Bridge Navigational Watch Alarm System (BNWAS)

The purpose of a bridge navigational watch alarm system (BNWAS) is to monitor bridge activity and detect operator disability which could lead to marine accidents. The system monitors the awareness of the Officer of the Watch (OOW) and automatically alerts the Master or another qualified OOW if for any reason the OOW becomes incapable of performing the OOW’s duties.

This purpose is achieved by a series of indications and alarms to alert first the OOW and, if he is not responding, then to alert the Master or another qualified OOW. Additionally, the BNWAS may provide the OOW with a means of calling for immediate assistance if required. The BNWAS should be operational whenever the ship’s heading or track control system is engaged unless inhibited by the Master.

Application dates

SOLAS Ch.V Reg.19 as amended by res. MSC.282(86), adopted on 2009-06-05, has introduced a carriage requirement for BNWAS as follows:

Cargo ships > 150 GT and all passenger ships constructed on or after 1 July 2011;
All Passenger ships constructed before 1 July 2011, first survey after 1 July 2012;
Cargo ships > 3000 GT constructed before 1 July 2011, first survey after 1 July 2012;
Cargo ships > 500 GT but < 3000 GT constructed before 1 July 2011, first survey after 1 July 2013; and
Cargo ships >150 GT but < 500 GT constructed before 1 July 2011, first survey after 1 July 2014.

The bridge navigational watch alarm system shall be in operation whenever the ship is underway at sea. A bridge navigational watch alarm system (BNWAS) installed prior to 1 July 2011 may subsequently be exempted from full compliance with the standards adopted by the Organization, at the discretion of the Administration.

Operational Modes:

Automatic (Automatically brought into operation whenever the ship’s heading or track control system is activated and inhibited when this system is not activated)

Manual ON (In operation constantly)
Manual OFF (Does not operate under any circumstances)

The requirement has the following main technical characteristics:

After the system has been activated no alarm for a period of 3 to 12 minutes.
After this period, the system initiates a visual alarm on the bridge
If not reset, within a period of 15 seconds an audible alarm on the bridge is activated (First Stage).
If not reset, within a period of 15 seconds from last audible bridge alarm, a second stage audible alarm is activated in the backup officer’s and/or Master’s location.
If not reset, a third stage alarm is activated in a remote location where other officers can take corrective action within 90 seconds from the initiation of second stage alarm.
In vessels other than passenger vessels the second and the third stage alarms may sound in all of the above location at the same time.
In larger vessels time delay between second and third alarm can be set up to a maximum of 3 minutes.

Visual indications

The visual indication initiated at the end of the dormant period should take the form of a flashing indication. Flashing indications should be visible from all operational positions on the bridge where the OOW may reasonably be expected to be stationed. The colour of the indication(s) should be chosen so as not to impair night vision and dimming facilities (although not to extinction) should be incorporated.

First stage bridge audible alarm

The first stage audible alarm which sounds on the bridge at the end of the visual indication period should have its own characteristic tone or modulation intended to alert, but not to startle, the OOW. This alarm should be audible from all operational positions on the bridge where the OOW may reasonably be expected to be stationed. This function may be engineered using one or more sounding devices. Tone/modulation characteristics and volume level should be select-able during commissioning of the system.

Second and third stage remote audible alarm

The remote audible alarm which sounds in the locations of the Master, officers and further crew members capable of taking corrective action at the end of the bridge audible alarm period, should be easily identifiable by its sound and should indicate urgency. The volume of this alarm should be sufficient for it to be heard throughout the locations above and to wake sleeping persons.

RESET Function

It should not be possible to initiate the reset function or cancel the audible alarm from a device not physically located in the bridge area providing proper lookout.
The reset function should, by a single operator action, cancel the visual indication and all audible alarms and initiate a further dormant period. If the reset function is activated before the end of the dormant period, the period should be re-initiated to run for its full duration from the time of the reset.
The single operation reset action must be in such a way that will ensure mental alertness of the OOW.
A continuous activation of any reset device should not prolong the dormant period or cause a suppression of the sequence of indications and alarms.

Emergency calls facility

Means may be provided on the bridge to immediately activate the second, and subsequently third, stage remote audible alarms by means of an “Emergency Call” push button or similar.

Accuracy : The alarm system should be capable of achieving the timings with an accuracy of 5% or 5 s, whichever is less, under all environmental conditions.

Malfunction: If a malfunction of, or power supply failure to, the BNWAS is detected, this should be indicated. Means shall be provided to allow the repeat of this indication on a central alarm panel if fitted.

All items of equipment forming part of the BNWAS should be tamper-proof so that no member of the crew may interfere with the system’s operation.

An example layout of BNWAS on ships

* RESOLUTION MSC.128(75) (adopted on 20 May 2002) – PERFORMANCE STANDARDS FOR A BRIDGE NAVIGATIONAL WATCH ALARM SYSTEM (BNWAS)