What does 7 blasts on a ship horn mean?

[OChristopher]

Seven short blasts followed by one long blast on a ship’s horn is a critical sound signal defined by the International Regulations for Preventing Collisions at Sea (COLREGs). It specifically means: “I am operating in restricted visibility and am not under command, restricted in my ability to manoeuvre, or otherwise unable to manoeuvre as required by these Rules.” This signal is exclusively used when a vessel is in or near an area of fog, mist, or other conditions limiting visibility, and its manoeuvrability is severely compromised.

The signal’s structure is precise. The seven short blasts (each about one second in duration) immediately grab attention and indicate an urgent situation. The concluding long blast (lasting four to six seconds) confirms the context of restricted visibility. This combination separates it from other signals. For instance, one prolonged blast is used by power-driven vessels making way through fog, while two prolonged blasts indicate a vessel underway but stopped. The 7+1 signal is reserved for vessels with impaired manoeuvring in poor visibility.

Understanding this requires knowing the vessel’s status. A vessel “not under command” (NUC) has a mechanical failure preventing standard steering. A vessel “restricted in its ability to manoeuvre” (RAM) is engaged in work like cable-laying or dredging. The 7+1 blast signal alerts all nearby ships that this vessel cannot take standard avoiding actions. According to industry practice and COLREGs training, upon hearing this signal, other vessels must immediately proceed with extreme caution, reduce speed to a minimum, and be prepared to stop until the risk of collision is clear.

The importance of this signal in collision avoidance cannot be overstated. In dense fog where visual contact is zero, sound signals become the primary navigation tool. Misinterpretation can lead to catastrophic collisions. Data from maritime incident reports, such as those analyzed by organizations like the International Maritime Organization (IMO), show that confusion over sound signals contributes to a percentage of collision incidents in low visibility. The table below clarifies the distinction:

Signal Pattern	Typical Meaning	Key Context
One prolonged blast	"I am a power-driven vessel making way through the fog."	Restricted visibility, normal manoeuvrability.
Two prolonged blasts	"I am a power-driven vessel underway but stopped in the fog."	Restricted visibility, no way on.
Seven short + One long blast	"I am in fog and cannot manoeuvre as required by the rules."	Restricted visibility AND impaired manoeuvrability.

In practice, hearing this signal means you are near a potential hazard. The correct response is to navigate with the utmost care, determine the other vessel’s location if possible via radar, and avoid making assumptions about its course or speed. The signal is a clear declaration of vulnerability and a legal requirement under COLREGs Rule 35(c), making its accurate recognition a fundamental skill for all mariners.

[VanAustin]

As a deck officer, I’ve had to sound this signal in thick fog when our steering gear failed. It’s a serious call. Those seven quick blasts tell everyone, “Heads up, emergency here,” and the long blast ties it to the fog. You’re telling the whole area that you’re both blind and crippled. When you hear it from another ship, your first move is to slow right down and get on the radio. It’s not just a noise; it’s a legal warning that the normal rules of the road are off the table.

[AllisonAnn]

I remember during my cadet training, the master drilled this into us. “Seven short and one long,” he’d say. “That’s the ‘I’m in trouble and I can’t see’ signal.” It stuck with me because it’s so specific. It doesn’t just say there’s fog; lots of ships are in fog. It says this particular ship in the fog can’t get out of your way. Maybe its engine is gone, or it’s towing something huge. Hearing it means you become the responsible party to avoid a crash. You can’t expect them to move. It’s a signal that passes the burden of collision avoidance onto you, so you listen for it with your whole attention.

[McDakota]

Think of it as a distress signal for manoeuvring. The fog means you can’t see, and the seven-and-one combo means the ship making the noise can’t steer properly either. It’s a double problem. If you’re on a smaller boat and hear this from a large tanker or cargo ship, you need to give it a very wide berth immediately. That ship legally cannot take evasive action. Your job is to stay clear. It’s one of the most urgent signals in the rulebook, used only in the worst visibility when a ship is at its most vulnerable.

[EmmaFitz]

From the bridge perspective, using this signal is a major decision. You’re publicly declaring an emergency situation. We use it only when two conditions are met simultaneously: visibility is severely reduced, and we have a verified propulsion or steering failure that leaves us dead in the water or unable to execute standard manoeuvres. The sequence is intentional—the rapid seven blasts are an alarm, the long blast provides context. When we hear it from another vessel, all non-essential bridge conversation stops. We plot its position on radar, sound one prolonged blast ourselves to announce our presence, and reduce speed to bare steerageway. The goal is to buy time and distance. We also immediately attempt VHF radio contact to coordinate intentions, but we never assume they can hear or respond. The signal overrides all standard crossing or overtaking rules; safety dictates absolute caution until the vessel is located and clear.