4.2 The difficulty of discerning navigation in spite of proper situational assessment:
The Heranger incident happened within a narrow channel, but a similar problem can easily be imagined at the entrance of a narrow channel. An outbound vessel can experience quite some difficulty in predicting the navigation of a vessel approaching the entrance of a narrow channel. Observing the manoeuvres of a vessel approaching the entrance of a narrow channel might not say much about whether said vessel is intending to enter or to simply pass by the entrance until the vessel is perhaps much too close to the entrance. Other discernible factors might not be of much help either. Depending on the side, the angle and place of origin from where the approaching vessel is coming, one and the same manoeuvre could be made to achieve various goals. Figures a, b & c below show an example of a starboard alteration made by an approaching vessel for different purposes. The outbound vessel may have a hard time settling on one conclusion among all the possibilities before the approaching vessel is much too close. This is perhaps why the nautical assessors’ advice in The Alexandra I, on the proper way to solve the hypothetical encounter between an outbound vessel and an approaching vessel bearing on her starboard bow (i.e. coming from the opposite side than the vessel in Fig. a, b and c), involved ascertaining the intentions of the approaching vessel from VTS and using VHF communication.
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Fig. a Vessel B altering to starboard to stop at the pilot boarding area
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Fig. b Vessel B altering to starboard to keep out of the way of vessel A
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Fig. c Vessel B altering to starboard to enter the narrow channel
Whenever a conclusion is reached about the navigation of another vessel, there are three possible outcomes. The conclusion can be correct, or it can be wrong in either of two ways. The decision could be a ‘false positive’ where one assumes that something is correct when it is not, or a ‘false negative’, meaning that a certain thing is deemed untrue when it is actually true.(1) Craig H. Allen, Farewell’s Rules of the Nautical Road, 2020, p. 180.Relying on the ability of vessels to predict each other’s navigation might be necessary, but it is also dangerous. As such, reliance on it should perhaps be kept to a minimum whenever possible.