I . Introduction 



In August 1980 an acoustic array, referred to as MAVA (Moored Acoustic 

 Vertical Array), was deployed by the Naval Oceanographic Office off the coast 

 of France and moored in a depth of 4550 meters. Attempts to recover the array, 

 which was equipped with dual acoustic anchor releases, were unsuccessful. One 

 release failed to respond in any way to surface interrogation while the other, 

 although functioning in the transpond mode, would not release on corrmand. 



During December of 1980 MAVA was successfully recovered using a tech- 

 nique which this report will describe in detail. 



II. Design Goals and Considerations 



The basic goal of the recovery operation was to retrieve the MAVA 

 instrument package and the data it was expected to contain. 



MAVA is a single, taut line array which consists of a positively 

 buoyant subsurface instrument package and a vertical hydrophone array. The 

 array is attached to an anchor by means of k inch diameter kevlar line, a 

 dual anchor release package and h inch diameter 3X19 construction wire 

 rope, figure 1. In this particular case, MAVA had been configured to position 

 the instrument package at a depth of 1900 meters. The water depth was 4550 

 meters at the mooring location. The anchor releases were located 100 meters 

 off the bottom. 



Bathymetric and geophysical data for the area indicated that the muddy 

 bottom was nearly flat with no indications of obstructions. 



Ocean current data for the area, although sparse, indicated surface 

 currents up to .5 knot diminishing to .1 knot at the bottom. 



Statistical weather information for the area indicated that the condi- 

 tions would be poor to severe with the probability of the latter increasing 

 significantly in January and February. The decision was therefore made to 

 attempt the recovery early in December. 



An important consideration in planning the recovery operation was 

 navigation. Loran C was not available in the recovery area for geographical 

 fixes. The only available means of navigation was Satellite Navigation and 

 dead reckoning was required between satellite fixes. Accurate satellite 

 fixes were generally available e\/ery one to two hours. 



During the initial stages of selecting the recovery technique, 

 several candidate schemes were considered. Submersibles or remote vehicles 

 were found to be unavailable. Towing a cable with a large grapnel at the end 

 and trying to snag the array seemed to have little chance for success. A 

 technique used successfully by Woods Hole Oceanographic Institute at lesser 

 depths was also considered. Briefly this consisted of circling the array while 

 paying out cable on the bottom. Srapnels were attached periodically along the 

 cable length. Having circled the array, the ship would steam off pulling the 

 cable and grapnels around the array in an attempt to cut or snag it. 



