This is a very fast method of communication when transmitted by an experienced operator. It may be carried out by Aldis lamp, direct to the receiving station, or by an all round lamp, either method being limited in range to the visual distance between transmitting and receiving stations. This method of communication is used between ship to shore as well as ship to ship. Normal speed of transmission is four to six words per minute.
The Aldis lamp should be kept readily available for emergency use if required. It is normally provided with sun shades, usually red and green, to allow operation during the hours of daylight.
Morse Code by Wireless Telegraphy (W/T)
With the full implementation of GMDSS from February 1999, Radio Officers and the use of W/T are virtually no longer used within the maritime communications field. Full world satellite coverage is now possible and all vessels over 300 GT are equipped to operate under the GMDSS regulations. It is a requirement of GMDSS compliance that a vessel must carry at least two qualified certificated personnel capable of operating the communication equipment.
NB. In the event of the vessel being requisitioned for a Search and Rescue operation, a designated communications operator must be identified within the bridge team.
Morse Code by Flag
This is a very slow and tiring method of communication. Transmission should be carried out slowly unless a person is very experienced in this style of signalling. Limited in range, it has the advantage that an injured party with only one arm available can use it.
This method employs two hand flags, which are positioned to indicate letters of the alphabet. It is limited in range to the visual distance between the transmitting and receiving stations. A good operator can transmit fifteen to eighteen words per minute. However, semaphore has been made obsolete in both the Royal Navy and the British mercantile marine, and it is no longer a requirement for deck officers to have detailed knowledge of it in order to qualify for a certificate of competency.