Many nations publish Sailing Directions for their home waters, where they are the International Hydrographic Organization's (IHO) primary charting authority. However, the most widely used Sailing Directions product is the United Kingdom Hydrographic Office's, 'Admiralty Sailing directions' (ASDs)( a.k.a. Pilot books). The ASDs, sold under the Admiralty brand, provide the most comprehensive geographic coverage of coastal routes worldwide. They are designed to supplement and enhance the data shown on British Admiralty Nautical Charts, by describing routes for seagoing vessels, relative to coastal features. Ocean routes are covered by the Admiralty book 'Ocean Passages for The World' (Abbrev. OPTW. Nautical Publication NP136), which describes Offshore routes separately for power driven vessels, and low powered / sailing vessels.