IALACOLREG
Start Quiz
34

Manoeuvring and Warning Signals

One short blast means starboard, two means port, three means astern propulsion, and five or more rapid blasts mean doubt or danger.

Rule 34 prescribes manoeuvring and warning signals for vessels in sight of one another.

a
The basic signals are: - One short blast: I am altering my course to starboard - Two short blasts: I am altering my course to port - Three short blasts: I am operating astern propulsion
b
These whistle signals may be supplemented by equivalent light signals.
c
In narrow channels and fairways, special signals are used for overtaking: two prolonged plus one short blast to overtake on the other vessel's starboard side, and two prolonged plus two short blasts to overtake on her port side. The vessel being overtaken answers with one prolonged, one short, one prolonged and one short if she agrees.
d
If a vessel does not understand the other vessel's intentions, or doubts whether sufficient action is being taken, she shall sound at least five short and rapid blasts.
e
A vessel nearing a bend or area of a channel where another vessel may be hidden by an obstruction shall sound one prolonged blast; any approaching vessel that hears it shall answer with a prolonged blast.

Signal Workflow

1

Decide the context first: manoeuvring in sight, restricted visibility, or distress. The same whistle can mean very different things in a different context.

2

Check both the pattern and the interval. For fog signals, the time spacing is part of the rule, not just the blast sequence.

3

When in doubt about another vessel's intentions, use the prescribed warning signal early rather than waiting for the situation to deteriorate.

Exam Focus

1

Three short blasts are astern propulsion, not a fog signal.

2

In restricted visibility, think 'every two minutes' for underway signals and 'every one minute' for anchor bell signals.

Key Takeaways

1

1 short = starboard, 2 short = port, 3 short = astern propulsion

2

5 or more rapid blasts are the doubt or danger signal

3

Channel overtaking uses the prolonged-plus-short combinations, not the basic one- and two-blast signals

4

A single prolonged blast warns of a blind bend or obstruction in a channel

Common Mistakes

Using the basic manoeuvring blasts when the channel overtaking signals are required

Confusing three short blasts with a fog signal

Forgetting that Rule 34 depends on vessels being in sight, except for the bend signal

Test Your Knowledge

Test your knowledge and prove your mastery.