Sound signals are a perennial topic in the SBF theory exam – and a popular source of mistakes. The reason: on the maritime waterways (COLREGs) the same blast sequences sometimes mean something different than on the inland waterways. This article sorts the most important signals cleanly into Coastal and Inland – and shows where the mix-up traps lie.
Short blast, prolonged blast: the basics
Before we get to the meaning, you need the two building blocks:
- Short blast (●): lasts about one second.
- Prolonged blast (▬): lasts about four to six seconds.
All sound signals are made up of these two building blocks. What’s tested is hearing and matching them – in the exam you have to know the meaning of a given blast sequence.
Sound signals at sea (COLREGs)
On the maritime waterways the Collision Regulations (COLREGs) apply. Here a distinction is made between maneuvering and warning signals (when vessels are in sight of one another) and signals in restricted visibility.
Maneuvering and warning signals (vessels in sight)
A power-driven vessel gives these signals when it maneuvers within sight of another:
| Signal | Meaning |
|---|---|
| ● | I am altering my course to starboard |
| ● ● | I am altering my course to port |
| ● ● ● | I am operating astern propulsion |
| ● ● ● ● ● (at least 5 short) | Doubt/warning signal: I do not understand your intentions / risk of collision |
| ▬ (one prolonged blast) | Warning signal at blind spots and bends – whoever hears it answers with the same signal |
In narrow channels there are also overtaking signals: ▬ ▬ ● (“I intend to overtake you on your starboard side”), ▬ ▬ ● ● (”… on your port side”) and ▬ ● ▬ ● (“agreement to be overtaken”).
Signals in restricted visibility
“Restricted visibility” means visibility limited by fog, rain, snow or “thick weather”. These signals serve the single message “I am here” and are mandatory – they’re given at least every two minutes:
| Signal | Meaning |
|---|---|
| ▬ | Power-driven vessel making way through the water |
| ▬ ▬ | Power-driven vessel underway that has stopped (not making way through the water) |
| ▬ ● ● | Sailing vessel; also vessels fishing, not under command, restricted in their ability to maneuver, constrained by their draft, and towing/pushing vessels |
| ▬ ● ● ● | A towed vessel, or the last vessel of a tow, if manned |
A vessel at anchor instead draws attention to itself by ringing the bell (about five seconds, at least every minute).
Sound signals on inland waters
On the inland waterways the COLREGs do not apply, but rather the Inland Waterways Regulations. For small craft these signals are important:
| Signal | Meaning |
|---|---|
| ▬ (one prolonged blast) | Attention |
| ● | I am directing my course to starboard |
| ● ● | I am directing my course to port |
| ● ● ● | My engine is going astern |
| ● ● ● ● | I am unable to maneuver |
| ● ● ● ● ● | I cannot be overtaken |
| at least 6 very short blasts | Risk of collision |
| ● ▬ ● ▬ … (short, prolonged, …) | Stay-away signal (e.g. for escaping hazardous substances) |
The most common mix-up traps
This is exactly where most exam mistakes happen:
- ● ● ● ● (four short blasts): On Inland this means “I am unable to maneuver”. In the COLREGs at sea there is no such four-blast signal – there the relevant warning signal is at least five short blasts.
- ● ● ● ● ● (five short blasts): At sea this is the doubt/warning signal. On Inland the same blast sequence means “I cannot be overtaken”.
- Prolonged blast (▬): At sea a warning signal at blind spots, on inland the general attention signal.
So always remember first: am I at sea or on inland waters? Only then do you match the blast sequence.
How to learn sound signals properly
Sound signals are pure memorization with understanding. It’s best to internalize the logic (one short blast = a course change to starboard, two short = to port) and then specifically practice the differences between Coastal and Inland. In the Boatpass app you can train exactly these questions repeatedly and focus your mistake training on the signals that aren’t solid yet.
Closely related are the visual counterparts – the lights and shapes of other vessels. How to tell them apart at night is covered in our article Navigation lights explained. And which sounds apply in an emergency is in our post on distress signals at sea.
Conclusion
Sound signals are no mystery if you cleanly separate Coastal and Inland. Short blast ≈ 1 second, prolonged blast ≈ 4–6 seconds – and then: one short blast means starboard, two short means port, three short means engine astern. The few points where Coastal and Inland differ you learn specifically – then the sound-signal questions are safe points in the exam.