A 15-ton trussed aluminum linear array, whose length is about 600 

 feet and whose cross dimensions are a few feet, and a 1-5/8 -inch diameter 

 6 X 37 Special Flexible Hoisting wire rope (USS) are selected as a numerical ex- 

 ample. A curve is computed giving, for each frequency, the maximum safe in- 

 put amplitude for any length of the cable up to 20, 000 feet. This curve shows 

 that, as the frequency increases, the maximum safe input amplitude decreases 

 sharply. At a frequency of 1 rad/sec (six- second period), the maximum safe 

 amplitude is 20 feet, while at a frequency of 2 rad/sec (three-second period), 

 it is only 1.7 feet. This shows that the vessel must be rather stable if this oper- 

 ation is to be carried out successfully in a moderately rough sea. Also, it indi- 

 cates that ways in which the cable can be attached to the vessel are limited. 



Two obvious ways of attaching the cable to the vessel are: (1) from 

 the center of gravity, and (2) from the side through a boom. In the first, heav- 

 ing motions of the vessel in beam seas will be critical, while in the second, rol- 

 ling motions in beam seas will be the most critical. Amplitude response curves 

 for heaving and rolling of Cuss I (see footnote of page 27 for a description of this 

 vessel) in beam regular (sinusoidal) waves are plotted. 



The problem now is that a realistic sea is highly irregular, with a 

 continuous probabilistic spectrum of amplitudes and frequencies . To overcome 

 this problem, we adopt the procedure, used by many other investigators, of rep- 

 resenting an irregular sea by a regular one. hi this way, we can draw some con- 

 clusions as to the chances of the success of the operation, although much depends 

 on the definition of the regular sea representing an irregular one of a specified 

 state . 



It is shown that, by attaching the above cable to the center of gravity 

 of Cuss I, the chances for the success of the operation are quite good in seas 

 excited by a wind velocity up to 25 knots (beginning of sea state 6). It is also 

 shown that, when the cable is attached to the side of Cuss 1 through a boom, the 

 chances of success can be acceptable only in very small wind velocities. 



The above results lead one to the idea of using either an unconventional 

 vessel or a lowering platform detached from the main vessel, in order to achieve 

 higher stability. The use of a very stable platform for lowering arrays into deep 

 water will be investigated further and discussed in a later report. 



artbur B3iittU3nc. 



S-7001-0307 



