A shipboard radio station includes all the transmitting and receiving equipment installed aboard a ship for communications afloat. Depending on the size, purpose, or destination of a ship, its radio station must meet certain requirements established by law or treaty. For example, large passenger or cargo ships that travel on the open sea are required by the Communications Act and by international agreements to be equipped with a radio station for long distance radio communications. Small passenger ships that travel along the coast may only need to communicate at shorter range with coast stations. These are examples of "compulsory ships" because they are required or compelled by treaty or statute to be equipped with specified telecommunications equipment.
Smaller ships used for recreation (e.g., sailing, diving, sport fishing, fishing, water skiing) are not required to have radio stations installed but they may be so equipped by choice. These ships are known as "voluntary ships" because they are not required by treaty or statute to carry a radio but voluntarily fit some of the same equipment used by compulsory ships.
Ship stations may communicate with other ship stations or coast stations primarily for safety, and secondarily for navigation and operational efficiency. The FCC regulates marine communications in cooperation with the U.S. Coast Guard, which monitors marine distress frequencies continuously to protect life and property. All users of marine radio, whether voluntary or compulsory, are responsible for observing both FCC and Coast Guard requirements.