Lessons learned: Grounding in unsurveyed waters

by The Editorial Team 

May 11, 2021

In its latest casebook of marine casualties, Swedish Club describes an incident where a RoRo vessel run aground in unsurveyed waters.

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The incident

A 50,000 GT RoRo vessel had been loading in a European port. The navigation officer had prepared the passage plan for the voyage to the next port of call which was in central America. Prior to departure the Master received weather routeing for the passage, which suggested a route over the Silver Bank and via the Windward Passage.

The navigation officer planned the route in the ECDIS and on paper charts and discovered that the minimum depth the vessel would encounter was at the Silver Bank where the water depth was 16 metres according to British Admiralty chart 3908.

The vessel’s draft was 7.5 metres, so a 16-metre water depth was considered acceptable as per the company’s ISM under keel clearance procedure. The procedure stated that there had to be a minimum of 20% under keel clearance of the maximum draught.

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‘Inadequately surveyed’ warning

On the British Admiralty chart the Silver Bank is marked ‘Inadequately surveyed’ in three places. On the route planned by the navigation officer there was no specific mention of inadequately surveyed waters. The navigation officer did not consult the Admiralty Sailing Directions when preparing the passage plan.

After checking the entire route on the ECDIS and on the paper charts, the Master decided to follow the route suggested by the weather routeing company.

The passage was uneventful over theAtlantic from Europe and the vessel maintained a speed of 13.5 knots. Shortly after entering the Silver Bank the vessel’s bow suddenly swung to starboard, which caused a list for about 3 to 5 seconds, with excessive vibration.

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The OOW changed to hand steering. A couple of minutes later the vessel’s bow swung to starboard, but this
time with less vibration.

The vessel’s bow swung a third time to starboard and listed for about 3 seconds, with vibrations. After carrying out a damage assessment it was found that the forepeak tank and a water ballast tank had water ingress. All the fuel tanks were intact.

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Vessel repaired in dry dock

The vessel arrived at the destination port, discharged the cargo and carried out an in-water survey. It was found that the tanks had beenpunctured as the vessel had touched bottom. The vessel had to be repaired in dry-dock.

Lessons learned

• The vessel had on board the Admiralty Sailing Directions NP 70, West Indies Pilot, where it is stated that Silver Bank has been inadequately surveyed and it is not advisable to attempt to cross it. The sailing directions had not been reviewed before or after making preparing the passage plan. It is important to ensure that all reference literature is used when making a passage plan.

• It is important to perform a two-person check for critical operations such as a passage plan. It is more likely that another person will find a mistake rather than just carrying out your own double checking.

• The ECDIS chart information is based on data from the paper charts. If the quality of the data in the paper charts is poor, then so will the data in the ECDIS charts cell be. Each chart cell contains a CATZOC code (Category Zone of Confidence), which indicates the accuracy of the data in the cell.

• As part of the passage plan appraisal the navigation officer should check the quality of the data. The sailing directions will give good information about routeing and will also mention recommended routes. There are many areas in the world where the chart data is uncertain so even if the chart is vectorised as per IHO standards, it is necessary to check the quality 9.1 of the data used.