of the potential OTEC siting zones will result in significant soil hold- 

 ing capacity reductions. This necessitates increased anchor dimensions to 

 reduce the critical stress levels. A better solution to the dynamic 

 loading problem would seem to be to reduce the dynamic stress level by 

 making the mooring more compliant by lowering the line angle. 



STANDARD BURIAL ANCHORS 

 Introduction 



Standard burial anchors are a potential choice for anchoring struc- 

 tures of the sizes projected for OTEC. These burial anchors do not exist, 

 however, in sizes large enough to yield holding capacities commensurate 

 with simplified installation and efficient use of components. Use of the 

 existing small anchors would result in \/ery difficult load equalization 

 problems. Overdesign would be required due to the high degree of uncer- 

 tainty involved in achieving load equalization. 



The largest anchor advertised available weighs 45 Mg (100,000 lbs); 

 the largest anchor tested weighs 13.6 Mg (30,000 lbs); while the largest 

 anchor tested sufficiently to yield data that could be used to extrapo- 

 late to sizes needed for OTEC was 6.8 Mg (15,000 lbs). This is a long 

 way from the anchor weight required to yield holding capacities in the 

 13.3 MN to 44.5 MN (3xl0 6 to lOxlO 6 lb) range, the range which might be 

 practicable. 



Performance Prediction for Scaled-Up Anchors 



Three basic types of burial anchors were chosen for extrapolation, 

 the standard fluked type (e.g., STAT0 DANF0RTH, BOSS), the pick type 

 (e.g., BRUCE, HOOK, ADMIRALTY MOORING) , and the mud type (e.g. DORIS, 

 PARAVANE) anchors. Using relationships between anchor weight and anchor 

 holding capacity (Valent et a!., 1976) the required weights of these 

 anchors could be determined for various soils and holding capacities. 

 Extrapolation can be accomplished only for: (1) geometrically similar 

 anchors, or (2) varying anchor geometries where the effect of variation 

 on holding capacity is known. In order to provide some measure of con- 

 fidence in the results of the extrapolation, geometric similarity will 

 be maintained. 



Fluked Type Anchor . The STAT0 configuration (similar to 0FFDRILL, 

 M00RFAST, STAYRITE) will be scaled-up because the majority of available 

 data exists for this particular anchor. Figure 3 details the character- 

 istics of the STAT0 anchor. If the existing STAT0 anchors were geometric- 

 ally similar, the efficiency of the anchor type would be constant 

 (Coombes, 1931). The data show, however, that efficiency decreases slightly 

 with size. This occurs because the linear dimensions of each anchor do 

 not vary exactly as weight to the one-third power, i.e. WV3. The 



