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35

Sound Signals in Restricted Visibility

In restricted visibility, power-driven vessels making way sound one prolonged blast every 2 minutes. Vessels not making way sound two prolonged blasts.

Rule 35 prescribes fog signals in restricted visibility.

a
A power-driven vessel making way through the water sounds one prolonged blast at intervals of not more than 2 minutes.
b
A power-driven vessel underway but stopped and not making way sounds two prolonged blasts in succession at intervals of not more than 2 minutes.
c
A vessel not under command, restricted in her ability to manoeuvre, constrained by draught, sailing, engaged in fishing, or towing/pushing another vessel sounds one prolonged followed by two short blasts at intervals of not more than 2 minutes.
d
The last vessel of a tow, if manned, shall where practicable sound one prolonged followed by three short blasts.
e
A vessel at anchor shall ring the bell rapidly for about 5 seconds at intervals of not more than one minute; a vessel of 100 metres or more also sounds the gong aft. She may in addition sound one short, one prolonged and one short blast to warn of her position and of possible collision.
f
A vessel aground gives the anchor bell signal, adds three distinct strokes before and after the rapid ringing, and may also sound one short, one prolonged and one short 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

Underway and making way: 1 prolonged every 2 minutes

2

Underway but stopped: 2 prolonged in succession every 2 minutes

3

Special-status vessels: 1 prolonged plus 2 short every 2 minutes

4

Anchor signals use the bell every minute, not the 2-minute whistle interval

Common Mistakes

Forgetting to change from one prolonged to two prolonged blasts when the ship stops making way

Mixing up anchor bell signals with underway fog signals

Ignoring the optional short-prolonged-short warning that an anchored or aground vessel may also use

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