As UK MAIB reports in its most recent Safety Digest, one bright spring morning, just before high water, a workboat berthed in a lock on its way to support diving operations in the adjacent dock.
The incident
A small pulse of water entered the lock when the lock gates were opened; as a result, the workboat shifted on its slack moorings and the shore gangway started to twist. The master lost control while using the engines to reposition alongside and the workboat ended up at 90° to the lock walls. The gangway fell to the lock bottom. The workboat was eventually secured alongside and the gangway was recovered.
When the workboat went to lock out of the dock at the end of the day, the master was advised that the lock operator planned to substantially drop the water level in the lock. Language difficulties hindered the communication but, after several attempts, the lock operator received a positive acknowledgement from the
master that they understood these intentions. However, the workboat’s mooring lines were not adjusted as the water levels in the lock started to reduce and the workboat momentarily listed to starboard as some of the mooring lines became rigid. A deckhand used a knife to cut one of the breast lines to release the tension, causing the line to whip out and the vessel to jolt back onto an even keel. Luckily no one was hurt, either on the lock or on board. The workboat returned to its home port without further incident.
Lessons learned
- Plan → The rise and fall of water in a lock can be significant and pulses of water can occur when the lock gates are opened. This is a foreseeable event and those involved should plan ahead to assign individuals to manage the mooring lines and equipment to the shore. Untended lines can part with the risk of snapping back, which could easily result in serious injuries or damage to the vessel.
- Communicate → The lock operator tried several times to communicate with the workboat master about water level changes in the lock. However, the master did not understand the message despite their positive acknowledgement. Effective two-way communication prevents accidents.
- Observe → Vessel crews need to be alert to emerging problems. The mooring lines did not suddenly become rigid and the issues at the gangway happened over time. Crew vigilance is vital to maintain safety and prompt actions reduce the risk of significant problems. At times, personnel ashore were watching what was happening and closed-circuit television (CCTV) captured the events. Active bystanders and security staff monitoring CCTV can also make positive contributions to safety and warn of developing situations.
- Risk → The risk to people takes priority over damage to equipment. The crew struggled valiantly to save the gangway before it fell to the bottom of the lock, risking their own personal safety when it may have been better just to let the gangway go and stay safe.
