BNWAS exists for one grim scenario: the officer of the watch incapacitated or absent, and a vessel sailing on with nobody watching. The system’s logic is a study in designing against human factors.
The escalation ladder
A dormant-period timer (settable per regulation, typically minutes) runs continuously; activity on the bridge resets it — motion detectors, deliberate reset pushes, or interactions with navigation equipment, per the installation’s approved reset-source list. Expiry starts the ladder: first a visual indication on the bridge, then an audible bridge alarm, then — the point of the whole system — remote alarms in the master’s and officers’ cabins, and finally general escalation to further crew stations. Each stage’s delay is regulation-bounded; the design intent is that somebody physically arrives.
Engineering notes from retrofits: reset sources must reflect genuine watchkeeping (a motion sensor watching a chair defeats the purpose — placement is an ergonomics exercise); the emergency-call function (immediate escalation button) wants wiring independence that survives the scenarios BNWAS exists for; and power supervision matters — the system that guards the watch must announce its own failure loudly.
Integration temptation deserves caution: BNWAS talking to the central alarm system for logging is good; making its escalation depend on shared infrastructure is exactly backwards. Standalone integrity first, integration as garnish.
FAQ
Who may adjust the dormant period? Master-controlled per the rules, with settings protected — an “adjusted” BNWAS found at survey is a finding with teeth.
Retrofit effort on an older vessel? Modest hardware, meaningful cabling (cabin alarm circuits), and approval paperwork — plan it with a drydock or lay-up rather than alongside a working schedule.
Zone Otomasyon installs and certifies bridge safety systems as part of vessel electrical retrofits. Vessel systems.