A Bridge Navigational Watch Alarm System (hereafter 'BNWAS') is to monitor bridge activity and detects disability of OOW (Officer Of the Watch), which could lead to marine accidents.
On June 5th, 2009 IMO in Resolution MSC.282 86th session decided that all new cargo ships over 150GT and all new passenger ships of any size constructed after July 1st, 2011 have to be equipped with a BNWAS.
Furthermore, all existing passenger ships and cargo vessels over 3,000GT have to be equipped with a BNWAS not later than the first special survey after July 1st, 2012 and all existing cargo ships over 500GT by the first survey after July 1st, 2013.
The final category of vessels, cargo ships over 150GT, will have to comply with the Resolution MSC.282 86th session by July 1st, 2014.
Existing BNWAS requires that a reset push button shall be pressed by OOW to confirm his presence on the bridge at every three to twelve minutes.
Ship's crew has complained that at some circumstances it may be difficult to share attention between resetting BNWAS and other bridge activities.
In reply to the complaint, IMO has allowed motion sensor to be used as resetting device.
The motion sensor detects movements on the bridge and subsequently sends reset signals directly to BNWAS automatically and as a result, crew can work uninterrupted.
But some of classification societies and flag authorities have a slightly different stance on motion sensor as a resetting method for BNWAS, since the motion sensor may trigger false reset signals caused by air-conditioning systems, objects moving on the bridge, especially sleep movement such as toss and turn of OOW which could extend incapable period of performing the OOW's duties.
This paper proposes a simple configuration of BNWAS, which consists of only three motion sensors associated with AND and OR logic gates.
Additionally, several consideration points are also proposed for safe implementation of motion sensor for BNWAS.
This study found that the proposed configuration which consists of three motion sensors is better for reducing risk over 60% against problem of false reset by slight sleep movement of OOW which may affect conventional BNWAS configuration.
The proposed configuration in this paper provides filtering of false reset signals and is simple to be implemented on existing vessels.
In addition, it can be easily installed even by ship's crew with a basic electrical knowledge.