Joseph Dayman was a British hydrographer. He became a lieutenant in the Royal Navy in 1843 and in 1851 studied steam at Woolwich dockyard. While still a lieutenant he observed some occultations along the South African coast, at Durban and Port Elizabeth, for the determination of longitudes. The results were reported in the Monthly Notices of the Royal Astronomical Society in 1856.
Following the wreck of the Birkenhead on an uncharted reef in February 1852, the British Admiralty ordered that a survey of the Cape coast be undertaken from Cape Point to Cape Augulhas. The task was entrusted to Captain Dayman and Lieutenant H.G. Simpson. They linked their survey to several beacons near the coast that had formed part of the southern extremity of Thomas Maclear's* geodetic survey some twenty years earlier. Their work resulted in a much more accurate chart of that portion of the coast than had been available before.
During 1857-1858 Dayman, then Lieutenant-Commander first in the Cyclops and then in the Gorgon, made deep sea soundings in the north Atlantic Ocean between Ireland and Newfoundland for the laying of the first transatlantic telegraph cable. His report was published by order of the Admiralty in London in 1858. The next year Commander Dayman, in the Firebrand, extending his soundings to the area between the Azores and England for the laying of a cable to Gibraltar. The results were published by the Hydrographic Department in 1859.