Table II. Cable weight and area contributing to the time constant of a 

 current meter suspended on 3/l6-inch wire rope. 



Length, ft 100 300 1,000 



Weight lower l/3 of cable, lbs 1.6 Ik 9 16.3 

 Area lower 1/3 of cable, ft 2 0.5 1.6 I4..7 



3,000 10,000 

 1+9 163 

 15.6 1+6.8 



;LJ* 



FIGURE 1 (b). PLATFORM ANCHORED 

 IN DEEP WATER, SCOPE 1.1:1 



REGION OF ELASTIC 

 RESTRAINT ON PLATFORM 

 600 + 252 ft. 



RADIUS OF UNRESTRICTED 

 MOTION, 600 ft. 



FIGURE 1 (a). PLATFORM ANCHORED 

 IN SHALLOW WATER, SCOPE 3:1 



Fig. 1. 



REGION OF ELASTIC 

 RESTRAINT, 600 + 2750 ft 



Conventional mooring features of surface vessel platform 



RADIUS OF UNRESTRICTED 

 MOTION, 600 ft 



Effect of Elasticity and Slack in the Mooring 



The mooring inevitably has elasticity; often 

 by design in order to absorb shock loadings. 

 When the mooring line is heavier than water the 

 elasticity is in the catenary. If the line is 

 synthetic fiber rope it is mostly in the elas- 

 ticity of the material. Typical situations are 

 shown in Figs. 1, 2 and 3 for h types of mooring: 

 (l) a ship or buoy anchored in 300 feet at a 

 scope (ratio of line length to depth) of 3:1 

 shown in Fig. l(a), (2) a surface platform in 

 6,000 feet of water at a scope of l.l/l shown 

 in Fig. l(b), (3) conventional taut-wire moor 

 in the same depth (Fig. 2) and (k) the taut- 

 rope moor now being used by W. S. Richardson 

 at Woods Hole Oceanographic Institution (Fig. 3)- 

 The diagrams for the first two are self- 

 explanatory. 



In the taut-wire moor, the deviation of the 

 submerged buoy will vary with the constants of 

 the system. The wire angle has been estimated 

 at 1° for a buoy of 500 pounds net lift and 



12 square feet cross-section on 3/l6-inch wire 

 rope at an assumed velocity of 0.5 fps when negli- 

 gible drag is contributed by the surface float. 

 This is a conservative assumption since it is 

 often difficult to keep the drag of the surface 

 float as small as that of the submerged float. 

 Actual knowledge of the instantaneous velocities 

 at 150 feet depth is sparse indeed. Frequently 

 at some locations, and perhaps occasionally in 

 many, the velocity certainly will exceed 0.5 fps. 

 The degree of restraint on the motion of the sur- 

 face float with respect to the buoy depends upon 

 whether or not the upper mooring line is heavier 

 or lighter than water. If distinctly heavier, a 

 catenary forms and there is a corresponding 

 restraint shortly after the surface platform moves 

 away from vertical alignment with the submerged 

 buoy. If the line is nearly neutrally buoyant 

 there is little restraint until it is stretched 

 taut. 



To obtain a feeling for the kind of distortion 

 in the measured current due to slack and elasti- 

 city, the simple case of a purely sinusoidal 



114-0 



