The West of England Club informed that it has experienced two claims where, in separate incidents, a container vessel and a tanker inexplicably lost control whilst departing port under pilotage.
Namely, one vessel made contact with an oil jetty causing notable damage to the face of the berth, while the other left the navigable channel, hit a light beacon, then ran aground on top of a submarine pipeline. Both incidents caused significant claims.
In each case the vessels were following the customary route outbound from the port concerned, when at relatively slow speed and because of reasons unknown to the bridge team, they started to turn such that they were almost perpendicular to their original course by the time they made contact.
Neither vessel could stop the turn by, in one case, applying full opposite rudder along with the use of the bow thruster, and in the other, despite using full ahead on the main engine with full rudder.
Each incident took place when the vessel was passing through an area where strong tidal streams / cross currents could be experienced, where the tidal stream passed between two adjacent islands, and where there was a channel which was perpendicular to and joined the main navigable channel along which the vessel was proceeding, from which a strong outflow existed.
In these cases, despite the fact that both vessels were proceeding at sufficient speed to maintain steerage way, the rudder turning force available at low speed was overcome by the force of the tidal stream / cross current acting on the substantial area of the submerged hull abaft the pivot point. The large turning moment created by this force led the stern to be pushed sideways, with the rudder force and in one case with the engine being robustly kicked ahead, being insufficient to counterbalance this turning moment.
According to the West of England Club, these two cases show that although a low speed can give more time for watchkeepers to assess the navigational situation, there may be circumstances where strong localised tidal streams / cross currents are existing and subsequently where a higher speed may well be prudent to increase the effectiveness of the rudder and reduce the time the hull is exposed to the external water force.
However, a vessel should always comply with any applicable speed limits imposed within harbour limits. Until now, locations where strong localised tidal streams / cross currents may exist should be identified during passage planning and marked on the plan accordingly. Moreover, the pilot should be used as a source of local knowledge in this regard.
Once directional control of a vessel is lost and attempts to stop the ship are unsuccessful, the vessel should be slowed as quickly as possible by use of astern movements on the engine and consideration given to dropping the anchors, providing it is safe to do so with no seabed obstructions.
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