The sensor actually develops an error signal which 

 is amplified, reversed in phase, and presented to the winch 

 motor through a phase amplifier and power control unit 

 (fig. 5). A synchro motor similar to the one mounted in 

 the sensor is mechanically geared to the winch drum in 

 such a way that the error signal is balanced out as the 

 winch motor automatically corrects for ship motion (fig. 4). 

 It is, however, important to place the sensor over the side 

 at a location close to where the oceanographic device or 

 other equipment is lowered to enable the sensor to feel the 

 same relative motion (fig. 5). Stretch in the lowering 

 cable and sway and surge of the vessel tend to offset the 

 degree of correction afforded by the generated signal, but 

 the use of the depth regulation equipment removes violent 

 tension overloads, thereby maintaining wire tension and 

 stretch at stable values. 



Operational Factors 



Factors to consider in the employment of the depth 

 regulation equipment are: 



(1) Under calm sea surface conditions, with the float- 

 ing platform on an even, steady keel, the depth sensor feels 

 no appreciable ship motion other than that caused by normal 

 flotation and develops only a negligible error signal, with 

 little correction needed. 



(2) When objects are lowered over the stern of a 

 platform, the roll effect is minimized, and the pitch and 

 resultant heave require the greatest correction. 



(3) When objects are lowered from a position amid- 

 ships on either side of a floating platform, the pitch is 

 minimized and roll requires the major correction. 



(4) Heave of a vessel caused by passing wave action 

 has to be corrected for, regardless of the location on the 

 floating platform from which the equipment is lowered. 



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