WATCHOUT Do your layers line up?

01 Jun 2021 The Navigator

'Fusing' information from other input onto the ECDIS or radar display using an Integrated Navigation System (INS) can greatly assist the Officer of the Watch (OOW) – but it can also seriously hinder the safety of navigation if not managed properly. Here, the UK P&I Club takes a look at how bad management can occur, what it means and how to avoid it

If layers of information projected onto the on board INS do not synchronise, this can result in serious navigational and collision avoidance errors, which the operator may not always notice.

Lack of synchronisation can be caused by various factors:

  • Operator error due to not being properly familiar with the equipment provided
  • GPS/GNSS accuracy in relation to the visual or radar fix accuracy
  • Different speeds and courses from log input, as opposed to GPS track
  • AIS target time delay in relation to the radar echo
  • Lack of identification of radar targets

The loss prevention risk assessors of the UK P&I Club come across all of these errors at times. So how can they be avoided?

  • It is very important that the OOW is totally familiar with the equipment in use, as well as the INS of the particular vessel, and has been trained and pre-qualified on that system.
  • The system must be set to accurately reflect the track of the vessel at all times using speed over the ground and accurate position information. Avoid total reliance on GPS/GNSS. Use radar and visual fixes on ECDIS to ensure that the position of the vessel is properly monitored at all times.
  • Radar layering should be accurately aligned to the Electronic Navigational Chart (ENC). Any layering slip may indicate that position accuracy has been compromised. Make sure this is monitored at all times, especially in confined waters and in pilotage. In these situations, monitoring by all available means is even more vital in our estimation.
  • AIS and ARPA information layers must be used with caution. While AIS can give faster change of course and speed information, there are situations where linked target vectors can disassociate on screen. It is important to check all systems carefully and keep a good visual lookout. Never totally rely on the electronic information to be accurate.
  • INS layers can be very useful – but there are times in confined waters where it may be more prudent to turn layering off on the ECDIS and use the ARPA and AIS information on separate systems instead. It is crucial to monitor all systems and use visual collision avoidance and visual fixing for additional safety. If possible, the navigational watch should be doubled in order to monitor this.