Dynamic Moor. A dynamic moor consists of propulsion devices 

 which will permit forces to be applied to the hull in any direction to keep it 

 in a stationary position against forces of wind and sea. The dynamic moor 

 requires an automatic sensing device which will accurately locate and hold 

 the hull with respect to the desired position on the bottom. 



A dynamic mooring system is relatively costly because of manning 

 and logistics problems, and its reliability for use with underwater power 

 systems is questionable. For these reasons the dynamic moor was not inves- 

 tigated further. As the state of the art of this mooring technique advances, a 

 reevaluation would be recommended. 



Static Moor. A static moor consists of a wire rope or chain connecting 

 the surface hull to a device on the ocean bottom which is capable of develop- 

 ing an anchoring or holding force. Several anchoring devices are available, the 

 most common of which is the fluke anchor. Three types of static mooring 

 systems were considered: the simple catenary, the taut line, and the com- 

 pound catenary. They are illustrated in Figure 7. 



The chief disadvantage of a simple catenary is the extremely long scope 

 required for great depths. On the other hand, a taut mooring line requires an 

 anchoring device capable of developing a large vertical component of force. 

 Such an anchoring device would have to be fixed to the bottom by grouting. 

 Because techniques for emplacing a fixed anchor were considered developmental 

 the taut mooring line was not considered further in the study program. 



A four-point compound catenary mooring line was selected for the 

 surface plant mooring system because it would provide reasonable scope 

 requirements and adequate holding power by means of a fluke-type anchor. 



Static Multipoint Mooring. A four-point moor may be considered as 

 a system of two 2-point moors lying in normal planes. An elevation of one 

 plane of a typical four-point moor is illustrated in Figure 8. The anchor 

 spacing would be equal to X -I- (S - Y) + 2£ and the thick-disc hull neutral 

 position equal to M2[X + (S - Y)] -i- C, where £ is the horizontal distance 

 between the hull and any intermediate cantenary support buoys. Figure 9 is 

 a plan view of the excursion boundary for a four-point moor. This envelope 

 is circumscribed by the maximum horizontal projection (X) of each mooring 

 leg. The path of the relaxed leg (S - Y) is also shown. To prevent the moor- 

 ing ropes from dragging back over themselves, X should not overlap S - Y at 

 any location. When an excursion force (F) is applied colinearly to any single 

 mooring leg, the moor is holding in its weakest condition; the strongest 

 condition occurs when an excursion force is at 45 degrees to the hull. The 

 maximum excursion for a four-point moor was determined from the equation 



6^3, = 2[X - (S-Y)] 



38 



