0.5 inch (0.043 ft). A motor driven pivot arm and cable were used 

 to pull the slider arm up. Negator springs were used to pull the 

 arm down. The frequency of motion was variable from 0.1 to 2.2 hertz. 



The experimental conditions for the five model mooring lines are 

 given in Table 3. Listed are the model material, anchoring configura- 

 tion, water depth spanned, mooring line length, scope, motion amplitude, 

 current speed, and the preset trail (horizontal displacement (v)) 

 between the upper and lower ends of the mooring line. The upper-end 

 termination was mounted on a movable carriage which allowed horizon- 

 tal displacement to be varied. The mooring line lengths were select- 

 ed to correspond to the typical full scale scopes of 1.1 and 1.3 

 illustrated in Fiqure 1, except for the case of the weighted nylon 

 cord which exceeded these values. The length of the nylon line was 

 computed rather than measured directly. In water, nylon parachute 

 cord normally shrinks. However, in this case, the shrinking nylon 

 tended to neck down between the lead balls used to weight the line, 

 which resulted in their being pushed apart. This extended the line 

 1.25 percent over its dry length. Also, the nylon cord exhibited 

 an elastic coefficient (spring constant of a unit length under load) 

 of 36.5 pounds. These two factors together with ihe average dynamic 

 tension value were used to compute the "stretched" length from the 

 measured dry length. 



With respect to the anchoring configuration, fixed-pivot or "excess 

 line on-the-bottom" cases are indicated. For "excess on-the-bottom" 

 cases, a referen j was established at the specified line length and 

 this reference was set just tangent to the channel floor under steady 

 conditions. The current speeds were and 0.6 knots. The preset 

 horizontal displacement positions were established from previous exper- 

 iments and from the calculation of conditions where the steady hori- 

 zontal force-component at the top would be 0.25 and 0.5 times the 

 weight in water of the mooring line. The resulting steady loads, 

 however, deviated from these desired loads and ranged from 0.05 

 to 0.85 times the weight in water. 



11 



