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should not rely on AIS alone, andshould not use the AIS as an ex-cuse to slacken his lookout or re-sponsibility. This statementagrees fully with COLREGS re-quirements for good seamanshipand proper look-out.

The reader should also beaware that, in interpreting AISdata by ECDIS systems, the goodpractice is to use the target posi-tions only and not trust the SOG(Speed Over Ground) and COG(Course Over Ground) computedand sent by the target’s AIStransmitter. Those parametersare calculated separately usingthe Kalman algorithm, as is cus-tomary with ARPA systems.

Item 40 of the AIS guidelines

clearly state that ‘AIS informationmay be used to assist in collisionavoidance decision-making’.Totem says that the decision sup-port tools incorporated into itsECDIS are invaluable in this task.The tools provide the OOW witha recommended course of action,either the exact course change orthe exact speed change that isnecessary to avert a collision.This more methodical approachto decision-making – based onboth AIS and ARPA information –results in the right decision beingmade more of the time, says thecompany. The OEM adds that theTotem ECDIS is compliant bothwith IMO guidelines (particularlyitems 40.1, 41 and 43) and withthe COLREGS.

The value of Totem ECDIS’decision making capabilities inclose proximity situations wasdemonstrated in a real situationonboard a fast car carrier in theNorth Sea. The vessel was steam-ing on a course of 120°T at 15.7knots, with about a dozen targets(both AIS and ARPA) in closeproximity (Fig 1). The system ad-vised turning 18° to starboardand steer 140°T, in order to stay0.5 miles from all targets (Fig 2).By following this advisory, theOOW maintained a safe distancefrom the targets.

Decision support tools are al-ready used for other aspects ofnavigation, notably for ground-ing avoidance and route plan-ning. The adoption of ECDIS forcollision avoidance tools is a nat-ural progression. The view heldby some navigators – namely ‘weknow the rules of the road, wedon’t need the machine to tell uswhat to do’ – is still in evidence.But if everybody knows therules, then why do we have somany collisions?

AIS was formally in-troduced in 2001, yetthe use of AIS dataon board remains a

matter of some uncertainty. Be-cause the International Regula-tions for Preventing Collisions atSea (1972), more commonlyknown as COLREGS, predateAIS by almost three decades,they naturally make no refer-ence to AIS and only discussradar. Consequently, many o�-cers and Masters – erring on theside of caution – take the viewthat AIS information SHOULDNOT be used for collision avoid-ance.

This over-zealous interpreta-tion of the rules possibly stemsfrom marine academies and suchlike following the letter of thelaw rather than its spirit. Naviga-tion hardware supplier Totem isof the opinion that AIS informa-tion SHOULD be used for colli-sion avoidance.

Readers who are clued up ontheir COLREGS will quicklypoint out that reluctance to trustAIS is misguided, citing rule 7(a),which states ‘every vessel shalluse all available means appropri-ate’. But mariners are not sup-posed to be legal experts. Theyshould not be forced into a posi-tion where they have to considerall possible interpretations of therules foisted upon them.

In order to further under-stand this issue, one must goback to the guidelines originallyissued by IMO on the ‘ Use of AISin Collision Avoidance Situations ’in November 2001 (IMO ResA.917 (22)), which, incidentally,are set to be revised in 2014.

The guidelines state that ‘AISis an additional source of naviga-tional information’, and furtherthat ‘AIS can assist in tracking it[a detected ship] as a target’. Incombination with the COLREGSrequirement that the O�cer ofthe Watch (OOW) should use ‘allavailable means’, it can be con-cluded that IMO intended AIS tobe used for collision-avoidancepurposes.

However, a word of cautionshould be given: the guidelinesalso warn that the mariner

AIS

A collision ofinterpretations

Fig 1: (top) Thevessel is surroundedby targets

Fig 2: (bottom)By changing course,the ship maintaineda safe distance

AIS can play an invaluable role incollision avoidance, but mariners aresometimes unsure whether theyshould follow its advice

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