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A power-driven vessel under way sounds one prolonged blast not less than every two minutes. However if it is less than 12meters in length it is not required to give any signal.
Rule 35 part c of the International Regulations for Preventing Collisions at Sea (72 COLREGS) states that when in restricted visibility (i.e. fog) a sailing vessel is required to sound one prolonged blast followed by two short blasts on the vessel's whistle, at intervals of not more than two minutes. Please refer to the link below.
The sound signal that you should hear when a power boat is in the fog is one prolonged blast at intervals of no more than 2 minutes.
I am a power-driven vessel underway. Sound signals let other boaters know where you are located during periods of restricted visibility, such as extreme fog. If you hear the fog signal of a vessel you cannot see, slow to a minimum speed until you are sure there is not a risk of collision. One prolonged blast at intervals of not more than two minutes is the signal used by power-driven vessels when underway.
I am a power-driven vessel underway. Sound signals let other boaters know where you are located during periods of restricted visibility, such as extreme fog. If you hear the fog signal of a vessel you cannot see, slow to a minimum speed until you are sure there is not a risk of collision. One prolonged blast at intervals of not more than two minutes is the signal used by power-driven vessels when underway.
One prolonged blast followed two short blasts, every two minutes, not to exceed two minutes. Rule 35-Sound Signals in restricted visibility.
Rules of the RoadRule 35Sound 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 blasts.
A sailing vessel making way should signal, long-short-short every two minutes in fog.
One prolonged blast plus two short blasts every two minutes. Explanation: Sound signals let other boaters know where you are located during periods of restricted visibility, such as extreme fog. If you hear the fog signal of a vessel you cannot see, slow to a minimum speed until you are sure there is not a risk of collision. One prolonged blast plus two short blasts at intervals of not more than two minutes is the signal used by sailing vessels.
One prolonged blast plus two short blasts every two minutes. Explanation: Sound signals let other boaters know where you are located during periods of restricted visibility, such as extreme fog. If you hear the fog signal of a vessel you cannot see, slow to a minimum speed until you are sure there is not a risk of collision. One prolonged blast plus two short blasts at intervals of not more than two minutes is the signal used by sailing vessels.
One prolonged blast plus two short blasts every two minutes. Explanation: Sound signals let other boaters know where you are located during periods of restricted visibility, such as extreme fog. If you hear the fog signal of a vessel you cannot see, slow to a minimum speed until you are sure there is not a risk of collision. One prolonged blast plus two short blasts at intervals of not more than two minutes is the signal used by sailing vessels.