Source: americanboating.org

By Captain Bob Figular, reprinted with permission from Mariner’s Learning System

Today most marine communications are accomplished by using voice radio transmissions. These radio systems are similar to having a conversation on the telephone, but with significant differences that boat operators must understand. Typically, voice radio communications are “simplex,” or one direction at a time – when one person is talking, the second person may not speak. This differs from face-to-face and telephone conversations we are accustomed to where voices may overlap. Simplex communication is the primary reason for many of the procedural regulations for speaking on a marine radio. As a boat operator, using a marine radiophone will be an occasional responsibility. It is important to understand and be comfortable with the proper operation of your vessels marine radio. In this article we will take a look at some standard procedures and protocol as they relate to the proper operation of your boats marine radiophone.

First we must realize that there are several different types of marine radios. On boats, they are frequently MF/HF and VHF-FM, and usually, are identified by the radio’s mode of transmission. Understanding the basic differences of the types of radios and their use will assist you in determining the best solution to your personal/professional boating needs:

• VHF-FM (156‑162 MHz) is used for local, short-range marine communications. Frequencies in this band operate on the line-of-sight (LOS) principle. Effective communications range depends mainly on the height of antennas of both the receiving and transmitting stations, and somewhat on the power output of the transmitting station. VHF equipment is called “line-of-sight radio” because its radio waves travel in nearly a straight line, meaning, if one antenna can “see” another antenna, communications between the two is possible. Occasionally, atmospheric conditions allow VHF signals to bounce or bend in their line of travel, increasing the transmission’s range farther than normal.
• Boats use the MF band typically to communicate when out of VHF radio range. The MF band uses low frequencies, so the ground wave travels along the surface of the earth, permitting communications at distances up to 200 miles during daylight hours. The low frequency also makes communications at much greater distances at night easier. MF and HF radios of any modulation type always have greater range than VHF. The operating range for MF and HF radios can shift as conditions change, and the conditions that affect the operating range will typically vary from hour to hour. As a consequence, communications between two vessels can be lost due to a number of factors, including changing weather.