With a US Navy investigation underway to assess the circumstances surrounding the USS Guardian grounding that occurred in Philippine waters at 02.25 on 17 January local time there are lessons already to be learned: Charts are not infallible even if they are on screen and it is not wise to navigate to fine tolerances with the aid of GPS when the underlying data is less accurate than the GPS.
An inaccurate chart is not a defence – not bumping into bits of ground remains the master’s responsibility.
Much of the Philippine waters have not be surveyed for 50 years or more, an issue highlighted when the Greenpeace ship Rainbow Warrior also grounded on Tubbataha Reef in 2005. The chart in use showed the reef 1.5 miles from where it actually was.
The digital chart aboard USS Guardian, an Avenger-class mine countermeasures vessel, showed a position about eight nautical miles in error. At the time of the grounding the vessel was attempting passage through a channel just half that width.
Many Philippine charts have not been re-surveyed in some 80 years. Transferring this aged data to an electronic chart does not increase its accuracy. The current NGA chart for Tubbataha reef appears to be the 1986 edition, based on Philippine charts of 1975 and earlier.
According to a source in the Philippine Coastguard “With the 1940 or 42 charts by NAMRIA, there might really be a problem with that’s why we are advised to at least have a difference of Three nautical miles from the shoreline, we have to assume that there is one nautical miles changes in the chart already”.
NAMRIA tells Maritime Accident Casebook that the last hydrographic and topographic survey covering Tubbataha Reef was conducted in 2006 using single beam echosounder for the hydrographic data, 2008 is the latest hydrographic survey using multibeam echosounders. The chart was first published last May 2009 and the reef is marked as a restricted area on current charts.
On Friday, 18 January, the US National Geospatial-Intelligence Agency, NGA provided the US Navy with preliminary findings of a review on Digital Nautical Charts (DNC) that contain inaccurate navigation data and may have been a factor in the Guardian grounding.
This followed the realisation by NGA that there might be a potential inaccuracy regarding the Tubbataha Reef digital chart. NGA has reviewed data from more than 150,000 square nautical miles in the surrounding area and found no additional errors.
The incident may also lead to a review of the $30m 2006 joint hydrographic survey agreement between the US Navy and the Philippines after nine years of negotiations. The project was to use advanced sonar technology to map shipping lanes, harbors, and ports throughout the Philippines. However an incident involving a Philippine Maritime Police Patrol vessel firing warning shots against a US Navy survey vessel in January 2008 led to US Navy surveys being restricted to within four nautical miles of the coast.
The project was expected to generate some $300m in commercial value.