Maritime sound signals

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Here are the sound signal rules to be followed by vessels in restricted visibility:
A power-driven vessel underway must sound one prolonged blast every two minutes.
A power-driven vessel underway but stopped and making no way through the water must sound two prolonged blasts every 2 minutes with an interval of about 2 seconds between them.
A vessel not under command; a vessel restricted in her ability to maneuver, whether underway or at anchor; a vessel constrained by her draft; a sailing vessel; a vessel engaged in fishing, whether underway or at anchor; or a vessel engaged in towing or pushing another vessel must sound one prolonged blast plus two short blasts every two minutes.
A vessel at anchor must ring the bell rapidly for 5 seconds every one minute.
A vessel at anchor of 100 meters or more in length is required to ring the bell rapidly for 5 seconds every one minute, and immediately after the ringing of the bell to sound the gong for 5 seconds in the aft part of the vessel.