One Prolonged Blast Every Two Minutes

One Prolonged Blast Every Two Minutes is an important safety measure to take when operating a power-driven vessel. This signal indicates that the power-driven vessel is underway, and it is used to warn other vessels in the area. It is important to be aware of this signal, and to take appropriate measures when hearing it.

If you’re a maritime enthusiast, then you know what a fog horn is. For the rest of us, a fog horn is a loud horn that ships use to warn other vessels of their presence in dense fog. Fog horns are typically operated manually, but some newer models are automated.

Fog horns are generally used in areas where there is a high risk of collision, such as narrow channels or shipping lanes. They can also be used to alert vessels to the presence of icebergs or other hazards. Fog horns are usually sounded in a pattern of one prolonged blast or one prolonged blast followed by two short blasts every two minutes.

This allows other vessels time to react and avoid collision. If you’re ever out on the water in dense fog, keep your ears open for the sound of fog horns. And if you hear one, be sure to give yourself plenty of time and space to react accordingly.

One Prolonged Blast Every Two Minutes


What Does One Prolonged Blast Every Two Minutes Mean?

If you hear one prolonged blast every two minutes, it means that a vessel is seeking passage through an area of restricted visibility. Only one prolonged blast at intervals of not more than 2 minutes is used by power vessels when they are at underway.

For your information, One prolonged blast timing is: 4-6 seconds. Don’t get it confused with short blast which timing is one second only.

What Vessel Sounds One Prolonged Blast at Intervals of Not More Than 2 Minutes?

Power-driven vessels use “one prolonged blast at intervals of not more than 2 minutes” to warn other vessels around them to stay safe.

A vessel that is required to sound one prolonged blast at intervals of not more than 2 minutes is a power-driven vessel that is underway but not making way through the water. This type of vessel must also exhibit navigation lights.

What Does One Prolonged Blast Indicate?

According to the International Regulations for Preventing Collisions at Sea (COLREGs), a prolonged blast from a ship’s horn indicates that the vessel is about to cross another vessel’s path. It is also a warning signal used by power-vessel to warn any vessel about their present situation. The situations when it is required to warn only when a vessel coming from a blind sector or leaving the jetty.

The COLREGs are an international maritime law that governs how vessels must conduct themselves in order to avoid collisions.

Maritime sound signals

You are Out on the Water in Foggy Conditions You Hear One Prolonged Blast Every Two Minutes

If you find yourself out on the water in foggy conditions, there are some important things to keep in mind. For starters, you should be aware that navigation can be very difficult in these conditions. If possible, it’s best to stay close to shore or other landmarks that you can easily identify.

Additionally, it’s important to listen for navigational signals. You may hear one prolonged blast every two minutes, which indicates the presence of another vessel nearby. If you do hear this signal, it’s important to take caution and avoid collision.


If you’re ever in a situation where you need to call for help, make sure to use the internationally recognized distress signal: six short blasts followed by one long blast on your horn or whistle, repeated every two minutes.

Related: You are Underway in Restricted Visibility You Hear the Fog Signal of Another Vessel

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