International Code of Signals — Chapters I-V

1. Overview

Source: INTERNATIONAL MARITIME ORGANIZATION. International Code of Signals. London: IMO, 2005. Este capítulo cobre os Chapters I a V da obra (Explanations and general remarks; Definitions; Methods of signalling; General instructions; Flag signalling) — o Chapter VI (Flashing light signalling), que aparece entre os Chapters V e VII na obra, fica fora do recorte do edital.

Syllabus: Anexo 2-B (bibliografia) — International Code of Signals · Anexo 2-A, item VI Comunicações: VI.3.2 Explicação e observações gerais para emprego do CIS; VI.3.3 Definições; VI.3.4 Métodos de sinalização; VI.3.5 Instruções gerais.

The International Code of Signals exists for one purpose: to give ships, aircraft and shore stations a way to exchange messages about the safety of navigation and of persons when a language difficulty gets in the way. Where no such difficulty exists, plain-language radiotelephony or radiotelegraphy already does the job — the Code is the fallback that still works when the two sides do not share a language.

This chapter covers the five opening chapters of the Code, in the order the book presents them: Chapter I explains what a signal is built from and how to read it; Chapter II defines the vocabulary used throughout the rest of the book; Chapter III lists the methods by which a signal may be transmitted; Chapter IV sets the instructions common to every method — who signals to whom, and the exact format for numbers, bearings, dates, positions, speeds and times; and Chapter V details flag signalling specifically — how to call, answer, complete and correct a signal, and the rules for spelling and for substitute flags.

2. Chapter I — Explanations and General Remarks

2.1 The purpose of the Code and its three signal types

The Code follows one basic principle throughout: every signal must carry a complete meaning by itself. To keep the book usable, the signals it defines fall into three lengths, each reserved for a different kind of content.

2.2 Complements

Complements are used in certain cases, where necessary, to supplement the available groups; in the examples the Code gives, they are numerals that follow the basic group. The Code lists four things a complement expresses.

Complements that recur across many signals are not repeated everywhere in the text; they are grouped once into three reference tables, and used only where the text of a given signal specifically points to one of those tables.

2.3 Reading conventions and cross-references

Text placed in brackets inside a signal's meaning always does one of three things: it offers an alternative (for example "... (or survival craft) ..."), it flags information that may be sent if it is required or available (for example "... (position to be indicated if necessary)"), or it explains the text around it. The material itself is organised by subject and meaning, and signals are cross-referenced extensively in the right-hand column, to make coding easier.

3. Chapter II — Definitions

3.1 Who does what: signalling and station roles

Chapter II fixes the vocabulary the rest of the Code relies on for who is involved in a message and how it travels. Whoever orders a signal to be sent is the originator; the station where that message is handed in for transmission is the station of origin; the station that actually keys or hoists it out is the transmitting station. On the other end, the authority the signal is addressed to is the addressee, and the station that actually reads the incoming signal is the receiving station.

3.2 The shape of a message: groups, hoists and tacklines

A few more terms describe the physical shape a message takes once it is being sent. A hoist is one or more groups displayed from a single halyard. At the dip and close up are simply the two heights at which anything can be hoisted — about half the full extent of the halyards, and the full extent. Chapter V puts them to work: it is the receiving station's answering pendant that sits at the dip while a hoist is being read and goes close up once it is understood. When more than one group rides the same halyard, a tackline keeps them apart. A numeral group, meanwhile, is simply one or more numerals grouped together.

4. Chapter III — Methods of Signalling

4.1 The seven methods of signalling

The Code allows a signal to be made by any of seven methods. Some of the general instructions in Chapter IV are common to all of them, but two are not: how a number is signalled and how a decimal point is signalled both change with the method chosen.

4.2 Flag signalling: composition of a set

A complete set of signal flags is fixed in size and composition, and the Code sends the detailed instructions for flag signalling to Chapter V — where the substitutes below are put to use by a ship carrying only one such set.

4.3 Flashing light and sound: the Morse timing ratios

Flashing light and sound signalling both transmit letters, numerals and other symbols as dots and dashes, and the Code fixes the exact ratio of durations between them.

What Chapter III gives for flashing light and sound is the general parameter set — the ratios between the Morse elements and the standard rate — and the Code says so explicitly: the detailed instructions for these two methods sit in later chapters, outside the five covered here. The same applies to radiotelephony, whose detail the Code places in a chapter of its own.

4.4 Voice, radiotelegraphy and radiotelephony

Over a loud hailer, plain language should be used whenever possible; where a language difficulty exists, groups from the Code could be transmitted using the phonetic spelling tables. When radiotelegraphy or radiotelephony carries a signal instead, the operators involved must comply with the Radio Regulations of the International Telecommunication Union then in force.

5. Chapter IV — General Instructions

5.1 Originator, addressee and identification

Unless a signal states otherwise, every signal between vessels runs from the master of the originating vessel to the master of the vessel of destination — the Code assumes that chain of authority by default. Ships and aircraft each carry an identity signal, allocated on an international basis, and because the allocation is international the identity signal can itself indicate a ship's or aircraft's nationality; national administrations may issue their own supplementary tables showing how these signals are allocated.

An identity signal serves two distinct purposes: to speak to, or call, a station, and to speak of, or indicate, a station.

YP LABC = "I wish to communicate with vessel LABC by . . . (Complements Table I)" illustrates the first use; HY 1 LABC = "The vessel LABC with which I have been in collision has resumed her voyage" illustrates the second.

Names of vessels and places are handled differently from identity signals: they are spelt out, letter by letter, as in RV Gibraltar = "You should proceed to Gibraltar".

5.2 How to signal numbers

How a number is transmitted depends entirely on the method of signalling in use.

Where a figure is part of a signal's basic signification rather than a free-standing number, it travels together with the basic group itself: DI 20 = "I require boats for 20 persons"; FJ 2 = "Position of accident (or survival craft) is marked by sea marker". Wherever depths or similar quantities may be given in either unit, the figures are followed by "F" for feet or "M" for metres.

A decimal point between numerals has its own signal per method:

5.3 Azimuth, course and date

Three further quantities each have their own fixed figure format.

5.4 Latitude, longitude and distance

Position and distance are the format rules most worth reading in full, because more than one element may be dropped when there is no risk of confusion: the letters "N"/"S" and "E"/"W", the "R" of distance, and — in longitude only — the figure indicating hundreds of degrees, which is why longitude runs to four or, if necessary, five figures.

5.5 Speed, time, time of origin and local codes

Speed is signalled as figures preceded by one of two letters depending on the unit:

Time follows the same four-figure logic in both of its forms — the first two figures are the hour, from 00 (midnight) to 23 (11 p.m.), and the last two are the minutes, from 00 to 59 — with the prefix letter marking which time system is meant:

The time of origin is a different figure from either of these: it may be added at the end of the text, given to the nearest minute in four figures, and beyond marking when the signal was ordered it also works as a convenient reference number for the signal itself. Separately, when a vessel or coast station wants to send a signal drawn from a local code rather than from the Code proper, the signal YV 1 = "The groups which follow are from the local code" precedes it, whenever that is necessary to avoid misunderstanding.

6. Chapter V — Flag Signalling

6.1 General rule and how to call

As a general rule only one hoist should be shown at a time, and each hoist or group of hoists stays flying until the receiving station has answered it. When more than one group is shown on the same halyard, a tackline separates them. The transmitting station always hoists the signal wherever it can be seen most easily by the receiving station — a position where the flags blow out clear and stay free from smoke.

To call a station, its identity signal is hoisted together with the signal itself. If no identity signal is hoisted at all, the signal is understood to be addressed to every station within visual signalling distance. When the identity signal of the intended station cannot be determined, one of the following groups is hoisted first, while the calling station hoists its own identity signal at the same time:

6.2 How to answer and complete a signal

Every station a signal is addressed to, or that a signal indicates, hoists the answering pendant at the dip as soon as it sees each hoist, and close up as soon as it understands that hoist. Once the transmitting station hauls the hoist down, the answering pendant returns to the dip, then goes close up again as soon as the next hoist is understood. To mark the end of the whole signal, the transmitting station hoists the answering pendant singly after the last hoist; the receiving station answers that closing hoist exactly as it answered every other one.

6.3 When a signal is not understood

If the receiving station cannot clearly make out the signal at all, it simply keeps the answering pendant at the dip. If it can make out the signal but not what it means, it hoists one of two signals instead:

6.4 The use of substitutes

A substitute lets one signal flag — an alphabetical flag or a numeral pendant — be repeated inside the same group by a ship that carries only one set of flags. The full rule below is reproduced verbatim, and none of its five sentences can be dropped when reading it back: what substitutes are for, what the first substitute repeats, what the second and third repeat, the ban on using a substitute twice in one group, and the answering pendant that is skipped in the count.

6.5 How to spell and the Code Pendant

Names appearing in the text of a signal are spelt out using the alphabetical flags; and the signal YZ = "The words which follow are in plain language" can be used, if necessary. Separately, when a ship of war wants to communicate with a merchant vessel, she hoists the Code Pendant in a conspicuous position and keeps it flying for the whole time the signal is being made.