BNWAS (Bridge Navigational Watch Alarm)

What sets BNWAS apart

A Bridge Navigational Watch Alarm System does not monitor the ship's course or track; it monitors the presence of an alert human on the bridge. It works from an assumption that a watchkeeper interacts with bridge controls, resets buttons or motion sensors on a regular basis, and treats a long enough silence as a sign the officer of the watch may be incapacitated, asleep, or has left the bridge. That distinguishes it from an autopilot off-course alarm or a track control alarm, which detect a navigational deviation rather than the absence of the watchkeeper who would normally have corrected it.

Main components

Motion or activity sensors

Passive infrared sensors, or reset buttons distributed around the bridge, that register watchkeeper presence and activity.

Dormant period timer

A configurable interval, commonly adjustable between around 3 and 12 minutes, after which the system moves from dormant to first-stage alarm if no activity has been registered.

First and second stage alarm units

Audible and visual alarms on the bridge itself, followed if unacknowledged by alarms extended to the master's or backup officer's cabin and other crew locations defined in the ship's procedures.

Central control unit

Manages the escalation logic, interfaces with the ship's alarm system, and typically logs alarm events for review.

Selection and configuration

Selection is less about competing designs and more about correct configuration: dormant period length, which sensors count as valid activity, and the escalation chain of cabins and locations alerted at each stage must all be set to match the ship's actual watchkeeping arrangements and manning. A system configured with too short a dormant period generates nuisance alarms that crews learn to silence reflexively, which defeats the entire purpose.

Regulations and class

IMO adopted BNWAS as mandatory under SOLAS Chapter V, Regulation 19, with a phased implementation completed by 2011 across new and, on a schedule, existing ships above defined size thresholds. The regulation sets the minimum functional requirements — dormant period range, escalation stages, and backup alerting — while allowing flag states and class societies to specify installation and testing detail through type approval and survey.

Typical faults

• Dormant period set too long — undermines the safety intent, since a watchkeeper could be incapacitated for an extended period before any alarm triggers.
• Reset button used reflexively without genuine watchkeeping — an officer can silence the system out of habit while not actually maintaining a proper lookout, a training and procedure issue rather than an equipment fault.
• Escalation chain not tested to actual cabins — the second-stage alarm is wired to a cabin no longer occupied by the backup officer after a crew change, leaving no effective backup.
• Motion sensor blocked or miscounted — a sensor obstructed by equipment or paperwork stops registering activity, causing nuisance first-stage alarms even with an alert watch present.

What to look for in a supplier

• Type approval confirming compliance with the applicable performance standard for BNWAS.
• Flexible sensor and reset button placement options matching the specific bridge layout.
• Straightforward reconfiguration of dormant period and escalation chain without a service engineer visit for routine crew changes.
• Alarm logging that supports audit and, where relevant, incident investigation.

Review the escalation chain contact list at every crew change, not just at the annual survey — a BNWAS alarm routed to an empty cabin gives a false sense of backup coverage.