Class guidelines for shipboard wireless LAN systems
The growing possibilities for using electronic communication onboard ships have received a boost from ClassNK, which has produced some timely guidelines for shipboard wireless LAN (local area network) systems.
The society says that its Guidelines on shipboard wireless LAN systems can help in two ways. First, to serve as a reference when such systems are being fitted on board. Second, as a useful foundation for future work in this area, because guidelines for these systems and their shipboard applications will eventually become standardised.
Shipboard LAN began to emerge in the 1980s as ship-to-shore communication increased, and it was recognised that voyage and machinery data needed to be integrated into a ship’s systems. The growth of satellite technology as well as the kind of sophisticated kit that appeared on research and survey ships increased the scope of what could be done with shipboard LAN.
Typically, these systems tended to be wired versions. This began to change as wireless technology grew, and systems available ashore inevitably migrated to ships.
The basic design for a wireless LAN (WLAN) system comprises an access point, a network switch, a wireless terminal (which could be a personal computer or ‘voice over internet protocol’ telephone), a control server and LAN cable. Access points installed at various locations on the ship are wired with LAN cables using network switches as the pivot points. The control server may be found in the wheelhouse, the cargo or engine control room, or another suitable location.
Standards governing WLAN follow those established by the Institute of Electrical & Electronic Engineers’ LAN/MAN committee, also known as the IEEE 802 committee, which created and maintains the IEEE 802.11 set of standards for WLAN computer communication in the 2.4, 3.6 and 5 GHz frequency bands. The 802.11 family includes over-the-air modulation techniques that use the same basic protocol. Each country establishes its own rules based on these standards: for example, protocol 802.11n is a new multi-streaming modulation technique used in Japan.
A certification system for technical regulations based on the Radio Law of Japan requires WLAN equipment used onboard ships under the Japanese flag to comply with these regulations. Those that do carry the relevant conformity mark.
Likewise, on ships likely to enter EU waters, all equipment, at least in principle, should carry the CE (conformité européenne) mark. In addition, it is a good idea to have access points on the bridge cleared by the electromagnetic compatibility (EMC) test in the International Electrotechnical Commission’s latest (fourth edition) standards (IEC60945 Ed 4).
There are a number of permitted frequencies acceptable in different countries. “Careful attention must be paid to the latest conditions of the restriction in any countries of particular concern,” ClassNK notes, adding that wireless LAN equipment should not be used in a port where its use is restricted.
Equipment should work on 100V to 220V AC power supplies. It should remain functional if experiencing a 6% rise in power, or a 10% drop. In the event of a blackout, the equipment should be capable of immediate operation when power is restored.
Equipment should be installed in areas which are adequately ventilated but if this proves to be impossible and it has to be positioned, for example, where combustible gas is likely to accumulate, then the equipment should be of a type approved as explosion-proof.
While wireless LAN has a lot of advantages, one of its drawbacks compared with a wired system is security. Hence, in the guidelines, ClassNK states that wired equivalent privacy (WEP) is not recommended since it is susceptible to decoding in a short period of time. Instead, to avoid unauthorised connection, the society recommends wi-fi protected access (WPA-PSK), which is a method of encrypting wireless transmission data.
Another drawback is the stability of communications which can depend on the environment in which the system is located. On a ship, for example, voyage and surveillance data can be transmitted via WLAN. However, measures need to be taken to ensure that factors causing noise and improper operation are not transmitted from any shipboard equipment providing essential or non-essential services and connected to the WLAN system. The same is true the other way round, and care should be taken to make sure that faults in the WLAN system do not affect other equipment.
To avoid compromising vital control capabilities, it is possible to install interface equipment to insulate the space between the navigation equipment or monitoring system and the WLAN system.
Of course, a wireless system has less need of expensive cable laying. A characteristic of the wireless system’s basic design is the access point: if this has a repeater function for relaying data between wireless terminals, it is possible to connect access points without cable, thereby reducing costs. The lack of wiring in a wireless system also highlights the system’s flexibility.
Once set up, the WLAN system will need to be tested. If it complies with the guidelines which limit its application to non-vital services, the presence of a surveyor is not required at confirmation tests of its operation. But where WLAN equipment has not cleared the IEC60945 Ed 4 EMC test, it must be confirmed during sea trials that it does not affect navigational equipment and vice versa.
An example of the use of WLAN can be illustrated by a crew safety management system developed jointly by Mitsubishi Heavy Industries and the Furuno Electric Company, and announced at the Sea Japan exhibition in 2008. The crew safety system features a wireless IP (internet protocol) telephone set-up that enables talking in all areas of the ship when each crew member carries a wireless IP telephone. It combines this with a WLAN position data system that tracks the position of the wireless IP telephones by detecting the connection data between the access point and the wireless telephone.
The system offers the same functions commonly available in mobile phones – voice and instant messaging, and image sending. But it also has integrated control of crew members’ position data onboard, enabling an early and effective response in the event of a fire, for example. And if this data is then recorded and stored, it would make a useful contribution to post-accident analyses.
As well as offering guidance on the installation and maintenance of WLAN systems onboard ship, the ClassNK guidelines list the main technical regulations and provide a summary of the main terms in use.
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