Definition
In current British and NATO practice a shackle is 15 fathoms, that is 90 feet or 27.4 metres, and the same length is called a shot in United States usage. Chain lengths are joined by detachable links and marked with turns of wire or paint so the officer on the forecastle can report cable veered, for example three shackles in the water. Older Royal Navy practice used a shackle of 12.5 fathoms.
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