Part D — Sound and Light Signals
COLREGS Rule 35 — Sound Signals in Restricted Visibility
Rule 35 specifies the fog signals that vessels must make in or near an area of restricted visibility. The signals vary by vessel type and whether the vessel is making way, stopped, or engaged in special operations. All signals are given at intervals of not more than 2 minutes.
Rule Text
In or near an area of restricted visibility: a power-driven vessel making way through the water shall sound one prolonged blast at intervals of not more than 2 minutes; a power-driven vessel underway but stopped and making no way through the water shall sound two prolonged blasts at intervals of not more than 2 minutes, with an interval of about 2 seconds between the blasts; a vessel not under command, restricted in ability to maneuver, constrained by draft, a sailing vessel, a vessel engaged in fishing, or a vessel engaged in towing or pushing, shall sound one prolonged and two short blasts at intervals of not more than 2 minutes.
What it means on the water
- →Power-driven making way: 1 prolonged blast every ≤2 minutes.
- →Power-driven stopped (no way): 2 prolonged blasts (~2 sec apart) every ≤2 minutes.
- →Sailing vessel, fishing vessel, NUC, RAM, CBD, towing/pushing: 1 prolonged + 2 short every ≤2 minutes.
- →Vessel at anchor < 100m: rapid bell ringing for ≥5 seconds every minute.
- →Vessel at anchor ≥ 100m: rapid bell forward + rapid gong aft, ≥5 seconds every minute.
- →Vessel aground: bell signal + 3 separate bell strokes before and after.
Common exam mistakes
- ✗Giving a stopped power-driven vessel 1 prolonged blast — stopped vessels sound 2 prolonged blasts.
- ✗Applying the power-driven making-way signal (1 prolonged) to sailing vessels — they sound 1 prolonged + 2 short.
- ✗Missing the anchor signal requirements — these are frequently tested separately.
USCG exam questions — Rule 35
These questions are drawn from the same pool used in real USCG licensing exams. Correct answers and explanations are shown.
1. Under the COLREGS, what is the duration of a 'short blast' on a sound signal appliance?
- A.About 1 second✓
- B.About 4 seconds
- C.About 6 seconds
- D.About 2 seconds
Why: Rule 32(b) defines a short blast as a blast of about one second's duration. A prolonged blast, by contrast, lasts 4 to 6 seconds. Mixing up these durations is the most common error on the exam.
2. Under Rule 33, a vessel under 12 meters in length is required to carry which sound signal equipment?
- A.A whistle and a bell
- B.A whistle, bell, and gong
- C.Some means of making an efficient sound signal✓
- D.Nothing — vessels under 12 meters are exempt
Why: Rule 33(b) states that a vessel of less than 12 meters is not obliged to carry the prescribed appliances but shall have some means of making an efficient sound signal. The rule does not specify the device, but it must be capable of giving the required signals.
3. A vessel at anchor in restricted visibility must give what sound signal?
- A.One prolonged blast every 2 minutes
- B.Rapid ringing of a bell for about 5 seconds at intervals of not more than 1 minute✓
- C.Two short blasts every 2 minutes
- D.One prolonged followed by two short blasts every 2 minutes
Why: Rule 35(g) requires a vessel at anchor to ring the bell rapidly for about 5 seconds at intervals not exceeding 1 minute. On a vessel 100 meters or more, the bell is rung in the forepart of the vessel and is followed immediately by a rapid gong stroke in the after part. Additionally, a vessel at anchor may sound three blasts (short, prolonged, short) as a warning to an approaching vessel.
4. In restricted visibility, a vessel engaged in fishing is underway and making way. What fog signal does she sound?
- A.One prolonged blast every 2 minutes
- B.Two prolonged blasts every 2 minutes
- C.One prolonged blast followed by two short blasts every 2 minutes✓
- D.Four short blasts every 2 minutes
Why: A vessel engaged in fishing is listed in Rule 35(c) and sounds one prolonged blast followed by two short blasts at intervals not exceeding 2 minutes, regardless of whether she is making way or stopped (she is still 'underway'). This is the same signal as NUC, RAM, sailing, and towing vessels.
5. An anchored vessel wishing to warn an approaching vessel in fog may supplement the bell signal with which optional whistle signal?
- A.One prolonged blast
- B.Two prolonged blasts
- C.One short, one prolonged, and one short blast on the whistle✓
- D.Five short blasts
Why: Rule 35(g) permits an anchored vessel, in addition to the mandatory rapid bell ringing, to sound a whistle signal of one short blast, one prolonged blast, and one short blast (·−·) as a warning to an approaching vessel. This is optional and supplements — it does not replace — the bell signal.
6. A power-driven vessel underway but stopped and making no way through the water in restricted visibility shall sound which fog signal?
- A.One prolonged blast every 2 minutes
- B.Two prolonged blasts every 2 minutes✓
- C.One prolonged and two short blasts every 2 minutes
- D.Rapid ringing of a bell for 5 seconds every minute
Why: Rule 35(b) specifies that a power-driven vessel underway but stopped and making no way shall sound two prolonged blasts in succession at intervals of not more than 2 minutes, with an interval of about 2 seconds between blasts.
7. A vessel aground in restricted visibility must sound which fog signal in addition to the bell signal?
- A.Three separate and distinct strokes on the bell before and after the rapid ringing✓
- B.One prolonged blast every 2 minutes
- C.Two prolonged blasts every 2 minutes
- D.A gong signal only
Why: Rule 35(h) requires a vessel aground to give the bell signal prescribed for anchored vessels AND additionally to give three separate and distinct strokes on the bell immediately before and after the rapid ringing of the bell.
8. How long is a 'prolonged blast' as defined in the COLREGS, and how does this differ from a 'short blast'?
- A.Prolonged = 4 to 6 seconds; short = about 1 second✓
- B.Prolonged = 6 to 8 seconds; short = about 2 seconds
- C.Prolonged = 2 to 4 seconds; short = about 0.5 seconds
- D.Prolonged = 8 to 10 seconds; short = about 1 second
Why: Rule 32(b) and (c) define a prolonged blast as a blast of 4 to 6 seconds duration, and a short blast as a blast of about 1 second duration. These definitions are fundamental to applying all sound signaling rules correctly.
Frequently asked questions
- What fog signal does a power-driven vessel making way sound?
- A power-driven vessel making way through the water sounds one prolonged blast at intervals of not more than 2 minutes. If that same vessel is underway but stopped and not moving through the water, it sounds two prolonged blasts separated by about 2 seconds, also at intervals of not more than 2 minutes.
- What fog signal does a sailing vessel sound in restricted visibility?
- A sailing vessel underway sounds one prolonged blast followed by two short blasts at intervals of not more than 2 minutes. This same signal is used by NUC vessels, RAM vessels, vessels constrained by draft, fishing vessels, and vessels towing or pushing.
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