Glossary Term
BNWAS
BNWAS (bridge navigational watch alarm system) monitors the activity of the officer of the watch and, if no reset is made within a set period, raises a staged alarm: first on the bridge, then to the master or back-up officer and further crew.
Its purpose is to detect a watchkeeper who is not active on the bridge, for example through incapacity or falling asleep, and to bring someone else to the bridge in time. IMO performance standards for the system are in Resolution MSC.128(75), adopted in 2002.
How the BNWAS alarm sequence works
Under MSC.128(75), the system runs through fixed stages when it is not reset:
| Stage | What happens |
|---|---|
| Dormant period | Adjustable between 3 and 12 minutes. The watchkeeper resets the system within this period. |
| Visual indication | At the end of the dormant period, a visual indication is given on the bridge. |
| First stage | If not reset within 15 seconds, an audible alarm sounds on the bridge. |
| Second stage | If still not reset after a further 15 seconds, a remote alarm sounds in the location of the back-up officer and/or the master. |
| Third stage | Normally 90 seconds after the second stage (extendable at installation to a maximum of 3 minutes on larger vessels), an alarm sounds in the locations of further crew able to take corrective action. On ships other than passenger ships, this stage may be omitted if the second-stage alarm sounds in all of those locations at once. |
A reset needs a single operator action, through reset buttons or other approved inputs that register the watchkeeper’s activity. Holding or jamming a reset control must not stop the alarm sequence. An optional emergency call function lets the officer of the watch activate the second-stage alarm immediately, followed by the third.
Operating modes
MSC.128(75) specifies Automatic, Manual ON and Manual OFF modes, with access to the mode selector and the dormant-period setting restricted to the master. IMO guidance MSC.1/Circ.1474 advises that the automatic operational mode, if available, should not be used. The rules on when the system must be running come from SOLAS, below, and the vessel’s procedures.
SOLAS requirement
SOLAS regulation V/19.2.2.3, added by Resolution MSC.282(86), requires a BNWAS on cargo ships of 150 GT and above and passenger ships irrespective of size constructed on or after 1 July 2011. The system has to be in operation whenever the ship is underway at sea.
Existing ships built on or after 1 July 2002 were brought in by tonnage, each group by the first survey after a set date:
- Passenger ships and cargo ships of 3,000 GT and above: after 1 July 2012.
- Cargo ships of 500 GT to below 3,000 GT: after 1 July 2013.
- Cargo ships of 150 GT to below 500 GT: after 1 July 2014.
Resolution MSC.350(92) later set separate deadlines for ships built before 1 July 2002: the first survey after 1 January 2016, 2017 and 2018 respectively for the same three groups. Whether and how the requirement applies to a particular yacht depends on her size, use and flag, and on the yacht code she is certified to.
BNWAS on a yacht bridge
A BNWAS is only as useful as its layout. MSC.128(75) limits reset facilities to bridge positions that provide a proper lookout, and reset points need to be within reach of the positions where the watch is actually kept, and the remote alarms need to reach the cabins or spaces where the master and back-up officers are. When a bridge console is rebuilt or crew cabins are rearranged during a refit, the reset positions and alarm locations are worth reviewing with the flag or class surveyor, so that the system still meets MSC.128(75) and the vessel’s procedures. Integration with other bridge systems, such as the voyage data recorder or autopilot, follows the manufacturer’s documentation.
FAQ
What does BNWAS stand for?
Bridge navigational watch alarm system.
What is BNWAS on a ship?
A watch alarm that the officer of the watch resets at intervals of 3 to 12 minutes. If no reset is made, it alarms on the bridge first and then calls the master or back-up officer, and further crew.
Can BNWAS be switched off?
The system has a Manual OFF mode, with access restricted to the master. Where SOLAS V/19.2.2.3 applies, the BNWAS must be in operation whenever the ship is underway at sea; when it may be in Manual OFF is set by the flag rules and the vessel’s procedures.
What is the BNWAS dormant period?
The time, adjustable between 3 and 12 minutes, within which the watchkeeper must reset the system before the alarm sequence starts.
Is BNWAS required on yachts?
SOLAS requires it on cargo ships of 150 GT and above and on all passenger ships, with phased dates for existing ships. How that applies to a yacht depends on her tonnage, use and flag, and the yacht code she is certified to.