assemble the system by hand in about 5 hours and disassemble it 

 in about 3 hours. 



Launch and Recovery 



The assembled spar has been stowed, with the top end aft, 

 outboard of the starboard rail on the AGOR ship, USNS CHARLES H. 

 DAVIS, during transit. Owing to some flexibility, the spar can be 

 hogged tightly against the rail with the bottom end at the oceano- 

 graphic platforms, amidships to starboard. When the system is to 

 be launched the spar is supported by four hand cranked winches 

 clamped to the rail about 25 ft apart. These winches have 

 adequate line to reach into the water and are equipped with 

 special hooks in which the spar is cradled. By simultaneous 

 actuation of the winches the spar is lowered into the water 

 (see Fig. 4). As soon as the spar is floating the hooks are 

 cleared and retrieved. Next, the virtual mass containers and the 

 reserve buoyancy ballast are lowered into the water. These are 

 connected to the spar by a length of chain. The ballast causes 

 the containers to fill rapidly and the load is eased down onto the 

 spar by a 3/16 in. wire rope which is connected to the bottom of 

 the containers. At this time the spar is partially righted and 

 is most vulnerable because wave action flexes it severely. 



Launching the instrument array onto the spar cable by a poly- 

 propylene tag -line tilts the spar to vertical and leaves about 

 16 ft of spar above the water line. The other end of the polypro- 

 pylene tag -line is terminated with a lighted float and is cast 

 free of the ship. This configuration allows the array to be 

 recovered or changed without having to recover the spar. Spar 

 recovery is the reverse of the launch procedure and requires about 

 half an hour with six men. 



Spar Motion 



Accurate information on actual sea conditions during the 

 October 1968 cruise aboard the USNS CHARLES H. DAVIS, off the 

 Washington coast, was hard to obtain. No wave instrumentation was 

 available; therefore wave heights were estimated by observation of 

 excursion against the side of the ship and on the spar pole. Wave 

 periods were noted by timing crests passing the spar. These 

 values, in combination with wind speed, gave approximate Sea States 

 4 - 7 on a scale of 9. 



Records of vertical spar motion were obtained by reading the 

 pressure fluctuations of a Vibrotron (pressure sensor) located on 

 the array. Pressure variations with periods of less than a few 

 minutes were assumed to be caused by spar motion. In this range 

 most of the motion occurred with periods between 5 and 20 sec. 

 This matches the expected spectrum of surface wave and swell periods, 



176 



