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How to Use Admiralty Charts


Admiralty charts
are nautical charts produced by the United Kingdom Hydrographic Office that detail all nautical passageways around the world. With over 3000 of these charts in existence, these informative displays are protected by Crown Copyright and have been used by yachtsman for hundreds of years. Learn more about admiralty charts in the guide below.

Reading an Admiralty Chart


1.    Large scale admiralty charts cover approaches and entrances to harbour, providing essential information to yachtsman embarking upon a long haul trip around the world. However, the UKHO also produce medium and small scale charts which cover heavily used coastal areas and open waters respectively.

2.    These nautical charts include substantial amounts of data, all of which the responsible yachtsman should learn during a boating lifetime. Charts display data and landmarks such as depths, coastline, buoyage, underwater and above water contour lines, tidal information, hazards and seabed composition information, prominent landmarks, traffic separation schemes and lights and lighthouses. However, these maps are continuing to evolve over time to provide as practical data as possible to the modern day yachtsman.

3.    Admiralty charts use Mercator projection, which is a cylindrical map presentation created by Geradus Mercator all the way back in 1569 – and it still remains the standard nautical chart projection to this day. This system allows bearings to be transferred to charts directly, with allowances made for magnetic variation and deviation to ensure further accuracy. Straight lines drawn on a chart under the Mercator projection represent lines of constant bearing, even if in real life the lines are not straight.

4.    Finally, anybody using an admiralty chart should try and gain access to the very latest nautical information, as the condition of the seabed and landmarks on the shore can change and appear over time. In fact, it can be essential to have updated charts in terms of your insurance – should you have an accident, the insurance company will question the age and accuracy of your charts before agreeing to pay out.