{"id":2629,"date":"2018-01-18T10:29:50","date_gmt":"2018-01-18T10:29:50","guid":{"rendered":"http:\/\/localhost:3000\/?p=2629"},"modified":"2022-01-31T07:11:27","modified_gmt":"2022-01-31T07:11:27","slug":"getting-fix-reality","status":"publish","type":"post","link":"https:\/\/abl-group.com\/abl\/all-media\/blog\/getting-fix-reality\/","title":{"rendered":"Getting a fix on reality"},"content":{"rendered":"

Electronic navigation, particularly with the advent of the Electronic Chart Display and Information System (ECDIS), has added more layers to the safe conduct of navigation. In order to deliver the promised enhanced safety of navigation, the Officer of the Watch (OOW) can be forgiven for abandoning many of the traditional chart work skills while adapting to the electronic chart. However, despite the move to electronic navigation, most of the traditional skills of yesterday remain just as valid today.<\/p>\n

It is impractical to make constant reference to the \u2018traditional\u2019 paper chart and simply trust in historical position fixing to give an accurate position. Dead reckoning (DR) ahead, at intervals not less than twice the distance to danger, should be the primary tool for keeping the vessel safe from grounding. Additionally, monitoring visual bearings (on those vessels fitted with a centreline pelorus) or radar parallel indexes, will provide \u2018real-time\u2019 precise track control. However, in the absence of any visual bearings or radar parallel indexes, the charted fix and an up-to-date DR position will provide \u2018near-real-time\u2019 track control to keep the vessel safe from grounding.<\/p>\n

Where not to be<\/h3>\n

It is fascinating that in the modern era, we know with absolute precision where a vessel grounded, courtesy of Global Navigation Satellite Systems. This means that, in the event of a grounding, the error was not so much failing to know where the vessel was, but failing to know where the vessel should not have been.<\/p>\n

The task of navigation remains a vital component of situational awareness, which means \u2018being able to identify, process and comprehend what is happening around you, where you are and where you are going\u2019. In effect, you either have situational awareness or you do not. It is not something lost if you never had it in the first place!<\/p>\n

Safe water and the no go line<\/h3>\n

In reality, the planned track is simply a \u2018datum\u2019 within the boundaries of the safe water limits defined by the \u2018No-Go\u2019 line that allows the navigator to keep the ship safe from grounding. This is like driving a vehicle along the road, where the kerb marks the \u2018No-Go\u2019 line and the driver maintains a safe distance and uses the white centre line or lane markers as reference points to maintain a safe position. (See Figure 1).<\/p>\n

Looking ahead<\/h3>\n

Another similarity with the road vehicle is the method used to drive smoothly, by looking ahead and scanning all round to predict where to place the vehicle on the road. The driver does not rely on looking down through the floor-pan (the shipboard equivalent would be real\u00adtime position monitoring by visual bearing or parallel index) or simply using the rear-view mirror (calculating based on historical position\u00a0fixing) to determine where the vehicle is heading, as this would result in erratic driving and be catastrophic. The driver looks ahead and uses constant feedback to determine where to point the vehicle. (See Figure 2.)<\/p>\n

Modern electronic navigation systems provide this function by giving a continuous vector of a pre-determined length\/time based on GNSS positioning. Additionally, ECDIS can provide a vessel-shaped predictor for monitoring the rate of turn when altering course. So to continue the analogy:<\/p>\n