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BNWAS and Anti-Collision Alert Systems

The Bridge Navigational Watch Alarm System verifies that the officer of the watch is genuinely present and alert, with an escalating alarm sequence up to the Master: mandatory since 2011 for cargo ships ≥150 GT, yet still often poorly understood in day-to-day operational use.

BNWASSOLAS V/19anti-collision alertwatchkeeping

Operational Explanation

The BNWAS (Bridge Navigational Watch Alarm System) is a device that monitors the presence and responsiveness of the officer of the watch on the bridge, distinct from collision-risk detection systems (ARPA, AIS) that instead monitor surrounding traffic. A BNWAS cycle begins with a dormant period (typically adjustable between 3 and 12 minutes), at the end of which the system requires an active reset by the officer; in the absence of a response, a progressive alarm sequence is triggered: first a visual/audible alarm on the bridge, then a remote alarm to backup officers or the Master.

Distinct but complementary, the task of detecting collision risk from surrounding traffic remains entrusted to ARPA systems and AIS-integrated surveillance, whose effectiveness in any case depends on the full vigilance of the officer of the watch that the BNWAS is designed to verify.

Regulatory Reference

SOLAS Chapter V, Regulation 19 makes the BNWAS mandatory for passenger ships and for cargo ships of gross tonnage 150 and above; it must be operational whenever the ship is under way. Performance standards are set out in IMO Resolution MSC.128(75), which requires automatic activation when the ship is under way or with the autopilot engaged.

Scope of Application

All ships subject to the SOLAS V/19 requirement, with the officer of the watch responsible for correctly responding to the system's prompts and the command responsible for verifying its correct configuration and periodic functioning.

Procedure / How to Complete It

  1. Verify that the BNWAS is active and correctly configured whenever the ship is under way or with the autopilot engaged.
  2. Respond to the system's reset prompts within the configured dormant period, without systematic delays that would indicate purely mechanical handling of the device.
  3. Carry out the periodic end-to-end test: timer prompt, bridge alarm, remote alarm, and cancellation, verifying every stage of the sequence.
  4. Simulate a main power failure during the test to verify that the system remains operational and generates the required alarm in the event of loss of main power.
  5. Do not disable or bypass the BNWAS for operational convenience, even in conditions of reduced traffic or calm seas.

Practical Example

Example periodic test: the officer of the watch carries out the BNWAS end-to-end test, verifying the timer prompt after the configured interval, activation of the bridge alarm in the absence of a response, escalation to the remote alarm towards the Master's cabin, and correct cancellation after the reset, recording the outcome in the bridge log.

Real Cases

The BNWAS originates precisely from the analysis of incidents in which the officer of the watch was found to be absent from the bridge or not alert (through illness, involuntary sleep or unauthorised absence) without any mechanism detecting it in time: the escalating alarm sequence up to the Master is specifically designed to intercept this scenario before it develops into a navigational incident.

Common Mistakes Mistake Library

MistakeConsequenceHow to avoid it
BNWAS treated as a mechanical formality, with automatic or near-automatic resets without genuine verification of alertnessThe system loses its function of genuinely verifying the officer's active presenceRespond to prompts as a conscious check, not as an automatic and distracted gesture
Periodic test limited to checking the timer prompt alone, without testing the full escalation sequenceMalfunction of the remote alarm not detected until a real emergencyAlways carry out the full end-to-end test: timer, bridge alarm, remote alarm, cancellation
Dormant period configured at the maximum allowed value to reduce the frequency of promptsA wider detection window in the event of genuine absence or incapacity of the officer of the watchConfigure the dormant period according to the real risk profile of the navigation, not merely to minimise disturbance

PSC Observations

PSCOs verify that the BNWAS is installed, functioning and correctly configured for automatic activation while under way; they may request a demonstration of the end-to-end alarm sequence test during the inspection.

Operational Tips

Checklist

FAQ

Which ships must have a mandatory BNWAS?
Passenger ships and cargo ships of gross tonnage 150 and above, under SOLAS Chapter V, Regulation 19; it must be operational whenever the ship is under way.
Does the BNWAS replace collision-risk detection systems such as ARPA?
No: the BNWAS verifies the presence and alertness of the officer of the watch, while ARPA and AIS-integrated surveillance detect collision risk from surrounding traffic; they are complementary, not substitute, systems.
What must a BNWAS end-to-end test include?
Verification of the timer prompt, the bridge alarm, the remote alarm to backup officers or the Master, and correct cancellation after the reset, following the complete sequence provided for by the system.
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Related Topics

WatchkeepingBridge Resource Management