It has several meanings depending on circumstances.
A vessel not under command or restricted in its ability to manoeuvre, or constrained by her draught, or engaged in fishing, or towing or pushing, or a sailing vessel.
The sound signals that it is a sailing vessel underway when you hear one prolonged blast plus two short blasts every two minutes.
When visibility is very limited, such as in heavy fog, boaters must give an audible signal to others in the area. For a sailboat the signal is one prolonged blast plus two short blasts every two minutes.
The sound signals that it is a sailing vessel underway when you hear one prolonged blast plus two short blasts every two minutes.
One prolonged blast plus two short blasts every two minutes
Sailboat
During periods of restricted visibility, vessels must emit one prolonged blast followed by two short blasts every two minutes to signal their presence and intentions to other nearby vessels. This sound signal helps ensure safety and awareness in conditions where visual communication is limited. The prolonged blast alerts other vessels of the ship's position, while the two short blasts indicate that the vessel is underway. These signals are part of the International Regulations for Preventing Collisions at Sea (COLREGs).
One prolonged blast followed two short blasts, every two minutes, not to exceed two minutes. Rule 35-Sound Signals in restricted visibility.
One prolonged blast followed by two short blasts every two minutes is a sound signal used by vessels in fog or low visibility conditions. This signal indicates that the boat is under way and making way through the water. It serves to alert other vessels in the area of its presence and movement to help prevent collisions.
Rules of the Road. Rule 35, Sound Signals in Restricted Visibility. (C) A vessel not under command, a vessel restricted in her ability to maneuver, a vessel constrained by her draft, a sailing vessel, a vessel engaged in fishing, and a vessel engaged in towing or pushing another vessel SHALL, sound at intervals of not more than two minutes three blast in succession, namely one prolonged followed by two short blast.
In reduced visibility, a power-driven vessel underway is required to sound one prolonged blast followed by two short blasts every two minutes. This signal indicates its presence to other vessels in the area. The prolonged blast lasts about four to six seconds, while the short blasts last about one second each. This signaling helps to prevent collisions in situations where visibility is limited.
The sound signal of one prolonged blast followed by two short blasts every two minutes indicates that a vessel is restricted in its ability to maneuver. This signal is used to alert other vessels in the area of the restricted vessel's presence, especially in low visibility conditions like fog. It is important for nearby vessels to be cautious and maintain a safe distance from the restricted vessel.
In restricted visibility, a power-driven vessel underway is required to sound one prolonged blast every two minutes. This signal alerts other vessels to its presence and intentions. Additionally, if the vessel is making way through the water, it may also sound two short blasts after the prolonged blast.