200416 Changing Charts

Changing Charts
MARS Report 200416

I have just finished reading the article "Good watchkeeping practice" by Captain Syms in the January 2004 Seaways, and his "Worry Rule". His Rule 1, - "continuously compare all sources of position information", brought to mind an incident in 1974 of a very serious navigational error.

I was Master in a well known company, running good ships, where officers could expect to be retained for a lifetime. We were outward bound down the Channel, between the Cherbourg Peninsula and Ushant, well offshore, and during the hours of darkness. We were unable to see navigation marks and lights so we were relying on Decca Navigator. I was called at about 0700 by the Chief Officer, who was concerned that he had not raised the land. On the bridge, making use of the radar at extreme ranges and some degree of guesswork, we found ourselves to be at least 20 miles away from the plotted Decca position. With the position re-established and the ship in safety, I was able to go for breakfast, but after that I had an investigation to carry out.

The charts showed regular and evenly spaced positions during the night by Decca Navigator. It was rather puzzling, until I checked the change from one chart to another at 0230. The Decca co-ordinates had been used to transfer the position, without any attempt to also check Latitude and Longitude, or check by bearing and distance from a fixed point. The wrong Lane letter had been used, and with only two lines of position, there was no cocked hat. Because the ship was not apparently keeping to the course line, the 2nd Officer rubbed out the line and drew a new course line - instead of consulting the Tidal Atlas and applying set, hour by hour as the tidal stream changed. This was complacency and carelessness of the highest order. When spoken to privately later in the morning, I expected some kind of remorse and an apology. How wrong I was! There was only a surly response from aEven though the Decca Navigator is now somewhat obsolete, the lesson learnt here is to take great care when transferring position from one chart to the next.

Even though the Decca Navigator is now somewhat obsolete, the lesson learnt here is to take great care when transferring position from one chart to the next.