range of ship periods 



H_j' 



1.2 1.6 



a; (rad/sec) 



Period (sec) 



Figure 8. Response ratio for 6,000-foot wire at 5% rate, showing effect of mass/weight ratio. 



by a pneumatic spring cylinder. A pair of hydraulic 

 cyUnders are used to control the boom position when 

 operating in a "hard" (noncompensated) mode. With 

 the hydraulic cylinders in operation, the system is 

 capable of lifting loads in the same manner as with a 

 conventional crane. During operation in the com- 

 pensating mode the hydraulic cylinders are short- 

 circuited and, thus, effectively removed from system 

 operation. 



The pneumatic spring is the central component 

 of the compensating system, and its characteristics 

 determine how well the system operates. Figure 16 

 shows a simplified spring circuit. A pneumatic 

 cylinder is used to directly support the boom, pay- 

 load, and lift line. To obtain the required, relatively 



small, pressure changes over the boom stroke, 

 additional gas volume is provided from eight separate 

 high-pressure gas bottles that can be connected 

 together in a variety of ways using the manual cross- 

 connect valves (12C through H in Figure 16). 



Accumulator volume is also varied during 

 operation as a function of boom position to increase 

 the spring constant as the boom approaches the lower 

 limits of its travel range. To accomplish this, a 

 mechanical scotch yoke arrangement is activated by 

 pins attached to the boom. Three separate yokes are 

 used to control valves 12 A and B and 23, allowing the 

 accumulator volume to be reduced in three 

 incremental steps. Valve 23 is the last of the three to 

 be activated and completely separates the spring 



