Essential equipment for marine communications

A vast array of marine communications equipment is carried on modern ships. Leaving aside personal devices such as mobile phones and computers able to connect to 3G and 4G data networks or wi-fi hotspots, the lowest level of marine communications is the VHF radio.

VHF operates on a range of frequencies with each frequency given a channel number. There are more than 80 channels but not all are used for marine purposes. While many channels are allocated by international agreement for specific purposes, others are reserved for specific communication purposes by national maritime authorities or VTS systems.

The following VHF marine frequencies have been set aside by the ITU for particular purposes. These frequencies are internationally accepted by most nations and will be found on all VHF Marine Radios regardless of where or by whom they are manufactured.

  • Channel 16 (156.800 MHz) – The international distress, safety and calling frequency.
  • Channel 70 (156.525 MHz) – Digital Selective Calling frequency.
  • Channel 13 (156.650 MHz) – Bridge to Bridge navigation frequency.
  • Channel 06 (156.300 MHz), Channel 10 (156.500 MHz), Channel 67(156.375 MHz), and
  • Channel 73 (156.675 MHz) have been set aside for coordinated search and rescue operations.

Many countries have assigned closely related safety marine communications traffic to these frequencies as well as their primary SAR usage. Channels can be either simplex or duplex. Simplex is where both transmitter and receiver are operating on a single (or the same) frequency, for example VHF CH12 and VHF CH 16. On simplex channels it is not possible to transmit and receive simultaneously.


Simplex channels are mainly used for distress, urgency, safety and routine calling purposes, port, pilotage, harbour and inter-ship operations. Conversations on simplex channels can be heard by all receivers operating on the same channel.

Duplex channels are normally only used for communication between vessels and coast radio stations and for port operations and ship movement. With duplex channels transmissions can only be heard by the coast radio station. However, all ship stations listening to the same channel can hear the coast radio station transmission.

VHF radios can be fixed or portable. The fixed equipment is housed on the bridge or radio room and will likely be part of the ship’s GMDSS equipment. It will be used for bridge to bridge marine communications and conversations with VTS etc.

Portable VHF radios are used on ships for routine on board marine communications such as when mooring and unmooring or during cargo handling when conversations may take place between the ship and stevedores ashore. Some portable VHF sets will have GPS and DSC capability meaning they can be used for both routine and GMDSS purposes.

The IMO performance standard requires that portable VHF equipment intended to be used in lifeboats and liferafts should:

  • provide operation on VHF channel 16 (the radiotelephone distress and calling channel) and one other channel
  • be capable of operation by unskilled personnel
  • be capable of operation by personnel wearing gloves
  • be capable of single handed operation, except for channel changing
  • withstand drops on to a hard surface from a height of 1m
  • be watertight to a depth of 1m for at least 5 minutes, and maintain watertightness when subjected to a thermal shock of 45°C
  • not be unduly effected by seawater or oil
  • have no sharp projections which could damage survival craft
  • be of small size and weight
  • be capable of operating in the ambient noise level likely to be encountered on board survival craft
  • have provisions for attachment to the clothing of the user
  • be either a highly visible yellow/orange colour or marked with a surrounding yellow/orange marking strip
  • be resistant to deterioration by prolonged exposure to sunlight.`

Approved VHF sets of fixed and portable and both GMDSS and non-GMDSS types are freely available at almost every port from ship chandlers and specialist equipment providers. Prices vary but the normal outlay is between $100 and $200 for a handheld VHF and fixed sets costing around double that.

GMDSS Stations

Depending on the sea areas (A1-A4) a ship operates in, the GMDSS requirements will dictate what communications systems are carried. It is possible to assemble a GMDSS compliant set-up from individual components but most ships are fitted with an integrated station supplied by one of the many specialist communications and navigation equipment providers.

An integrated station has several benefits over a custom assembled setup. Firstly, compatibility and connectivity is guaranteed and secondly only a single power supply connection is needed. As most integrated systems are supplied by major equipment suppliers, the issue of spare parts and repairs is likely to be much less of a problem with access to an established network of agents and repair centres.

Even with an integrated station there are some peripheral items that are installed elsewhere, the bridge fixed VHF being a good example. The systems are mostly quite compact and with the screens only needed to display text messages, there is no need for the large displays used elsewhere on the bridge for ECDIS and radar use.

As mentioned earlier, vessels are obliged to carry trained GMDSS operators who must supervise the use of the communications but the automated emergency DSC aspect of the equipment means that in a distress situation, all necessary information can be sent automatically at the touch of a single button by any crew member.

Marine communications satellite systems

Satellite systems comprise two main components, the antenna which is installed above the bridge and the electronics and displays below. With most L-Band systems, the cost of the system and antenna will fall to the ship operator and the equipment will be owned outright.

When opting for VSAT systems, there is a choice with many shipowners preferring to lease the equipment rather than purchase it themselves. Aside from the lower capital outlay, a lease contract will ensure that advances in technology do not render expensive equipment obsolete as the lessor will usually provide upgrades as necessary.

The under deck components of a satellite system are normally nothing other than a less than imposing box of electronics to which multiple components can be attached. If the system has been installed solely for GMDSS purposes, the only connected devices will be the GMDSS station and any remote displays.

Where the satellite system has been installed for reasons other than GMDSS, the attached devices can be many and various. In many ships the satellite communication unit will be connected to a local area network (LAN) to which will also be connected several PCs, communication devices such as telephones, faxes and possible wireless hubs allowing use of mobile phones, PDAs and tablets. Updating of electronic navigation charts is already common on many ships and as the rollout of mandatory ECDIS accelerates it will become even more so.

Another use that is growing is the monitoring of engines and other equipment on board. Sensors on engines recording temperature, pressure and multiple other parameters using a proprietary control unit can have the data they recorded compiled and sent via the satellite to the machinery supplier for constant diagnostics and to satisfy computer-based maintenance programmes.

Remote monitoring and reporting need not be confined to machinery, it is possible to link an output from a ship’s VDR to the communication system and so supply the shore office with information for incident investigation or even real-time monitoring in emergencies. ((link: /guides/remote-assistance-condition-monitoring-insight-report text: You can read more about remote monitoring in this guide)).

On certain research and seismic vessels, the data from instruments can also be compiled and despatched automatically. Despite satellite equipment having now been installed on ships for around four decades, it has to be said that the opportunities and benefits that it offers are only just beginning to be explored. However, with the world fleet growing rapidly in numbers and data usage expanding even faster, the limits of even the increased bandwidth allowed by expansion of VSAT into the Ku and Ka bands could be reached in the not too distant future.

Some industry observers believe that within less than a decade, satellite usage will have increased by a factor of five even without new uses for data transmission becoming available.

Marine Communications: Satellite antennae

Besides, the highly compact cylindrical Iridium antenna, the smallest and least powerful satellite antenna for use on board vessels is the usually conical shaped antenna of the Inmarsat C system. Both are omnidirectional and therefore require no moving parts inside the protective cover. The low power of the Inmarsat C antenna is one of the reasons why the system has to operate on a store and forward basis.

The next step up to Inmarsat Fleet requires a dish antenna that can move on its horizontal and vertical axes to stay aligned with the satellite. Inmarsat Fleet has three sizes of antenna with diameters of 33cm, 55cm and 77cm the particular size corresponding to the system installed. These antennae like all other marine versions are protected by a radome that can either be dome shaped or spherical.

VSAT antennae are more sophisticated still and also are generally much larger than the Inmarsat Fleet versions. They are 3-axis stabilised systems and the dish which can be 3m or more in diameters (although the trend is to smaller 1m size dishes) can move rapidly in any direction to maintain connectivity with the satellite. Most antennae are designed for use with a single band only but as ships are beginning to subscribe to more than one service and more antennae are needed, some manufacturers are looking to combine bands in a single hybrid antenna. As far as hybrid antennas are concerned, there are several major manufacturers which have developed and will soon be marketing antennas that are capable of instantly switching between Ku-band and Ka-band networks.

Marine communications cost management

As ship operators began to get a taste for more communication options, some ships were fitted with a variety of different systems. There might be the standard GMDSS set up, an Iridium phone or data terminal and even possible a broadband or VSAT system as well. Spurred by fierce competition in the sector, service providers had, in the 2000s, begun to offer a number of different tariffs and special offers to attract extra traffic.

These included ‘super quiet time’ reduced rates for ships sending data during periods of the day when traffic was normally low (this would of course vary by region as it was time based) and special days around public holidays when crew calling costs were discounted.

As the rates varied between different networks, determining the least expensive options became rather complicated for the ships with multiple options. At the same time, a number of third party specialists had begun developing devices that could compress data transmissions beyond what was possible using the equipment provided by service providers.

The way was clearly open for innovative companies to develop systems for controlling and managing the situation and these came to be known as ‘middleware’. The equipment sits between the ship’s LAN and the various communication systems with a second identical device located in the shore office.

At scheduled times or whenever a user wishes to transfer data, the devices create a link between the vessel network and the network in the shipowner’s office. The link and the transfer are optimised by compressing the data and choosing the best carrier available.

The choice made is based on user-programmed information on cost structures of the different services and calculations made by the middleware on the time or data size needed for transmission.

Such systems determine the most cost-effective method of transmitting data and can switch between communication systems as appropriate once initial data has been input.

Within a very short time, the service providers themselves began offering similar devices having either developed their own product or by way of acquiring one of the third party manufacturers.

Avoiding obsolescence

One of the claimed advantages of VSAT is that with leased equipment, any technological advances will be made available by service providers upgrading equipment. However, as demand grows some service providers may offer outdated equipment at reduced rates and some shipowners may be keen to avoid ongoing lease costs by negotiating to buy rather than lease equipment.

This may be a good strategy but there is also the chance that as technology advances are adopted, some of the older equipment will either become obsolete or unable to take advantage of new opportunities. For example, anyone that has purchased a Ku-band antenna outright will not be able to make use of the switchable services and redundancy offered by them.

Another factor that needs to be considered by shipowners is the terms of leasing contracts that may be offered. These will be very different from the service contracts offered for older L-band connectivity and should be scrutinised before committing in order to avoid unpleasant surprises further down the line.