200660 Ballast operations

01 Mar 2006 MARS

 

On a large container vessel, the ballast tanks shared a common air vent-cum-overflow line, one running along each under deck passage. There were two overboard discharges on each line, one amidships and the other at the forward end, exiting the hull in way of the raised forecastle and above the waterline. Vent pipes were also led via penetrations in the upper deck to two independent vent heads. In port, it was standard procedure to shut the amidships overboard discharge valve on the shore side in order to avoid accidental discharge of ballast water overflow on to the quay, shore gantry cranes and other sensitive electrical installations.

The day after departure from a turnaround port, the chief officer began deep-sea ballast water exchange. The forward tanks were emptied and refilled without incident, except that the day's operations ended with an overflow. The next morning, the chief officer resumed the operations by deballasting one of the after double bottom tanks. However, on starting the pump, he observed abnormal readings on the console ammeter and pump suction and discharge manometers. The cadet also reported intense suction on opening the tank sounding pipe.

The pump was immediately stopped and investigations revealed the following:
  1. The overflow water from the previous evening's operation had formed a water seal in the forward section of the common vent-cum-overflow line.
  2. The amidships ballast overflow overboard discharge valve had not been opened after departure from port.
  3. As soon as the pump was started to deballast the after DB tank, the residual water in the vent overflow line was sucked into the air vent line of that tank, and operated the float check valve within. This prevented air from entering the tank from both routes, from vent heads on the upper deck as well as the overboard discharges on the common vent line. It caused a partial vacuum to develop inside the tank.

The problem disappeared as soon as the amidships overboard valve was opened and the residual water drained from the line.

 

200660

 

Root causes/contributory factors

  1. Failure to follow standard procedure of opening all overboard valves after departure from port;
  2. Inadvertent overflow during re-filling of forward ballast tank.

Other lessons

  1. Ballast operations must be preceded by a careful 'dry run' over the line diagram before starting a pump.
  2. All relevant valves that do not have a remote status indicator on the console must be physically checked and confirmed to be in the correct position.
  3. Handy checklists must be made for ballast line setting up and consulted before commencing every ballast operation.
  4. A warning notice must be permanently placed on the start button of the ballast pump reminding personnel to ensure critical valves are in the open position.
  5. Personnel must be given training in correctly interpreting remote gauges and indicators.

Editor's note: Due care and diligence must always precede the commencement of any ballast operation. The ballast management plan must be fully understood and followed by the operators. The ballast record book should ideally include completed and signed checklists, calculated stability conditions, stresses, draughts and trim at every stage of ballast operations.

There has been a spate of serious incidents in recent times, possibly attributable to hasty and incorrect ballasting/deballasting procedures. In one case, the side shell and internals in way of the ballast hold of a bulk carrier collapsed under partial vacuum conditions that occurred during deballasting with the hold vents shut. In another incident, a vehicle carrier nearly capsized during deep-sea ballast water exchange.

 

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