What to check on a BNWAS.
1 models from Kelvin Hughes in BNWAS. Below: the full model list.
What this type is
The Bridge Navigational Watch Alarm System monitors whether the officer of the watch is present and active on the bridge, escalating through a defined alarm sequence if no activity is detected within a set interval. It is not a fatigue or competence monitor; it detects only physical inactivity at the console — no button press, no motion sensor trigger, no bridge equipment interaction within the timer window. SOLAS makes it mandatory precisely because incapacitation or falling asleep on watch has caused groundings that no other bridge system was designed to catch.
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Main components
- Reset points — dedicated buttons or motion sensors positioned around the bridge so the OOW can reset the timer from the normal watchkeeping positions.
- Timer/logic unit — runs the adjustable 3-12 minute inactivity interval and the alarm escalation sequence.
- Stage 1 alarm — visual/audible alert on the bridge itself, giving the OOW a short window to reset.
- Stage 2 alarm — extends the alert, often to a location the OOW would need to move to reset, so a genuinely present but preoccupied officer still resets it.
- Stage 3 backup alarm — sounds in the master's cabin and/or designated officer's cabin(s), and on some installations additional crew spaces, when stages 1 and 2 are not acknowledged.
Selection and sizing
The main selection variable is reset point layout, not the electronics — the points must cover every position the OOW legitimately works from (chart table, radar, bridge wings on vessels where wing watchkeeping is normal) so a genuinely attentive officer is never falsely alarmed for being at a different console. The backup alarm routing (which cabins, which public spaces) must match the vessel's actual watch and manning structure.
Regulations and class
SOLAS Chapter V, Regulation 19, requires BNWAS on all vessels of 150 gross tonnage and upward on international voyages, phased in by vessel type and build date. Performance standards are set out in IMO resolution MSC.128(75), covering the timer ranges, alarm stages and escalation timing. Class survey checks the fitted system carries type approval to this standard and that the alarm sequence and cabin routing match what was tested at commissioning.
Typical faults
- Reset button wedged or taped down — defeats the entire system while showing no fault, the single most common documented failure mode.
- Motion-sensor reset points triggered by routine bridge movement unrelated to actual watchkeeping, masking genuine inactivity.
- Stage 3 cabin alarm wiring not tested after a crew cabin reassignment, so the backup alert goes to an empty room.
- Timer interval left at a setting inappropriate for the vessel's operation, causing either alarm fatigue or too long a gap before escalation.
What to look for in a supplier
- Type approval to MSC.128(75) with the certificate matching the exact model installed.
- Reset point layout proposal based on the vessel's actual bridge arrangement, not a generic template.
- Backup alarm routing configurable to the vessel's manning and cabin layout.
- Commissioning test report confirming every stage and every cabin alarm was verified, not just stage 1.
Test BNWAS by letting it run through to stage 3 during commissioning and after any crew accommodation change — a system that has only ever been reset at stage 1 has never proven its backup alarm actually reaches anyone.