Module 15 - Restricted Visibility
Fog Signals (Rule 35)
What you will learn
Select the prescribed Rule 35 signal from the vessel's actual status, including the small-vessel boundary and the effect of using propulsion machinery while sailing.
Rule 35 signals are made in or near restricted visibility, by day or night. The interval is a maximum: 'not more than two minutes' or 'not more than one minute' does not mean waiting exactly that long in every circumstance.
A power-driven vessel making way through the water sounds one prolonged blast at intervals of not more than two minutes. A power-driven vessel underway but stopped and making no way sounds two prolonged blasts in succession, about two seconds apart, at intervals of not more than two minutes. 'Underway' means not at anchor, made fast to the shore or aground; 'making way' means moving through the water.
A vessel not under command, restricted in ability to manoeuvre, constrained by draught, sailing, fishing, or towing or pushing another vessel sounds one prolonged followed by two short blasts at intervals of not more than two minutes instead of the power-driven signals. A yacht is a sailing vessel for this purpose only when under sail and not using propulsion machinery. If the engine is being used for propulsion, apply the power-driven status and signal.
A vessel at anchor rings the bell rapidly for about five seconds at intervals of not more than one minute. At 100 metres or more, the bell is sounded in the forepart and a gong rapidly aft for about five seconds immediately afterward. A vessel aground adds three separate and distinct bell strokes immediately before and after the rapid ringing. A vessel under 12 metres is not obliged to give those prescribed Rule 35 signals, but if it does not, it must make another efficient sound signal at intervals of not more than two minutes; Rule 33 also requires an efficient means of making sound.
| Vessel status | Prescribed signal | Maximum interval |
|---|---|---|
| Power-driven, making way | One prolonged blast | Not more than 2 minutes |
| Power-driven, underway but stopped and making no way | Two prolonged blasts, about 2 seconds apart | Not more than 2 minutes |
| Sailing; fishing; NUC; RAM; constrained by draught; towing or pushing | One prolonged followed by two short blasts | Not more than 2 minutes |
| At anchor | Rapid bell for about 5 seconds; 100 m+ adds rapid gong aft | Not more than 1 minute |
| Aground | Three distinct bell strokes, rapid bell, three distinct strokes; gong if required | Not more than 1 minute |
| Under 12 m when not making the prescribed signal | Some other efficient sound signal | Not more than 2 minutes |
Classify before sounding
A 10-metre sailing yacht motorsails in mist, then switches the engine off and continues under sail. Later it anchors. The crew have a working horn but no prescribed bell appliance.
1. While motoring
Treat the yacht as power-driven: one prolonged if making way, or two prolonged if underway but stopped and making no way.
2. Under sail only
After propulsion machinery is no longer being used, use one prolonged followed by two short blasts.
3. At anchor
Because the yacht is under 12 metres, either give the prescribed anchor signal if suitably equipped or make another efficient sound signal at intervals of not more than two minutes.
4. Keep listening
Continue the proper lookout and Rule 19 response; sounding the correct signal does not establish that another vessel has heard or located it.
Sense check: Sails being set do not make a yacht a sailing vessel under the Rules while propulsion machinery is also being used.
Common mistake or limitation
- Remembering the interval as exactly two minutes or one minute instead of the maximum permitted interval 'not more than'.
- Using the sailing-vessel signal while motorsailing with propulsion machinery in use.
- Confusing a power-driven vessel stopped in the water with a vessel at anchor; the former remains underway and sounds two prolonged blasts.
- Assuming a vessel under 12 metres may remain silent because it need not carry or use every prescribed appliance.
Recap
- Choose the signal from vessel status and whether it is making way, stopped, anchored or aground.
- The stated interval is a maximum, and the signals apply in or near restricted visibility.
- A yacht using propulsion machinery is power-driven; a vessel under 12 metres must still make an efficient signal if not making the prescribed one.
Optional quick check
Section 3 of 5
A yacht has sails set and is using its engine for propulsion in fog. Which status governs its Rule 35 signal?
Sources and factual review
Reviewed 1 September 2026 - Day Skipper Revision.
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