200538 Unaccounted Ballast

Narrative

Two days before arrival at a river entrance, a Company Vessel was advised by the agent of a draft restriction of 36.1 ft (11.00 m) due to the low water flow in the river. This required the vessel to internally transfer some cargo in order to reduce the draft from 37.5ft (11.43m). The vessel transferred 332mt of cargo from cargo tank 1 port into 7 port and starboard and pumped out water ballast tanks 6 and 7 port and starboard. This procedure was agreed with the Charterers in order to arrive with draught of 36.1 ft.

On arrival, the vessel successfully underwent a Coast Guard Certificate of Compliance and Security Inspection. After some time at anchor awaiting berth readiness, the vessel resumed her passage to the terminal with a river pilot on board. At 0336, the vessel ran aground in way of ballast tank No.1 starboard. The weather at the time of the accident was fine with good visibility and the current ebbing at 3 knots.

Sounding of all the ship's tanks revealed water in ballast tank 1 starboard, level 7.9 m and not rising. Visual checks around the vessel revealed no oil or cargo leakage, which was confirmed by unchanged cargo tank liquid levels. Attempts to sound the depths around the vessel were frustrated due to the strong current. At the same time, depth soundings were taken by one of the assisting tugs. The vessel's situation was assessed as stable and therefore the Authorities requested the vessel to wait until the stability calculations were confirmed by experts.

The expert's stability calculations and proposed transfer of cargo and ballast was sent to the managers but did not match the vessel's actual draught and trim. Further investigation on board revealed that the vessel had 600mt of unaccounted ballast. This was due to the fact that the design of the sounding pipe for water ballast tanks 1 port and starboard would not allow the sounding tape to go down all the way. The ship's draught was well known and within the maximum of 11 meters, however, the weight distribution was different from what was believed on board. After the facts were established and calculations corrected, the proposal from the experts was sent to the vessel for local Authority approval. 14.5 hours after the vessel grounded, she was re-floated with the assistance of one tug.

The master went down to his office about 30 minutes before the grounding, to prepare the pre-arrival documentation. This fact has been considered and a thorough investigation along with root cause analysis, using the computerised model Reason 6 has been carried out. This led to the conclusion that the master not being on the bridge had no direct bearing on the grounding, as the Master would be guided by the Pilot's recommendation, and would probably be quite happy with the vessel's position as she was still within the buoyed channel.

With the benefit of hindsight and the result of the Risk Assessment carried out after the accident, it would have been prudent for the Master to stay on the bridge, bearing in mind the special circumstances that night - unusually low and still dropping water, and vessel drawing maximum allowed draught.

Main Causes

1. The Pilot was of the opinion that the starboard side of the buoyed channel was deep enough for the vessel's draught. This view was supported by the navigational marks (buoys). This was obviously a wrong assumption, however we cannot establish whether this was due to the Pilot's negligence or lack of information available to him.
2. The recommended safe draught was too deep. The vessel had transferred cargo and ballast in order to meet the recommended draught, however this proved insufficient. Why this draught was regarded as sufficient, we don't know and have to wait for the Port Authorities report along with the Pilots Authority's Investigation report.

Lessons learnt

1. It is the responsibility of senior officers to consider the situation, particularly in matters of safety. They should act upon the information available to them to make sensible decisions, however, in this particular case we strongly believe that the Pilot service, especially for the river ports, should be accountable for navigational errors. The Master of the vessel, although responsible for his vessel, heavily depends on the local Pilot's expertise. He has no chance to verify or question the Pilot's ability to safely navigate the vessel, especially when all other factors (buoyed channel, information received from the agent and port authorities) seem to back up this expertise.
2. Good log book keeping is essential, as the ship's staff will never know when it will be called for. In this particular case it helped us greatly to establish all the facts as the record keeping was very good.
3. Efficient Ballast Management is crucial. It calls for full co-operation between the departments - engineer officers responsible for bunkers and deck officers responsible for fresh water, ballast water and cargo weight distribution. This accident showed a weakness in the onboard system. Tanks with electronic gauges were never manually sounded, however records indicated no water in water ballast tanks. This fact was only spotted by the third party stability calculations, when theoretical draught was compared with ship's actual draught. Ship's staff were quick to explain the discrepancy as "unknown" and applied a "draft correction" in an attempt to explain the difference.

 

FEEDBACK March 2006

MARS report 200538 in September's 2005 Seaways caught my eye. The subjects discussed were unaccounted ballast and draft. A vessel grounded while entering a draft restricted river entrance, I would like to add a few general observations to the 'lessons learnt' section of the report.
When charterers, brokers or agents send maximum draft instructions to the vessel, it is imperative to show if the draft pertains to seawater, brackish or fresh water. For example if a panamax vessel arrives at the bar with 40 feet draft in seawater, she may immerse to more than 41 feet while steaming up a fresh-water river. If that river was dredged to 40 feet fresh water, the ship runs the risk of running aground.
Second, many ships have cargo computers that calculate the draft based on all the weights on board the ship. The hydrostatic tables of a new ship will show what has been included in the weight of the light ship. Furthermore, it shows the capacities of cargo compartments, fuel and ballast tanks.
Provided everything has been entered correctly (either by keyboard, or on a tanker via the electronic gauging system), the computer will more than likely show calculated draft on perpendiculars; not observed draft. Since it is impractical to hang over the side of a moving vessel to obtain the draft, and since mechanical draft gauges are notoriously inaccurate, it is tempting for a chief officer to use calculated draft rather than actual draft. If calculated draft is used, it is very important to enter into the computer the proper salinity of the water the ship is floating in. A related problem is that salinity may change quickly while navigating in a tidal river. Of course, squat influences draft as well.
The report mentions that 600mt was unaccounted for. This may lead to the assumption that the people operating this vessel (on board as well as ashore) were not very familiar with their ship. Over the years, tank gauges may fail, and sludge may build up in ballast tanks, One of the best ways to check the accuracy of tank gauges is to open the manhole and do a visual check for emptiness, or hand-gauge the tank. Instead of 600mt ballast, in a draft-restricted case, the ship could have carried 600mt extra cargo. If this was a chemical carrier and freight was $100/mt, the owner lost $60,000 in revenue for this, and for possible future voyages.
To calculate a vessel’s proper cargo capacity, it is good practice to perform an occasional deadweight survey.