Under SOLAS Chapter V (Regulation 19.2.2.3) and IMO Resolution MSC.128(75), all commercial cargo vessels of 150 GT and upwards and all passenger ships must be fitted with an approved Bridge Navigational Watch Alarm System (BNWAS). The system monitors bridge watchkeeper presence through physical or passive motion acknowledgment, initiating an escalating series of audible alarms to back-up navigators and officer cabins should the Officer of the Watch (OOW) become incapacitated.
Engineering Overview & Table of Contents
- 1. Regulatory Standards: IMO MSC.128(75) & IEC 62616 Compliance
- 2. Operational Modes & 3-Stage Escalating Alarm Sequences
- 3. Passive Infrared (PIR) Motion Sensors & Reset Push-Buttons
- 4. Autopilot Heading Interlock & Automatic Activation Logic
- 5. Back-Up Officer Cabin Buzzers, Mess Rooms & General Alarm Ties
- 6. Statutory Class Certification Across UAE Ports
1. Regulatory Standards: IMO MSC.128(75) & IEC 62616 Compliance
Navigational casualties frequently stem from solo bridge watchkeeper fatigue or sudden medical emergencies during nocturnal watches. BNWAS enforces continuous vigilance through un-resettable dormant countdowns. Seanav delivers certified BNWAS Supply and Installation, BNWAS Sensor Replacement, BNWAS Configuration and Programming, and statutory BNWAS Functional Testing across Furuno (BR-500), JRC (JCX-151 / JCX-161), Danelec, Highlander, and Martek Marine suites.
2. Operational Modes & 3-Stage Escalating Alarm Sequences
BNWAS incorporates three mandatory operational modes: Automatic (activated whenever autopilot or track control is engaged), Manual ON (always active), and Manual OFF (permitted only while vessel is safely berthed in port). Timing sequence conforms to strict statutory stages:
Statutory BNWAS Staged Alarm Sequence:
- Dormant Period (Td = 3 to 12 minutes): Configured by the Master (standard 12 minutes). Visual indicator flashes on the bridge console for 15 seconds at the end of dormancy.
- Stage 1 Bridge Alarm (15 seconds after dormancy): Loud, distinct audible alarm sounds on the navigation bridge only. Frequency modulates between 75 dBA and 85 dBA.
- Stage 2 Back-Up Officer Alarm (15 seconds after Stage 1): Audible alarm sounds in the designated Back-Up Navigator’s cabin and Master’s stateroom.
- Stage 3 General Ship Alarm (90–180 seconds after Stage 2): Master alarm sounds across crew accommodation spaces, officer mess rooms, and public lounges to summon all certified deck officers.
3. Passive Infrared (PIR) Motion Sensors & Reset Push-Buttons
To prevent watchkeeper distraction, modern BNWAS units utilize dual-tech PIR and microwave motion detectors mounted across bridge wings and console areas:
- Motion Detection Angle & Range: Testing 360° ceiling-mounted and 110° wall-mounted PIR sensors; ensuring watchkeeper movement along radar and chart tables resets dormant timers without blind spots.
- Anti-Tampering Diagnostics: Verifying sensors detect physical masking (tape or cardboard) and generate sensor fault alerts.
- Illuminated Reset Push-Buttons: Inspecting waterproof IP67 reset buttons on bridge wings, chart table consoles, and ECDIS desks.
4. Autopilot Heading Interlock & Automatic Activation Logic
SOLAS dictates that whenever the vessel’s heading control system (Autopilot) is engaged, the BNWAS must automatically turn ON without manual override. Seanav verifies autopilot dry-contact relays, NMEA sentence triggers (RSA / HTR), and key-lock security switches preventing unauthorized deactivation.
5. Back-Up Officer Cabin Buzzers, Mess Rooms & General Alarm Ties
Downstream cabin buzzers must be loud enough to wake sleeping officers:
| Alarm Destination | Sound Standard | Engineering Maintenance Scope |
|---|---|---|
| Master Stateroom | ≥ 75 dBA at bedhead | Testing Stage 2 buzzer volume, mute button interlock, and duty officer selector switch. |
| Duty Officer Cabins (1st, 2nd, 3rd Mate) | ≥ 75 dBA at bedhead | Auditing multi-position selector switch on bridge console; ensuring only the active watch officer’s cabin sounds. |
| Dedicated 24V DC Reserve Power | ≥ 6 hours autonomous operation | Load testing internal battery backup; testing AC mains failure audio-visual trouble alarm. |
6. Statutory Class Certification Across UAE Ports
Seanav provides turnkey BNWAS inspections, motion sensor replacements, and Class survey documentation across Kandla, Mundra, Mumbai, JNPT, Cochin, Chennai, Paradip, and Visakhapatnam.
Schedule BNWAS Annual Inspection or Motion Sensor Overhaul
Read detailed watchkeeping safety guidelines on our Bridge Navigation & Watchkeeping Hub or book an engineering visit at any Indian Commercial Port.