S1/2007M Collisions with harbour structures used by passenger vessels
As vessel sizes have increased, the safety margins in harbour manoeuvring have decreased. There have been several collisions involving ro-ro passenger vessels and harbour structures. This safety study describes collisions in passenger ferry harbours and the most important passenger harbours in Finland, their pier structures, and the passenger and car traffic on the harbour areas. Minor bumps against port fenders, which may result in fender damages, occur often in harbours. This safety study does not deal with these cases.
The risks related to collision accidents are evaluated from the perspective of the harbour. A vessel colliding with the harbour structures due to human error, strong winds, or equipment failure can cause danger to people in the harbour. Modern ro-ro vessels usually have a full-width aft in order to meet the requirements of current stability regulations. With vertical sides at the midship, the curved bow is the only part that can hit the passenger bridges and other structures inside the edge of the pier in a collision.
Equipment failure can also affect the risk level of the operation indirectly. For example, in the event of an operating error in the cargo door, the vessel may be docked in a way deviating from the usual method to enable unloading the cargo. This kind of rare operation may increase the risk of collision due to the lack of routine and difficulties in estimating the effects of the circumstances.
This safety study evaluates the risk caused to the people and vehicles in the harbour area and to the harbour structures by a vessel colliding with the pier. Possible damages caused by breaking mooring rope lashings of a docked vessel are also discussed.
Factors that affect passenger safety in harbours include the location of the passenger and car flows on the harbour areas, and their timing in relation to the vessel traffic. For some harbours, the risk level is increased by the location of passenger bridges close to the pier line, the location of the car lanes close to the moorings, or passenger flows on passenger bridges and car routes simultaneously with vessel manoeuvrings in the next quay space, due to scheduling.
The number of collisions can be reduced, and in the event of a collision, the amount of material damage can be minimised and personal safety improved by implementing and using the pier structures correctly, defining operating limits, and by properly planning the harbour manoeuvring operations.
The effect of environmental factors particularly on the operation of ro-ro vessels in the harbour area is significant. The large lateral surface of these vessels limits their operations in high winds. Often weather conditions in the harbour are the limiting factor for the traffic on the entire route. The wind directions effect on the manoeuvres is significant, and the optimal routes and manoeuvres on the harbour area should be planned in advance, based on the various wind directions.
The margin for manoeuvre that would be necessary for the retractable landing bridge to be entirely safe from a possible collision would make the structure quite heavy and expensive. In practice, collision damage in landing bridges cannot be fully eliminated, but the attachment of the landing bridge to the passenger bridge can be rendered in a way that enables the landing bridge to give in the event of a collision and the passenger bridge to remain intact. The manoeuvres and routes of the vessel can be adapted to ensure a small angle of approach to the pier, which means that the vessel would not be able to turn in such a way that its hull or deck structure would damage the structures on the pier – even under surprising conditions.
The risk of damage to the harbour structures can be further reduced by designing the structures to allow vessels to back up to the pier. This will usually naturally create a course where the vessel approaches the pier line at a small angle and with the bow outwards. This means that the bow would be the least probable part of the vessel to hit the harbour structures in the event of a collision; and even if it were to hit the structures, the keel line of the vessel would be sufficiently close to the pier line to form a sufficiently small reach of the bow for safety. Nevertheless, some vessels cannot approach the pier aft first due to the nature of their cargo, and the only alternative is to unload the cargo from the bow gate.