Types of Alarm Signals on a Vessel

Updated July 19, 2017

Though travelling in a seagoing vessel can be pleasurable experience, the ocean is rife with peril. Operators of vessels provide safeguards to protect their passengers. In addition to lifeboats and other survival equipment, vessel operators use sound alarms and signals to warn passengers. Operators transporting large numbers of personnel prepare for emergencies.

Ships Whistle and Bell

U.S. laws require that ship sound systems meet requirements for volume and location. Essentially, the government ensures that the alarms are loud enough and in enough locations for everyone to hear them. The ship has two sound elements: the ship's general alarm bell, which makes a ringing sound, and the ships whistle, which is literally a foghorn.

The sound elements are classified as either prolonged blasts or short blasts. A short blast has a duration of one second, while a prolonged or long blast has a duration of four to six seconds. A long blast on the ship's bell consists of continuous ringing.

Fog and Collision

When fog limits visibility on the ocean, the ship's operators cannot see other vessels. The ship's operators signal their presence with the ship's whistle, more commonly known as a foghorn. The sound warning consists of one prolonged blast.

Additional sound signals indicate the direction the vessel will turn (in relation to its own direction). One short blast signals a right turn, and two short blasts signal a left turn. Three short blasts signal that the vessel will reverse direction. Five short blasts indicate that the operator either cannot control the ship's course or does not understand the sound signals of another vessel.


The personnel aboard ship are responsible for extinguishing fires and responding to emergencies. The sound signal alerting the crew of fire consists of 10 seconds of ringing of the alarm bell followed by 10 seconds of the ship's whistle. Afterward, the vessel operator directs the crew to respond to the emergency and provides any additional information over the public address system.

Abandon Ship

If the crew cannot control the fire or emergency, the vessel operator will sound the signal to abandon ship: six or more short blasts, followed by one longer blast sounded simultaneously on the ship's whistle and general alarm. In response, crew and passengers will report to assigned lifeboats and depart as directed.

Person Falling Overboard

Oceangoing vessels may carry thousands of passengers and accommodations. If one person falls overboard, the entire crew participates in the search for the victim. Locating one man overboard is difficult due to the vastness of the ocean. A single person who witnesses the accident should yell "Man overboard!" and notify the ship operator. A sound signal alerts the entire crew, who must aid in locating the individual in the water. Whoever locates the overboard member throws a life ring or other flotation device and points to inform the crew. The sound signal for man overboard consists of three prolonged blasts sounded simultaneously on the ship's whistle and alarm bell.

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About the Author

Miriam Breeze, a freelance writer since 2009, is a 12-year Marine Corps veteran and was a merchant mariner for five years. She specializes in health care topics and has published articles on and She has a Bachelor of Science in nursing from National University and a California registered nursing license.