Cardinal marks indicates where the best and safest water may be found and is used in conjunction with a compass. The mark shows where the mariner has safe passage. A cardinal mark may indicate: the deepest water in an area, or the safe side on which to pass a danger, or a feature in a channel such as a bend, junction or an end of a shoal.
Isolated danger marks designate an isolated danger of limited extent which has navigable water all round it, for example an isolated shoal, rock or wreck.
Safe water marks indicate that there is navigable water all around the mark for example mid channel or landfall buoy.
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