Order 1a, 1b, 2 Survey

The S-44 survey orders grade hydrographic surveys by required accuracy and seafloor coverage. Order 1a demands full bottom search and feature detection in waters where the seafloor may not clear the keel; Order 1b allows partial coverage where underkeel clearance is ample; Order 2 covers deeper water where a general depth description suffices. Edition 6 adds the tighter Special and Exclusive Orders above these for harbors and channels.