Why ECDIS cannot or should not be used for collision avoidance?

ECDIS has made it much easier for the navigator to safely navigate the ships. But that is only true if the ECDIS is used in a correct way and if it is used to its potential.

ECDIS can surely help in collision avoidance and it must be used for collision avoidance but not as a stand-alone equipment.

ECDIS complements other equipments on the bridge during collision avoidance. But if it is used without looking at the radars and visual look out, it will lead to dangerous consequences.

The positive thing about using ECDIS during collision avoidance is that if we have to take avoiding action, we would know at all the times where the sea room is. This, of course, is applicable if we have entered the correct safety setting in the ECDIS.  

It also gives the instant positions of the targets on the chart. This helps the navigators to have a proactive approach.

For example, If the target is proceeding in the TSS we can easily take into consideration the possible future movements of the target as per the general traffic flow of the TSS.

But the negative thing about using ECDIS as collision avoidance is that the target positions may not be correct in the ECDIS as it displays the target from the AIS which may not be giving correct positions of the targets.

While identifying the targets by comparing the visual bearings of the target with the ECDIS can also lead to confusions in the case of multiple targets at close proximity. As the AIS positions of the targets may be offset by few cables or miles, the visual bearing may not match with the accurate targets.  

Also not all the targets will be plotted on the ECDIS. For example, fishing boats that do not have AIS will not be plotted on the ECDIS. Or if the target has its AIS switched off or AIS is not working, this can lead to confusions.

So when a target is identified, we may use ECDIS for deciding an action or for deciding if there is sufficient sea room available for the intended action but we must identify the targets by other reliable means like radar and visual look out.

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