Mariners must be aware that on many charts still in use, a correction has to be applied to a satellite derived position referenced to WGS84 before the position is plotted on the chart, warns the latest issue of the London P&I Club’s Stoploss Bulletin.
Navigating officers should always check the charts for information about corrections that need to be applied to satellite derived positions when preparing a passage plan and alert the navigators to any existing corrections which are required before positions are plotted on the individual charts.
this issue is also emphasised by an incident in which a ship grounded as a result of total reliance on GPS, coupled with a failure to recognise that a significant correction had to be applied to GPS positions before they were plotted on the chart. During a coastal passage, a containership ran aground after a navigating officer commenced a significant alteration of course about half a mile before he reached the intended alter course position.
Investigations suggested that the officer was using no means other than GPS to navigate and, even though the ship was on a regular schedule, was wholly unaware that a significant correction had to be applied before GPS positions could be plotted onto many of the charts used in the service.
A more detailed passage plan would have alerted the inexperienced officer to the danger and required him to cross-check his position by more than one method.
The latest edition of The London P&I Club’s loss prevention publication StopLoss is available here.