Feature 5 | COMMUNICATIONS SYSTEMS
whether links are shared or dedicated and how many users there are concurrently). High-precision stabilised platforms
and servo tracking systems are needed to align antennas to a tolerance of 0.1 to 0.2 degrees compared with 1-2 degrees needed for an Inmarsat system. These, along with advanced radio frequency (RF) modules, account for a substantial proportion of a VSAT’s weight and cost. VSAT appeals to superyacht owners and
professional users ranging from the oil and gas sector to cruise shipping. The system exploits transponders on multiple existing geostationary satellites operating in the C-band or Ku band (Amerisat, USAT etc). As coverage is not global, service providers tend to focus on particular regions such as the Mediterranean or the Caribbean that are within the footprints of particular satellites. Service is normally charged on payment of a quarterly subscription plus per-byte charge. Thrane & Thrane has recently entered the VSAT market with its Sailor 900 VSAT system. More accessible at the small ship and
boat level is mini-VSAT. Using antennas that are much smaller and lighter than for standard VSAT, mini-VSAT is more affordable and easier to install and maintain. As an example, the TracPhone V7 from KVH Industries featured by CA Clase at the recent Southampton Boat Show provides up to 512kbit/s for
Thrane & Thrane VSAT equipment.
ship-to-shore transmissions and 2MB/s for shore-to-ship downloads. KVH says the system is particularly reliable and supports a range of Internet-based services including several crystal-clear voice channels, video conferencing, instant messaging, corporate network access, multimedia entertainment and large-volume data transfer. The terminal measures 60cm diameter and weighs 27kg. The company claims that mini-VSAT is
suitable for craft down to about 50ft loa and it offers flexible rate plans to meet different owner needs. KVH also offers FleetBroadband TracPhones in FB250 and FB500 sizes and the TracVision M-series for satellite TV reception. Another VSAT provider, focusing strongly on stabilised antennas for DVB-S (digital video broadcasting via satellite), is Sea-Tel with C- and Ku-band services that include voice, fax and HDTV.
Mobiles on board A recent and far-reaching change has been the opening to the masses of maritime communications, enabling those at sea to use mobile devices on an individual basis. Until recently, passenger and crew calling – if available at all – was cumbersome, utilising facilities also used for ships’ business. Seafarers on some fishing boats, workboats and other craft
operating close inshore have for some time been able to use their own mobile phones, but more than a few miles offshore these lose contact with terrestrial networks and are rendered useless. This has prompted some professional boat users, along with leisure boaters, to invest in satellite phones. Most of these utilise low earth orbiting (LEO) satellite constellations, principally Iridium, Globalstar and Thuraya. Iridium claims to be the only provider
offering full global coverage, including the polar regions, thanks to its constellation of 66 satellites that circle the earth obliquely. Although this poses the complication that data has to be sent via a number of moving satellites rather than one that is fixed over a particular earth location, the system has proved robust and there are economies due to the shorter signal paths to satellites operating in low orbits. Moreover the latency (delay) noticeable with GEO satellites due to their high (36,000km) orbits is negligible with LEO-based services. The popular Iridium 9505A satphone
provides global voice telephony, text and data services at up to 2.4kbit/s via a handset measuring just 158mm long by 62mm wide by 59mm deep and weighing 375g. The water and shock-resistant phone provides a continuous talk time between recharges of up to 3.6hours, e-mail text using MS Outlook software and the usual ring and/ or vibrate, memory storage and last ten numbers dialled facilities. The phone has its own allocated telephone number and pre or post payment options are available. Iridium had also developed for the maritime market its OpenPort system providing up to three phone lines simultaneously, along with always-on data at up to 128kbit/s, on an all-IP backbone. Globalstar similarly aims to offer a
reliable, low-cost voice and low-rate data service via satphones. Its Telit 550 handheld phone is dual-mode, operating in satcom mode for communication when at sea or GSM mode when within direct reach of terrestrial networks. It passes secure Code Division Multiple Access (CDMA) standard signals via 40 LEO satellites and claims to be effective over 80% of the earth’s surface, excluding polar and certain mid-ocean regions.
60 Ship & Boat International November/December 2008
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72