1. 2 Technical Information From: http://www.Goals.Com/ClassRm/SailSci/seacom.Htm: Communication at Sea

Vessels on long voyages are often away from land for weeks or months at a time. Even on short voyages, a sailor on a boat is isolated from the land, and it is often difficult to know what is happening only a short distance away. Unless one is close enough to simply yell to people on shore or aboard other vessels, questions must often go unanswered until one returns home. It was natural, then, that early mariners would embrace technologies that allowed them to communicate across distances.

Written messages

One of the oldest methods of remote communication still exists today. One writes a message on a piece of paper and has it delivered to the recipient. For the sailor at sea, this meant receiving letters and important messages at ports where the vessel stopped or from friendly vessels encountered along the way. In some cases, it could take months or even years for a message to reach the addressee.

An even slower and less reliable way to deliver a written note was to seal it inside an empty bottle and throw it overboard, letting wind and current carry it where they would. With time and luck, some person might actually find and read the note. Flags, semaphores, and other systems

For centuries written correspondence remained the most reliable way to get messages across long distances. However, there were much faster ways for vessels to send simple messages while within sight of the shore or other vessels. Through the use of signal flags and semaphore , a message could be sent to anyone who could see it and understand it. Since these messages were visible to everyone nearby, elaborate codes were developed to identify the sender and recipient and to hide the meaning of the message. When Samuel F. B. Morse developed one of the first practical telegraph systems in 1837, he also designed a code for it in which different combinations of dots and dashes represented letters of the alphabet. Although the telegraph, which required a continuous wire linking the sender and receiver, was useless to mariners, Morse Code was very useful: The heliograph was a bright lamp with a shutter that could be opened and closed to produce a sequence of long and short flashes corresponding to Morse's dots and dashes.

Radio

While early sailors relied only upon written messages, signal flags, semaphores, and a few other signaling techniques to communicate, the twentieth century brought major change to communication. In 1901 an Italian inventor named Marchese Guglielmo Marconi transmitted a radio signal across the Atlantic Ocean, and by 1910 the United States had passed a law requiring its passenger ships to have radio equipment on board. Radio made it possible, for the first time, for a vessel out of sight of land or other vessels to keep in touch with the rest of the world. Radio did not immediately eliminate the need for more traditional signaling systems, however, and many of them, including semaphore and heliograph, were in active use through World War II. Even today, signal flags are carried aboard most large vessels and many smaller ones. Still, radio had a profound impact on communication throughout the world, and particularly on the way sailors communicate. Today, it would be understandable if a lone sailor went to sea without a complete set of signal flags, without any knowledge of Morse Code beyond the familiar pattern for SOS (... - - - ...), and without any whistles, horns, drums, bells, or signaling canon. A sailor planning to set out without a radio, however, is likely to receive shocked and skeptical looks from others.

VHF

Today there are two basic kinds of radios found aboard ocean-going vessels. Marine VHF (very high frequency) radios require an uninterrupted line of sight between antennas. This limits their range, and they are usually used to communicate over distances of less than about [x] nautical miles. Most marine radio traffic occurs over VHF radio, since skippers are naturally most concerned about vessels, port facilities, and hazards in their immediate vicinity.

SSB

To communicate over very large distances, especially while a vessel is at sea, many pleasure craft and virtually all commercial and military vessels are equipped with Marine SSB (single side-band) radio. SSB has a much greater range than VHF because it does not require a line of sight between stations. Its signal "bounces" in the earth's atmosphere, enabling it to reach around the planet's curved surface for thousands of miles. Transmitting on SSB requires a great deal of electricity compared to VHF, however, since its signal must be strong enough to travel over great distances through a lot of atmosphere. Northwest Spirit is equipped with both Marine VHF and Marine SSB.

Satellite communication

Satellite communication is a relatively new alternative for long-distance communication. It features many advantages over conventional point-to-point radio. Instead of transmitting an analog signal directly from the vessel to a shore station, a digital signal is transmitted upward to a satellite. The satellite then relays the signal to another satellite or to a receiver elsewhere on the surface of the earth.

Satellite communication is private. When you use conventional SSB or VHF, everybody with a receiver in range can monitor your conversation. Signals transmitted for satellite communication, however, are highly directional, making them much more difficult for the casual eavesdropper to pick up. In the case of digital signals, data can be encrypted, making it extremely secure against even a determined spy. Satellite communication allows direct access to the global communication infrastructure (telephone and computer networks). SSB or VHF, on the other hand, both require an intermediary--such as a ship-to-shore operator--to make the appropriate connections ashore.

Satellite communication is not greatly affected by atmospheric or meteorological conditions. The signal does not have to bounce since it only needs to reach an overhead satellite, which is always within line-of-sight. Because the signal is being transmitted primarily upward, it passes through a relatively thin layer of the Earth’s atmosphere. SSB and VHF transmissions, however, must push their way through a great quantity of distortion-producing atmosphere as they travel across the surface of the Earth.

Geosynchronous satellites

Most communications satellites are in geosynchronous, or geostationary, orbits. This means that each satellite is at an altitude (22,300 miles or so) such that its speed around the earth matches the earth’s rotation. Both the satellite and the surface of the Earth are rotating around the Earth’s axis, but since they are rotating at the same rate, the satellite appears to stay in one place over the Equator. This simplifies signal transmission since once an antenna on the ground is directed toward the satellite, it does not have to be readjusted. The dish antennas used to receive satellite television are directed toward geosynchronous satellites. A vessel as sea, however, does not stay in one place. Even if it did, though, it would tend to provide an insufficiently stable surface for precise antenna alignment.