THE PROBLEM OF DEPTH CONTROL 



The collection of oceanographic data often requires 

 that underwater equipment be maintained at a constant 

 height above the sea floor or towed at a constant depth be- 

 low the sea surface level. Measurements of temperature 

 and light intensity, collection of water samples, acoustic 

 ranging and listening with lowered transducers, recordings 

 of wave movement, and underwater photography are some 

 of the operations that require depth regulation. 



Varying sea surface conditions, however, impose 

 great difficulty in maintaining depth control. The wind- 

 stirred surface of the ocean causes ships to roll, pitch, 

 yaw, surge, sway, and heave. Figure 1 (adapted from a 

 sketch by R. Marra 1 ) shows how wave action moves a 

 vessel. 



SURGE 



HEAVE 



Figure 1 . Ship motion, 



1. Pearlman, M. D. , "Waves, Ships and Seaworthiness," 

 Sea Frontiers, v. 9, p. 310-316, Christmas 1963 



