Radio Room Clock: What It Is and How It Works

The radio room clock is a special shipboard clock used in the radio rooms of ships. Its purpose is to indicate periods of radio silence, during which it is forbidden to transmit or receive radio signals.

Why is radio silence necessary?

Radio silence is necessary to avoid interference with the transmissions of other ships or radio stations. These interferences can cause communication, navigation, or safety problems.

How does the radio room clock work?

The dial of the radio room clock is divided into two colored sectors: red for telegraph silence and green (or a different shade of red) for radio silence..

  • Telegraph silence lasts three minutes and starts 15 and 45 minutes after each hour.
  • Radio silence lasts three minutes and starts 0 and 30 minutes after each hour.

A curiosity

An ancient seafaring legend tells that, in the past, sailors used another technique to indicate periods of radio silence. This technique consisted of ringing a bell three times, at three-minute intervals.


The radio room clock is an important tool to ensure the safety and efficiency of radio communications at sea.

Other details

In addition to its main function of indicating periods of radio silence, the radio room clock can also be used to indicate the current time, date, and position of the ship.

Some radio room clocks also have additional features, such as a chronograph or a timer.

The radio room clock is an iconic object in maritime culture. It is a symbol of tradition and innovation, and it represents the importance of radio communications for navigation.

Additional details

The radio room clock is typically located in the radio room of a ship. It is used by the ship’s radio operators to ensure that they do not transmit or receive radio signals during periods of radio silence.

The radio room clock is a relatively simple device, but it is an essential part of maritime safety. It helps to ensure that ships can communicate effectively with each other and with shore stations, and it helps to prevent accidents and collisions at sea.

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