CHIRP analyzes an incident where a vessel touched bottom during canal transit, and provides lessons learned to keep similar accidents to take place in the future.
The incident
A tanker was transiting a canal with 2 pilots on the bridge in addition to the master, chief officer, helm and lookout. The pilot ordered a turn to starboard later than planned, but this was not challenged by the bridge team.
As the vessel approached the channel’s port side the bank effect pulled the stern to port just as starboard rudder was applied. In combination, these caused the vessel to cross to the channel’s starboard side where bank effect pushed the bow to port. The vessel re-crossed the channel and touched bottom on her port side, breaching the water ballast tanks.
The vessel was directed to a safe anchorage for damage assessment by the company, flag state, class, insurers, and the port authorities. An investigation revealed that this type of manoeuvring incident frequently occurred in this canal.
Probable cause
According to CHIRP, the causes of this incident were in place long before the vessel touched bottom. During the planning stage, the available depth of water and the narrow breadth of the channel should have prompted the master and navigator to consider the possibility that bank effect and squat could affect manoeuvrability and to determine the speed at which these might take effect.
If this speed was below the minimum steerage speed, then the use of tugs should have been considered. The need for tugs should have been revisited during the master/pilot exchange.
The port authorities knew that vessels often touched the bottom in the canal, which could indicate out of date or inaccurate chart data, the need for maintenance dredging, or missing or inaccurate aids to navigation. Suitable control measures could have included the requirement for deep-draughted vessels to take tugs to control manoeuvring in the channel, or at least the provision of navigational warnings of the risk of bank effect and squat.
Integrating a pilot into the bridge team requires a comprehensive and continual exchange of information, such as counting down to the next planned course
alteration and challenging the pilot if this is delayed
said CHIRP, adding that it also includes monitoring the rate of turn and the vessel’s position in relation to the planned navigational track. It is good bridge management to discuss future intentions such as course alterations ahead of time to allow everyone to understand what is about to happen, and when, allowing time for challenges to be aired. In this case, the master had insufficient time to intervene and rectify the pilot’s late actions.
It appears that neither the pilot nor the bridge team recognized that the vessel was experiencing the bank effect after the bow’s initial swing to starboard, or if they did, they did not take corrective action.
Human factors
- Local Practices: Does the ship’s master/pilot exchange format include reference to bank effect, squat, and their calculated onset speeds in relation to your vessel’s minimum steerage speed? Does it call for tugs to be employed in this situation? Does the pilot embark early enough to properly discuss navigational intentions and exchange all pertinent information, allowing time for clarifications and challenges before handing over the conn?
- Culture: How is the pilot integrated into the bridge team? How can this be improved in the vessel?
- Communication: Does the bridge team proactively brief future intentions? Is there a discussion about known hazards or a history of previous incidents in the port that you need to be aware of and, if so, does this prompt a review of your navigational risk assessment prior and the implementation of additional control measures such as ordering tugs?
- Situational Awareness: Does the bridge team continue to monitor the navigation and position of the ship after the pilot has boarded?
- Capability: Is there the ability to identify hydrodynamic interactions such as bank effect, including any unexpected increase in swing or turn rate?
