Dec 122010
 
Birthe Thres and Vasia

Top: Vasia, Bottom: Birthe Theresa

Hydrodynamic forces between ships traversing the Kiel Canal should be studied, says Germany’s Federal Bureau of Maritime Casualty Investigation. The report also highlights responsibility of pilots conducting vessels whose masters do not understand German and the role of Vessel Traffic System operators.

To cut to the chase, while the Cyprus-flagged tanker  Vasi was overtaking the Singapore-flagged Birthe Theresa in the relatively narrow and shallow canal, the latter suddenly picked up speed, went to port and contacted Vasi. For around seven minutes the two vessels continued stuck together until Birthe Theresa went to starboard and ran aground on the canal embankment.

Says the BSU report: “…when the overtaking manoeuvre was almost complete, i.e. the Vasi’s stern was abreast with the bow of the Birthe Theresa, the overtaken vessel developed a strong, inward turning yaw-moment, which is typical in this phase. This led to the Birthe Theresa yawing to port and heading for the overtaking Vasi.

Lateral distance decreased rapidly and the so-called ‘trapping phenomenon’ occurred. In this phase, it is no longer possible for the overtaking vessel to increase her speed, even if the rate of speed is set so that higher speeds must be possible. There is an absolute loss in propulsion. In contrast, the speed of the overtaken vessel steadily increases even if the engine is set to STOP. In extreme cases, the speed of the overtaken vessel can exceed that of the overtaking vessel. As was the case here and in most other cases, the affect of the interactive forces and moments leads to parallel contact between the vessels, which then may continue ‘in a packet’”.

image

Birthe Theresa unsticks and head for a grounding

It is far from the first such incident. The BSU report refers, to the fact that in the future more attention should be given to the risk posed by suction during overtaking manoeuvres on the narrow fairway of the river Elbe in the report on the collision between the Cosco Hamburg and the Nedlloyd Finland.

While there are recommendations, but no mandatory instructions, for safe passing distance the BSU expresses concern that given the increasing size of vessels approaching Hamburg through the restricted waterways there may not be enough knowledge about the effects of hydrodynamic forces.

Neither master spoke German and there were pilots on both vessels; therefore, the masters “had to rely on the agreements and actions of the pilots”.

Says the BSU: “Neither pilot met his obligation to advise his respective master in a manner that complies with the applicable regulations. Even without VHF radio, the situation could have been resolved by following the applicable regulations.

The pilot of the Birthe Theresa allowed the vessel to enter the canal traffic, even though he disturbed the right-of-way of the Vasi in doing so. Conversely, the pilot of the VASI intended to allow the Birthe Theresa right-of-way so that the otherwise forthcoming overtaking manoeuvre could be avoided. On the other hand, he recognised that his vessel was to some extent pressed for time in terms of reaching the Schwartenbek siding area and therefore accepted that he may need to exceed the maximum permissible speed limit for so-called low-speed vessels. Allowing the Birthe Theresa right-of-way and yet also reaching the Schwartenbek siding area on time could, at any event, only be successful if the Birthe Theresa would have picked up speed swiftly. The pilot of the Vasi ultimately felt compelled to overtake the Birthe Theresa when this did not happen. The pilot of MT Vasi initially dispensed with his right of way and later on attempted to reclaim it for the purpose of overtaking. However, the audio recordings do not register the Birthe Theresa agreeing with that… The audio recordings demonstrate the dangers associated with making arrangements, in this case between pilots, over VHF if they are not timely, and not objective”.

BSU also suggests that the accident might have been avoided of the VTS had been more proactive: “When both vessels contacted the VTS in short succession and reported their departure, the opportunity existed for the VTS to clarify exactly who should wait for who. At minimum, it should have informed each vessel about the other and their respective intentions. This could have contributed to the prevention of the accident.

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