Blue Water

I’m a great fan of electronic charts, GPS and integrated bridge systems, but like many old-time navigators I worry about the erosion of traditional seafaring skills when it comes to safe navigation and piloting. When teaching navigation courses in the Navy, I spent years pounding into the heads of my students the Prime Directive – never place 100% reliance in any single aid to navigation. Always verify everything from a second source.

A case in point.

Shortly before midnight, on June 10, 1995, the cruise ship Royal Majesty, with more than 1,500 passengers, grounded on Rose and Crown Shoal about ten miles east of Nantucket Island. The weather was clear, and the ship was equipped with a state-of-the-art integrated navigation system. The bridge watch team was experienced and fully staffed. Still, the ship managed to run hard aground on a well-charted shoal. The ship’s actual position turned out to be 17 miles from where the watch officers, relying on their electronics, believed it to be.

The accident investigation traced the error to a GPS antenna cable that jarred loose. This caused the electronic charting system to default automatically to a dead reckoning mode, updating its position by heading and speed inputs in the absence of GPS position inputs. The error went undiscovered for 34 hours.

So why did none of the watch officers notice that the ship was off track? Why did they not compare the charted position against the radar picture of the shoreline, or take compass bearings from visible charted navigation aids, or even verify the identification and characteristics of nearby buoys against the chart. No one even seemed to notice that the GPS position readout did not match the coordinates displayed on the Loran-C receiver, which was mounted right next to the GPS.

The National Transportation Safety Board (NTSB) concluded that the primary cause of the accident was the crew’s overreliance on the automated features of the integrated bridge system, ignoring several important “cues” that should have alerted them to the ever-accumulating navigation error in their electronic charting system over the 34-hour period.

Mind you, electronic charts and integrated bridge system technology has come a long ways since 1995, and these systems are now designed to ensure that a broken GPS antenna cable would set off plenty of audible and visual alarms for the master and bridge team. It wasn’t the GPS that caused the accident (although it was heralded by many at the time as the “first GPS-assisted grounding”). It was the navigation team’s fixation on the electronic systems and unwillingness to follow the Prime Directive of Navigation.

You can download the NTSB accident report from http://www.ntsb.gov/publictn/1997/mar9701.pdf. It’s written in a simple and direct prose style that is easy to read, and I highly recommend it to anyone seriously interested in ship navigation.