Catenary support buoys should be manufactured from A-212 

 normalized steel plate, with internal structural members and ribs fabricated 

 from A-36 silicone steel. The buoys' surfaces must be coated for protection 

 from corrosion. The buoys should be provided with leak detectors having an 

 alarm circuit connected to the surface plant alarm system. Automatic bilge 

 pumps operated from batteries should be provided for support buoys. A 

 circumferential pipe structure should be provided to protect the buoys from 

 collision by ocean vessels. Navigational lights on suitable masts would be 

 required. 



Analysis of Surface Plant Mooring System. The sizing of mooring 

 systems for the surface plant is determined by the mooring leg holding force 

 required. Computed component drag forces for each power level at the 

 selected depths are shown in Table 9. Wind and drag forces were combined 

 into a total drag force for each condition. The required mooring leg holding 

 power of 150,000 pounds was assumed. The difference between maximum 

 holding power and the total drag force represents the wave force allowance. 

 The ratio of wave force allowance to maximum holding power was established 

 at 0.6 for the smallest hull-power-depth combination and 0.15 for the largest. 



Once the required holding power of 150,000 pounds has been 

 assumed, it is possible to trigonometrically compute the limiting angle and 

 magnitude of the vertical component of force for standard wire rope sizes. 

 A vertical component of force at any point in a catenary is equal to the total 

 weight of the leg suspended beneath it. Thus, a smaller wire rope is required 

 to support the leg below any given point. Use of a larger wire rope size for 

 the entire length of the rope will increase the scope required. 



In a compound catenary arrangment, the size of the mooring legs 

 was determined by establishing nomographs and alignment charts to provide 

 data which would otherwise be obtained from trial and error solutions. 



It is characteristic of the catenary that for mooring legs of equal 

 weight and bottom angle, the angle at the top will remain constant regardless 

 of weight distribution along its length. The weight distribution will affect 

 the scope, and accumulating leg weight into a clump will significantly change 

 the scope. From a cost effective standpoint, wire rope at $5 per foot can be 

 replaced with equivalent clump weight worth $0.35 per foot for developing 

 the same holding power. The clump weight is limited by the capacity of the 

 deploying winch and by the vertical force component of the wire rope tension. 



A typical anchor-chain-clump configuration was elected for the 

 bottom of each mooring leg based on the required holding power. It is com- 

 prised of a 25,000-pound LWT wedge block anchor, one shot of 1-1/2-inch 

 chain, a clump ranging from 25 to 100 kips, two additional shots of 1-1/2- 

 inch chain, and a scope of wire rope. 



47 



