BNWAS Bridge Watch Alarm System: SOLAS V/19 & MSC.128(75) Guide

Single watchkeeper operations at night and during long ocean passages create severe risks of acute fatigue, microsleep, and sudden physical incapacitation. Under SOLAS Chapter V Regulation 19.2.2.3, all cargo ships of 150 gross tonnage and upwards and all passenger ships irrespective of size must be fitted with an approved Bridge Navigational Watch Alarm System (BNWAS).

The purpose of the system is strictly defined by IMO Resolution MSC.128(75): to monitor bridge activity and detect operator disability which could lead to marine casualties. The system enforces periodic confirmation of alertness from the Officer of the Watch (OOW); if the officer fails to acknowledge the system within a preset dormant period, an escalating series of visual and audible alarms alerts first the bridge, then the Master and backup officers, and ultimately the entire crew.

The core architecture of BNWAS relies on an unyielding, progressive timing cycle designed to awaken an inattentive officer or summon backup before the vessel runs into danger:

Key-Switch Security & Access Control: Under paragraph 4.2.2 of Resolution MSC.128(75), the means of selecting operational modes and the duration of the dormant period (Td) must be protected by security access controls (a physical key-switch held exclusively by the Master or a password-protected PIN). Leaving the physical key inserted in the BNWAS unit on the bridge is a frequent PSC observation.

Resolution MSC.128(75) originally provided three operational modes: Automatic, Manual ON, and Manual OFF. However, real-world casualty investigations revealed a fatal flaw in the Automatic mode:

The Danger of Automatic Mode: In Automatic mode, the BNWAS is connected to the autopilot or track control system, deactivating whenever hand steering is engaged. Several high-profile groundings occurred because the helmsman was dismissed to duties on deck while the OOW took manual steering, and subsequently fell asleep without the BNWAS active. Consequently, in MSC.1/Circ.1474, the IMO strongly recommended that BNWAS operational mode selection should remain in Manual ON whenever the ship is underway at sea.

The placement and mechanism of BNWAS reset devices must facilitate active watchkeeping without encouraging laziness or mechanical bypasses:

• Reset Button Locations: Push-buttons must be fitted at key conning positions within the wheelhouse, at the chart table, and on both bridge wings (MSC.128(75) § 4.1.1). Reset devices must be accessible only from areas of the bridge providing a proper lookout.
• Bridge Console Integration: Interfaced equipment (such as adjusting radar gain, interacting with ECDIS route menus, or pressing autopilot heading confirmation) may generate valid reset inputs if approved by the Administration.
• Passive Infrared (PIR) Motion Sensors: Where PIR sensors are fitted, they must be calibrated to detect natural watchkeeper movement across the wheelhouse while avoiding blind spots or spurious resets caused by heater blowers or sun glare.
• Prohibition of Mechanical Bypasses: Using weighted pendulums, desk fans, or taped-down switches to create false resets violates SOLAS V/19 and will result in immediate PSC detention under ISM Code safety management deficiencies.
• Emergency Call Button: A dedicated emergency call facility must be positioned on the centre conning console, enabling the OOW to immediately sound Stage 2/3 backup alarms if threatened by unauthorized boarders, medical collapse, or extreme navigational hazards.

Port State Control inspectors test BNWAS operational readiness under Tokyo MOU, Paris MoU, and USCG deficiency code 10127 (BNWAS):

• Full Operational Staging Test: Inspectors will request the OOW to arm the BNWAS, allow the dormant period to lapse, and verify that Stage 1 visual flashing occurs, followed 15s later by the bridge audible tone, and 15s later by the remote Master/officer cabin alarm.
• Cabin Buzzer Audibility: Verify that the alarm buzzer in the Master's and Chief Officer's cabins produces an audible sound level of >= 75 dB(A) over the noise of running cabin air conditioning or ventilation blowers.
• Bridge Wing Button Weatherproofing: Bridge wing reset buttons must maintain watertight integrity (IP56 minimum) and operate smoothly in freezing or wet conditions.
• VDR Interfacing (Res. MSC.333(90)): Confirm that BNWAS mode changes, reset pulses, and alarm transfers are logged in the VDR and verified during the annual VDR Performance Test.
• Power Supply & Battery Backup: Verify that failure of the main 220V/110V bridge power supply automatically trips to 24V DC emergency power or dedicated UPS battery with audible bridge power-loss notification.