Kōrero: Charting the sea floor

These sounding devices were used by the Challenger, which surveyed New Zealand waters in 1874. Sounding equipment served two functions – the first and most important was to gauge the depth beneath a vessel. This was done by lowering a weight to the sea floor and measuring the length of the rope or sounding line. A secondary function was to determine whether the seabed below was rocky, sandy or muddy.