Module 15 - Restricted Visibility
Fog Signals (Rule 35)
What you will learn
Select the prescribed Rule 35 signal from actual vessel status, making-way state and length, including the under-12-metre alternative and motorsailing boundary.
Rule 35 signals are made in or near restricted visibility by day or night. The stated interval is a maximum—'not more than'—rather than an instruction to wait exactly two minutes or one minute.
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. It remains underway because it is not anchored, aground or made fast to the shore.
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 while under sail and not using propulsion machinery. When the engine propels it, use power-driven status even if sails are set.
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 forward and a gong rapidly aft immediately afterwards. 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 the prescribed signals, but if it does not, it must make another efficient sound signal at intervals of not more than two minutes.
| Vessel status | Signal | Maximum interval |
|---|---|---|
| Power-driven, making way | One prolonged blast | Not more than 2 minutes |
| Power-driven, underway but 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+ also rapid gong aft | Not more than 1 minute |
| Aground | Three distinct strokes, rapid bell, three distinct strokes; gong if required | Not more than 1 minute |
| Under 12 m when not giving the prescribed signal | Another efficient sound signal | Not more than 2 minutes |
Classify the yacht each time its status changes
A 10-metre yacht motorsails in mist, stops making way while still underway, switches the engine off and sails, then anchors. It has an efficient horn but no prescribed bell appliance.
1. Motorsailing and moving
Use the power-driven making-way signal: one prolonged at intervals of not more than two minutes.
2. Underway but stopped
Use two prolonged blasts about two seconds apart at intervals of not more than two minutes.
3. Under sail alone
After propulsion machinery is no longer used, sound one prolonged followed by two short blasts.
4. At anchor under 12 metres
Give the prescribed signal if suitably equipped or another efficient sound signal at intervals of not more than two minutes.
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.
- Using the sailing-vessel signal while propulsion machinery is being used.
- Confusing a power-driven vessel stopped in the water with a vessel at anchor; the former remains underway.
- Assuming a vessel under 12 metres may remain silent because it need not give every prescribed signal.
Recap
- Choose the signal from actual status, making-way state and length.
- The stated interval is a maximum and the signals apply in or near restricted visibility.
- A motorsailing yacht is power-driven; an under-12-metre vessel must still make an efficient signal.
Optional quick check
Section 3 of 8
A 10-metre yacht is moving under sail with its engine also propelling it. Which Rule 35 status applies?
Sources and factual review
Reviewed 2 September 2026 - Compass Revision editorial review.
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