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. 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. A sailor planning to set out without a radio, however, is likely to receive shocked and skeptical looks from others.
Today there are two basic kinds of radios found aboard ocean-going vessels.
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 has a much greater range than VHF because it does not require a line of sight between stations. 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. Satellite communication Satellite communication is a relatively new alternative for long-distance communication. Instead of transmitting an analog signal directly from the vessel to a shore station, a digital signal is transmitted upward to a satellite.