The basic formulas used for wind and current are similar, but because 

 of the higher specific gravity for water, the forces induced by even the slowest 

 currents are significant. Surface plant hulls, which were established as sym- 

 metrical, exhibit an optimum aspect to any direction of the ocean current. 



The wave forces that act on a moored surface hull fluctuate and are 

 caused by three characteristics of a wave. First, the oncoming wave heave 

 the hull upward. Second, the wave causes the hull to slide down its slope. 

 Third, the wave subjects the hull to the increased velocity of the water 

 caused by the orbital motion as the wave crest forms. Wave forces are 

 periodic, causing the mooring leg and anchor system to react very much like 

 a weight on a spring. The problem of analyzing the transitory force on the 

 mooring leg when disturbed by the wave force is complex, and any solution 

 is peculiar to a given sea-air condition. The possible conditions which may 

 exist are infinite. For this reason, wave forces are usually neglected when 

 moors are designed, but a sufficient safety factor is allowed for environmental 

 conditions. 



Anchor Holding Power. A fluke-shaped anchor was selected for use 

 with the mooring system. The important parameter in the shape of the fluke 

 is the moment of the fluke about the trunnion. The greater the first moment 

 of the fluke area, the greater the anchor's holding power. 



The maximum angle which the fluke makes with the shanks affects 

 the holding power of an anchor in any type of ocean bottom. The optimum 

 fluke angle is not the same for all types of bottom. Past tests have indicated 

 that maximum holding power is attained in a mud bottom when the fluke 

 angle is approximately 50 degrees, whereas in a sand bottom the optimum 

 angle would be about 26 degrees. Figure 1 1 illustrates the effects of fluke 

 angle on the holding power of an anchor. 



The maximum anchor holding power is also developed when the pull 

 extended is parallel to the bottom. If the anchor end of the mooring leg 

 rises so that the angle of pull (that is, the angle of the mooring leg tangent at 

 the anchor) begins to exceed critical values, the flukes of the anchor tend to 

 break out of the bottom. Figure 12 illustrates the effect of the angle of pull 

 on the anchor's holding power. A few hundred feet of chain and a clump 

 are generally attached to the anchor shank to help hold it on the bottom 

 and maintain the desired shank angle. Figure 13 illustrates the effect of 

 anchor drag upon holding power. 



Mooring System Hardware. Conventional anchors are established 

 pieces of hardware with proven reliability. Table 8 gives the holding power 

 and weights of various conventional anchors. Development work is currently 

 progressing to create new and better anchors. In the past, anchors have been 

 pulled over the bottom to make them dig in; however, this method may not 



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