BNWAS: Bridge Navigation Watch and Alarm System

  • Arya Kale 
  • 5 min read

What is BNWAS?

BNWAS stands for Bridge Navigation Watch and Alarm System. It is an instrument which is used to alert other officers that something has happened to OOW (Officer on watch) and he is incapable to perform his duties or he is not present on bridge at that time leading to a dangerous situation if being unattended to.


Here you can see that a keyhole is present to turn ON/OFF the system because only authorized officers are permitted to do so and if done, they must log in logbook stating time and proper reasons.

What are the three modes of BNWAS?

The alarm system has three modes:

Manual OFF

This indicates that the alarm is in OFF mode completely. This is ONLY put on when the ship is in dry-dock.

Manual ON

This indicates that the system is ON and must be reset within fixed interval.


In this mode the system resets itself when autopilot is engaged or any movement is detected by motion sensors /alterations to ECDIS or compass heading is made. This helps to retain focus of the navigator when maneuvering in limited waters.

What is Navigational Watch keeping?

OOW on his navigational watch
OOW on his navigational watch

When an officer is given responsibility of navigation of ship when he is on bridge, he is doing navigational watch keeping and now he is called OOW (Officer on Watch) for that time. His responsibilities include looking out for other vessels or any floating station and analyzing if that impedes the safe navigation of his own vessel. If it does then he is required to take action to avoid collision complying with COLREGS (International Regulations for preventing collision at sea).

Performing navigational watch

  •    The OOW must keep the watch on bridge and in no conditions shall leave the bridge until properly relieved by the next OOW.
  •    He will continue to be responsible for the safe navigation, even if captain is present on the bridge, until informed specifically that the captain has taken the responsibility and that is mutually understood.
  •    The OOW shall not be assigned or carry out duties which interferes with the safe navigation of the vessel.
  •    OOW shall know the handling characteristics of his own ship including the stopping distance and also keep in mind that different ships have different distance.
  •    The movements and activities observed during the watch must be recorded properly.
  •    The OOW shall notify the Captain immediately if restricted visibility is expected/ bad weather, increased traffic, any failure of navigational equipment/ machinery or if OOW feels that the presence of Captain is required to carry out the activities which contribute to the safe navigation of the vessel.

What are the regulations for BNWAS in SOLAS chapter V regulation 19 States?

  1. Merchant marine ships constructed on or after 1 July 2011 with a gross tonnage of 150 GRT and greater or any sized passenger ships.
  2. Cruise ships of any size constructed before 1 July 2011, not later than the    first survey after 1 July 2012.
  3. Cargo ships of 3,000 GRT and more constructed before 1 July 2011, not later than the first survey after 1 July 2012.
  4. Cargo ships of 500GRT till 3,000 GRT made before 1 July 2011, not later than the primary safety survey after 1 July 2013.
  5. Cargo ships of 150 GRT to 500 GRT constructed before 1 July 2011, not later than the primary survey after 1 July 2014.
  6. A BNWAS installed before 1 July 2011 may be exempted from compliance with the standards of the organization, at the discretion of the Administration.

Alarms and Indication

There are various stages of the Navigational Alarm system before it is sounded ship-wide alerting everyone on board.

Signaling light

When the BNWAS is activated, it has a fixed time period known as dormant period which is between 3-12 min. After the time is up, only then the alarm system is activated and OOW needs to “Silence” it. This procedure is known as “acknowledge the alarm”

  1. First stage: When the time is up, a visual indication is given consisting of flashing lights. This is an indication to acknowledge the alarm if OOW is operating nearby. If the flashing indication is not acknowledged within 15 seconds then audible alarm is sounded.
  2. Second stage: If that audible alarm is also not acknowledged then another alarm is sounded on bridge as well as in the Captain’s cabin whose sound is not identical to first one and is a bit louder than first stage alarm.
  3. Third stage: When the second stage alarm is not acknowledged in 90s then LOUD alarm is sounded all over the ship in every cabin and premises to alert all crew and indicate emergency.

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