Sound Signals at Sea: What Horn Blasts Really Mean

When two vessels close in on each other, especially in busy water or poor visibility, a horn can say what a shout never could. Sound signals are the COLREGs’ way of announcing your intentions and your presence, and they are built from a tiny vocabulary of blasts. Once you know that vocabulary, the honking you hear around a harbour entrance stops being noise and starts being a conversation you can follow.

This guide breaks down the two basic building blocks of every signal, the manoeuvring signals vessels use when they can see each other, the overtaking signals used in narrow channels, and the distinctive fog signals used when visibility is poor. It is a favourite exam topic because the signals are precise and easy to test.

The Two Building Blocks: Short and Prolonged Blasts

Every sound signal in the COLREGs is made from just two elements, so learn these first and everything else follows.

• A short blast lasts about one second.
• A prolonged blast lasts about four to six seconds.

That is the entire alphabet. All the meanings come from how many blasts you make and whether they are short or prolonged. Vessels of different sizes carry different sound-making equipment: larger vessels have a whistle and a bell, and the biggest also carry a gong, but for recreational purposes the short and prolonged blast are what you need to master.

Manoeuvring Signals When Vessels Are in Sight

When power-driven vessels are in sight of one another and one is altering course or manoeuvring, it announces the manoeuvre with short blasts on the whistle. These signals tell the other skipper exactly what you are doing.

• One short blast means “I am altering my course to starboard” (to the right).
• Two short blasts mean “I am altering my course to port” (to the left).
• Three short blasts mean “I am operating astern propulsion,” in other words I am going into reverse. Note this does not necessarily mean the vessel is moving backwards, only that its engines are working astern.

There is also a warning signal for when you cannot understand another vessel’s intentions or doubt whether it is taking enough action to avoid a collision. This is five (or more) short and rapid blasts, sometimes called the doubt or danger signal. If you hear five rapid blasts, treat it as a serious alert that something is wrong with the developing situation.

Overtaking Signals in a Narrow Channel

In a narrow channel or fairway, overtaking safely requires cooperation, and the COLREGs give vessels a way to agree on it by sound. A vessel that intends to overtake another sounds a signal to indicate which side it means to pass.

• Two prolonged blasts followed by one short blast means “I intend to overtake you on your starboard side.”
• Two prolonged blasts followed by two short blasts means “I intend to overtake you on your port side.”

The vessel being overtaken, if it agrees, replies with one prolonged, one short, one prolonged and one short blast in that order, signalling agreement. If it does not agree, or is unsure, it may sound the five-short-blast doubt signal instead. This little exchange lets two vessels arrange a safe overtake without a word being spoken.

Signals in Restricted Visibility

When fog, heavy rain or darkness reduce visibility, vessels cannot rely on being seen, so they announce their presence and status with distinctive sound signals repeated at intervals of not more than two minutes. These are different from the manoeuvring signals above because they say what a vessel is rather than what it is about to do.

A power-driven vessel making way through the water sounds one prolonged blast every two minutes or less. A power-driven vessel underway but stopped and making no way sounds two prolonged blasts with a short gap between them. A sailing vessel, a fishing vessel, a vessel not under command, a vessel restricted in her ability to manoeuvre, and a vessel towing all sound the same distinctive signal: one prolonged blast followed by two short blasts. A vessel at anchor in fog rings its bell rapidly for about five seconds every minute, and a large vessel may add other sounds. Learning which signal goes with which situation is worth the effort, because restricted-visibility questions are common.

Making the Signals Second Nature

The reason sound signals are so testable is that they are exact: a specific number of specific blasts means a specific thing. The good news is that this precision also makes them easy to drill. Repeat the short-and-prolonged patterns until “one short equals turning to starboard” and “five short equals danger” are automatic. In the boatingexamine course you can practise sound-signal questions in exam format, including the overtaking exchange and the fog signals, so the meanings come to you instantly.

FAQ

What do five short blasts mean? Five (or more) short, rapid blasts are the doubt or danger signal. A vessel sounds it when it cannot understand another vessel’s intentions or doubts whether enough is being done to avoid a collision. If you hear it, assume the situation is not safe and act accordingly.

Does three short blasts mean the vessel is going backwards? Three short blasts mean the vessel is operating astern propulsion, that is, its engines are working in reverse. This is often used to stop or back up, but the signal strictly refers to the engines being put astern, not to the vessel’s actual movement through the water.

How often are fog signals repeated? Signals in restricted visibility are sounded at intervals of not more than two minutes. A vessel at anchor sounds its bell signal at intervals of not more than one minute. Keeping to these intervals lets other vessels track your position and status even when they cannot see you.