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ACCIDENTS: No interaction between people, destructive interaction between ships

From the British Maritime Accident Investigation Branch’s Safety Digest 2/2011:

Narrative

A 2,800gt cargo vessel collided with a 58,000gt ro-ro vessel as it was overtaking the larger vessel in the confines of a buoyed channel when they were departing from a major port. Local pilots were embarked on both vessels at the time.

The ro-ro vessel had recently entered the channel from a lock, and was steadily increasing speed as the cargo vessel approached her from the starboard quarter. The cargo vessel’s pilot assumed the ro-ro vessel would quickly increase speed and pull ahead, and initially was not concerned as the distance between the two vessels continued to decrease.

However, the cargo vessel continued to overtake the other vessel, and with shallow water to starboard it reduced speed in an attempt to prevent a collision. Unfortunately this action was ineffective as the cargo vessel was now so close to the ro-ro vessel that hydrodynamic interaction occurred between the two vessels. The cargo vessel took a sheer to port and collided with the ro-ro vessel’s starboard quarter.

The cargo vessel’s engine was stopped, but she remained pinned against the ro-ro vessel for several minutes. The ro-ro vessel’s bridge team had been unaware of the close proximity of the other vessel until the collision occurred as both vessels had been monitoring different VHF channels.

The cargo vessel’s engine was then put astern and she slid aft, along the ro-ro vessel’s hull, until she came clear of the larger vessel. Both vessels suffered minor damage as a result of the collision, but were able to continue on their respective passages.

The Lessons

  1. The cargo vessel was overtaking the ro-ro vessel and was thus the give way vessel. However, the pilot of the cargo vessel assumed that the ro-ro vessel would quickly pull ahead, but by the time it was realised that this was not happening, it was too late to avoid a collision. The pilot of the cargo vessel made an assumption, based on scanty information, that the ro-ro vessel was increasing speed. He should have ensured that this was the case before coming so close to the other vessel that a collision was unavoidable.[REMARK: Something like a "before overtaking checklist" might be useful in helping pilots and bridge teams avoid critical errors in this potentially hazardous situation. It might as well contribute to avoid the dangers of the "control and command" style of navigation in restricted waters. Pilotage is a complex act that requires orchestration rather than one or two bright soloists.]
  2. Hydrodynamic interaction occurred between the two vessels when the cargo vessel drew level with the ro-ro’s starboard quarter. There was a strong attractive force between the two vessels due to the reduced pressure between the underwater portion of the hulls. Mariners should familiarise themselves with MGN 199 (M) Dangers of interactionin order to be alert to the situations when hydrodynamic interaction may occur.[REMARK: A video from the Ilawa Ship Handling Research Training Centre can give you a better idea of how this sort of interaction between ships is about. There is also some relevant footage from the Port Revel Training Centre on the same subject.]
  3. The bridge personnel were not functioning as a team on either vessel. They had been monitoring different VHF channels and those on the ro-ro vessel were not aware of the cargo vessel until after the collision. It is essential that every member of the bridge team remains vigilant and fully involved in monitoring the execution of the passage, and that a good all round lookout is maintained when the vessel is in pilotage waters as well as when she is at sea.[REMARK: It's about communication and awareness, after all. If overtakings are allowed in pilotage districts, everyone involved in the passage must be aware or made aware of this possibility and prepare for it accordingly.]

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