The opening separates ships designed or substantially adapted for hydrography from ordinary warships temporarily used for survey work. Frigates, sloops, and many smaller vessels could take soundings without becoming specialist survey ships. That distinction keeps the history focused on platforms whose equipment, spaces, or sustained employment reflected the survey mission. It also explains why the lineage is narrower than the much larger history of naval exploration and chart-making.
Chapter · 0:22-2:36
Specialist survey ships versus ships assigned to survey duty
Many frigates and sloops performed surveys, but that work did not make every vessel a specialist survey ship.