CHIRP annual digest 2016 6th

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CHIRP Maritime passage plan approved by the Master (and clear to see on ECDIS) showed the course passing directly over the Nab Tower, which is clearly marked on the chart. Article. 33 Advisory Board Insight – Manoeuvring Issues in a Seaway A number of reports have reached CHIRP that have been so similar in their outlines that the suspicion is that watch officers are reaching conclusions about the circumstances that have been wrong and have resulted in closer encounters than would normally be considered accept - able, hence the scenarios finding their way to the CHIRP Marine Advisory Board. All such incidents are followed up and usually explanations are provided that then reveal viewpoints of the different parties. Sometimes this requires further clarifica tion but usually a number of conclusions can be reached at this relatively early stage. The number of reports received that display similar strategies however has prompted this article, in the hope that lessons may be learned by as wide an audience as possible. Some typical scenarios are: ■ Slow moving, usually very large and encumbered vessels being overtaken by faster, often similarly sized vessels; ■ As above but further encumbered by draught restric - tions and routing constraints; ■ Vessels of any size being overtaken by others of any size but being exposed to potential collision by the lack of appropriate action by the overtaking vessel; ■ Multiple vessel situations where overtaking and/or crossing vessels take inappropriate actions; and ■ Manoeuvres that pass too close to the other vessel. CHIRP Suggests This is a good example of why some ports have com - pulsory pilotage and shows the benefits of agreeing the passage plan between the pilot and the Master. For more information on ECDIS near misses please read CHIRP Maritime FEEDBACK 44. There was an apparent failure of the Safety Management System and its implementation on board. Every passage plan should be checked, agreed by the Master and then signed off by all of the navigation officers. In this case this clearly did not happen. The above article was published in MFB45 The link between all of the above is the development from a normal and relatively harmless situation to one that has become critical, which often requires action to avoid collision of not only the give way vessel but also that which is required initially to stand on. The scenarios that are described below are fictitious but are built on real reports. The situations are deliberately anonymised but it is hoped will be sufficiently familiar to mariners to enable them to apply the principles discussed to their own situations. Figure 1 is included to assist in the description. It is not to scale and is completely fictitious whilst representing reported events. The shaded areas depicted are the manoeuvring domains of the vessels, a concept that is explained later in the article. 39
-CHIRP Annual Digest 2016 Scenario 1: Overtaking Vessel A – a VLCC or Cape Size bulk carrier proceeding at around 12 knots in or approaching a routing system and/or a deep draught restricted channel; being overtaken by Vessel B – a medium sized or large container vessel proceeding at 20 knots overtaking Vessel A. The large differential between the two vessels’ speeds means that this scenario can develop very quickly. Besides being the stand on vessel the large vessel A is encumbered by its speed, its draught and the need to maintain sufficient under-keel clearance. Its large displace - ment also causes a sizeable delay on any manoeuvring, especially since the ratio of engine power to displacement is likely to be much smaller in A than it is in B. The overtaking vessel could also be encumbered by draught although it is unlikely to be as critical as it is for A. It follows that apart from the right to stand on provided in Rule 13(a), A should not be relied upon to take rapid avoiding action. It is often reported that B makes an alteration of course to port to leave A on the starboard side. The two vessels then very quickly draw level but then they are often navigating in disconcertingly close proximity. The large differential of speed rapidly causes B to draw ahead but it is also possible that the two large hulls might be close enough to experience hydrodynamic interaction. It is suspected that this may be the reality where reports of “aggressive” actions by vessels in this situation have been submitted. Interaction can become dangerous in that the effect of the rudder is increasingly nullified and can ultimately be lost completely with consequential loss of control, usually of the faster vessel, followed by the drawing together of the hulls into a collision. The ongoing situation however also presents problems as the overtaking vessel, which remains responsible for E D C WPA A ✗ ✔ B Figure 1: Situation involving multiple encounters 40
Page 1 and 2: CHIRP Maritime The Maritime Confide
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Page 73 and 74: The sponsors of this Annual Digest

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