Signalman 1 & C - Historic Naval Ships Association

CHART SOUNDING MARKSScattered over the water area of each navigationalchart are many tiny figures, as in figure 9-7. Eachfigure represents the depth of water in that locality.Depths on charts are shown in feet, fathoms, or meters.A notation under the title of the chart provides the keyto its depth; for example, “Sounding in feet at meanlow water,” or “Sounding in fathoms at . . . .” Mostcharts also contain broken lines called fathom curves,marking the limits of areas of certain depths. A10-fathom (60-foot) curve and a 15-fathom (90-foot)curve can be seen in figure 9-7.CHART ISSUECharts used in the Navy may be prepared by theDefense Mapping Agency Hydrographic/Topographic Center (DMAHTC), the National OceanService (NOS), the British Admiralty, or otherhydrographic agencies. Whatever the source, allcharts used by the Navy are issued by the DefenceMapping Agency (DMA).The Defense Mapping Agency (DMA) Catalog ofMaps, Charts, and Related Products is a four-partcatalog published by the Defense Mapping AgencyOffice of Distribution Services (DMAODS). Itprovides a comprehensive reference of all DMA maps,charts, and related products that are available forinformation.NOTICES TO MARINERSThe chart and publication correction system isbased on the periodical Notices to Mariners, publishedweekly by the DMAHTC to inform mariners ofcorrections to nautical charts and publications. ThisFigure 9-7.—Navigational chart showing depths and fathom curves.9-6