Calling
The IMO also introduced digital selective calling (DSC) on VHF, MF and HF maritime radios as part of the GMDSS system. DSC is primarily intended to initiate ship/ship, ship/shore, and shore/ship radiotelephone and MF/HF radiotelex calls. DSC calls can also be made to individual ships or groups of ships. DSC distress alerts, which consist of a preformatted distress message, are used initiate emergency communications with ships and rescue coordination centers. DSC was intended to eliminate the need for persons on a ship's bridge or on shore to continuously guard radio receivers on voice radio channels, including VHF channel 16 (156.8 MHz) and 2182 kHz now used for distress, safety and calling. A listening watch aboard GMDSS-equipped ships on 2182 kHz ended on 1 February 1999. In May 2002, IMO decided to postpone cessation of a listening watch on VHF CH.16 aboard ships. That watchkeeping requirement had been scheduled to end on 1 February 2005.
IMO and ITU both require that the DSC-equipped VHF and MF/HF radios be externally connected to a satellite navigation receiver. That connection will ensure accurate location information is sent to a rescue coordination center if a distress alert is ever transmitted. FCC regulations actually require that ship's position be manually entered into the radio every four hours on ships required to carry GMDSS equipment, while that ship is underway (47 CFR 80.1073).The Coast Guard believes VHF, MF and HF radiotelephone equipment carried on ships should include a DSC capability as a matter of safety. To achieve this, the FCC requires that all new VHF and MF/HF maritime radiotelephones type accepted after June 1999 to have at least a basic DSC capability.
VHF digital selective calling also has other capabilities beyond those required for the GMDSS. The Coast Guard uses this system to track vessels in Prince William Sound, Alaska, Vessel Traffic Service. IMO and the USCG also plan to require ships carry a Universal Shipborne Automatic Identification System, which will be DSC-compatible. Countries having a GMDSS A1 Area should be able to identify and track AIS-equipped vessels in its waters without any additional radio equipment.
A DSC-equipped radio cannot be interrogated and tracked unless that option was included by the manufacturer, and unless the user configures it to allow tracking.
U.S. shore-based radio stations currently exist to support every element of the GMDSS, except for digital selective calling. The United States intends to declare an Sea Area A1 in 2006 and a Sea Area A2 for the contiguous U.S. will be declared once the 2 MHz infrastructure has been upgraded.
Use of GMDSS for Routine TelecommunicationsGMDSS telecommunications equipment should not be reserved for emergency use only. The International Maritime Organization in COMSAR Circ.17 encourages mariners to use that equipment for routine as well as safety telecommunications.
Updated
weekly
and available on a 24-hour per day/ 7-day per week basis, this system
contains characteristics of over 400 000 ship stations as well as the
addresses and contact information of Accounting Authorities (AAICs) and
Notifying Administrations.
http://www.gmdss.com.au/index.html
GMDSS
Information
by Densham and Associates - Australia
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All DSC-equipped radios, and most GPS receivers, have an NMEA 0183 two-wire data interface connector. That NMEA interface allows any model of GPS to be successfully interconnected to any model of radio, regardless of manufacture. Although NMEA has no standard for the type of connector used, many if not most DSC and GPS receiver manufactures use bar wire connections. These wires are simply connected between the radio and the GPS by twisting the wires (some people solder) and tape (some people use waterproof heat shrink tubing). Note also that NMEA 0183 and IEC 61162-1 data interfaces are identical.
The Coast Guard urges, in
the
strongest terms possible, that you take the time to interconnect your
GPS and DSC-equipped radio. Doing so may save your life in a
distress situation!
|
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| 802.11 |
A family of IEEE
(Institute of Electrical and Electronic Engineers, Inc.) standards for
wireless LANs first introduced in 1997. The original 802.11
specification provides 1 or 2 Mbps transmission in the unlicensed
2.4GHz band using either a frequency hopping modulation (FHSS)
technique or direct sequence spread spectrum (DSSS), also known as
CDMA. The 802.11b standard is rated at 11 Mbps in the 2.4GHz band, but
delivers approximately 7 Mbps in practice. The Wireless Ethernet
Compatibility Association (WECA) endorsed the DSSS version of 802.11b
branding it "Wi-Fi" for Wireless Fidelity. Thus, 802.11b and Wi-Fi have
become synonymous. A faster 802.11a standard provides from 6 to 54 Mbps
at 5GHz, but is not backward compatible with 802.11b. A subsequent
802.11g standard provides up to 54 Mbps at 2.4GHz as well as backward
compatibility with the slower 11b. Both 11a and 11g use orthogonal FDM
(OFDM) modulation to achieve the higher rates. An 802.11 system works
in two modes. In "infrastructure mode," wireless devices communicate to
a wired LAN via access points. Each access point and its wireless
devices are known as a Basic Service Set (BSS). An Extended Service Set
(ESS) is two or more BSSs in the same subnet. In "ad hoc mode," also
known as "peer-to-peer mode," wireless devices can communicate with
each other directly and do not use an access point. This is an
Independent BSS (IBSS). Maximum Frequency Modulation Standard Speed
Range Technique 802.11a 54 Mbps 5GHz OFDM 802.11b 11 Mbps 2.4GHz DSSS
802.11g 54 Mbps 2.4GHz OFDM/DSSS |
It all used to be so simple. There was a VHF radio for short range communications and an SSB radio for long range communications. Now there are decisions to be made about DSC and GMDSS, VHF versus cellular, and even flowcharts to follow when responding to a distress call - if you're meant to respond at all.
Much of the confusion stems from a decision in 1979 by the International Maritime Organization to improve upon the marine communications available for safety and distress alerting as well as search and rescue operations. This led to the creation of the Global Maritime Distress and Safety System or GMDSS. One of the first things they did when creating this system, was to separate the world into four distinct and non-overlapping regions called Sea Areas. These Sea Areas correspond loosely to coastal, near-coastal, high seas and polar regions (see Table 1).
Table 1: GMDSS Sea Areas
| Sea Area | Approximate Range | Description |
| A1 | coastal up to 30 miles | within range of coast VHF stations |
| A2 | from A1 limit out to about 150 miles | within range of coast MF stations |
| A3 | 70 degrees N to 70 degrees S, outside of A1 and A2 | within range of Inmarsat satellites |
| A4 | all other areas | polar regions not covered by Inmarsat |
Picture a shipboard radar display, with overlaid electronic chart data, that includes a mark for every significant ship within radio range, each as desired with a velocity vector (indicating speed and heading). Each ship "mark" could reflect the actual size of the ship, with position to GPS or differential GPS accuracy. By "clicking" on a ship mark, you could learn the ship name, course and speed, classification, call sign, registration number, MMSI, and other information. Maneuvering information, closest point of approach (CPA), time to closest point of approach (TCPA) and other navigation information, more accurate and more timely than information available from an automatic radar plotting aid, could also be available. Display information previously available only to modern Vessel Traffic Service operations centers could now be available to every AIS-equipped ship.
With this information, you could call any ship over VHF radiotelephone by name, rather than by "ship off my port bow" or some other imprecise means. Or you could dial it up directly using GMDSS equipment. Or you could send to the ship, or receive from it, short safety-related email messages.
The AIS is a shipboard broadcast system that acts like a
transponder, operating in the VHF maritime band, that is capable of
handling well over 4,500 reports per minute and updates as often as
every two seconds. It uses Self-Organizing Time Division
Multiple Access (SOTDMA) technology to meet this high broadcast rate
and ensure reliable ship-to-ship operation.
