neutral position 

 of buoy 



Figure 8. Elevation view of one plane of a typical four-point moor. 



Figure 10 illustrates a three-point mooring system excursion envelope. 

 The shaded area represents the slack rope in excess of (S - Y) that can be laid 

 on the bottom. This slack would cause the wire rope to foul, kink, and 

 entangle. Accordingly, the three-point moor was not considered further in 

 the study. 



Forces Acting On Mooring System. The weight of the mooring system, 

 which increases in proportion to the anchoring holding power and the depth, 

 must be supported by the surface hull. If the hull is not large enough for 

 supporting the weight, an intermediate catenary support buoy must be used 

 to support the weight of each mooring leg segment. The support buoys must 

 withstand sea pressures at depths corresponding to the 60-foot wave height 

 expected. The forces acting upon a moored surface hull are created by wind, 

 waves, and ocean currents. Surface conditions established for the study pro- 

 gram were 150-mph winds, 10-knot currents, and 60-foot-high breaking waves. 



Wind not only applies force to the hull structure above the surface but 

 creates waves and currents as well. Model tests were conducted at the David 

 Taylor Model Basin to estimate the force on a moored hull from wind at 

 various velocities. These wind forces were extrapolated from the scale model 

 to the full-size hulls used in the study. 



40 



