Reliability of navigational charts and confidence in the bathymetric data presented

Navigational charts are a basic source of information for seafarers. But how accurate and reliable are they? How much trust and confidence can be put in them? Unfortunately, the answer is not so simple; it is far more complicated than merely saying that one chart is accurate and reliable while another is not. However, any seafarer navigating in unfamiliar waters should have the necessary skills. It is a great challenge – some may say an impossibility – to keep the thousands of navigational charts up to date. But exactly how out of date, how inaccurate, are the chart data? Chart users will have a better idea now that the Hydrographic Office is gradually implementing a new chart feature called the Zone of Confidence (ZOC) box which replaces the Source Diagram that is currently in use on large-scale charts. Source Diagrams, and now the improved ZOCs, assist seafarers in assessing hydrographic survey data and the associated levels of risk of navigating in a particular area. According to the new edition of the International Hydrographic Organization (IHO) specifications, S-4 navigational charts will provide more information on ZOCs. The current paper discusses these new regulations.