"The 1857 British Admiralty survey was carried out by Hutchison under the direction of a Captain Henry Mangles Denham F.R.S. who had been tasked with surveying parts of the south-west Pacific in HMS Herald. The chart of this survey, engraved in 1859, had the high soundings density one would expect with a modern hydrographic survey and it clearly marks a significant departure from earlier mapping efforts of Sydney Harbour. The area covered was from 1.5 miles (2.4 km) seawards of the harbour entrance west to Five Dock Bay. However sounding densities were relatively sparse west of Cockatoo Island, where a new dry dock, Fitzroy Dry Dock, was opened in late 1857. The survey and initial chart production took approximately two months."
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