UFC 4-159-03
3 October 2005
the "Z" direction at the vessel keel. A global coordinate system for the entire spread
mooring design is selected with the point (0,0,0) defined to be at a specific location. For
this example, the origin is selected to be in the middle of the vessel nest and 164 feet
(50 meters) aft of the stern of the vessels. The origin for the "Z" direction in the global
coordinate system is at the waterline. This global coordinate system is used by the
various analysis programs to define the "chain daylight" locations and the location of the
vessel center of gravity within the spread mooring footprint.
8-4.7
Number of Mooring Legs. It is estimated that eight 2.75-inch chain
mooring legs are required, based on the safe working load of the chain (289 kips or 1.29
E6 newtons) and the applied environmental forces and moments on the nest of ships.
Four legs are situated on both sides of the nest and each mooring leg is angled to be
effective in resisting the longitudinal wind forces, as well as lateral wind forces and
moments, from winds approaching at angles other than broadside. Legs are also
placed toward the ends of the nest to be effective in resisting the yaw moment. To help
control ship motions, two 20-kip (9000-kg) sinkers are placed on each mooring leg
approximately midway between the vessel attachment point and the predicted chain
daylight location. A schematic of the planned spread mooring arrangement is shown in
Figure 8-14.
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