Semaphore.
Semaphore is a means of signalling employing two hand held flags held in various positions relative to the communicator’s body. The flags used are the same, ie flag OSCAR (flag diagonally split by the colours red and yellow. This form of communicating is virtually obsolete today but it may still be employed in various parts of the world.
Semaphore.
Flashing light.
Flashing light was used quite extensively for ship to ship communications not too long ago and it remains a very good standby especially in a wartime situation when you do not wish the enemy to intercept your radio communications.
In order to use flashing light as a means of communication a special code had to be developed and used internationally. This code is known as the Morse code. By altering the duration of the flashes to short and long flashes and combining them in various groups it was possible to use the light for passing messages. The code and its designations are contained in the Morse Code/Phonetic Alphabet table. To assist the communicator in cutting down the amount of time spent in using the light, certain abbreviations were developed. These are also included in the Signalling by Flashing Light table. Basically they are used in a similar fashion to flags, ie they can be used to spell out a message in plain language or they can use a combination of letters and numerals in a special code.
Basically the procedure would be as follows:
Ship A calls ship B using their international call signs (a combination of letters and/or figures used to identify a particular ship or shore authority) or the ships’ names. The answering ship would acknowledge the call. The sending ship would then spell out the message letter by letter until a word has been completed. The sender would then wait until the other ship acknowledges that it has received the word correctly. It does this by sending one long flash after each word is sent. If he didn’t get the complete word, he does not send the long flash. The sending ship will resend the particular word until it gets a long flash in return. If the sender, on completion of his message, wants a reply, he/she sends the morse equivalent of the letter “K”. If it does not want a reply it sends the morse equivalent of the letters “AR” transmitted as a single entity.
The lamps/projectors used for flashing light varies from small hand-held projectors to large, mounted projectors. In this form the signalling is directional, ie the projector is aimed like a torch at the vessel with which they wish to communicate. If it is desired to talk to more than one vessel, use can be made of the masthead-mounted omni-directional signal light. It would then be visible 360° and any vessel within range will be able to read the light. Persons using this form of communication will need to master the skill necessary to read and transmit the light flashes. This takes much time and practice.
20 inch signalling projector.
Portable Aldis signalling projector.
Advantages of using flashing light:
- Like flags it is silent.
- It can be read during the day and at night.
- Compared to flags it is fairly fast.
- Again compared to flags it can handle a larger volume of traffic.
Disadvantages. The downside of flashing light are the following:
- Its range is limited to line of sight.
- It cannot be seen in restricted visibility (fog).
- It is not private unless the traffic is encrypted. Anyone within the range of the light can
read the messages. - It requires the user to possess certain skills to operate the light and read it.
Signalling by flashlight.