and screw anchor combination would then be transported and positioned as 

 a single unit. The helix would be embedded by hydraulic motors driven by 

 electric power from the surface as proposed by Raecke (1973). 



Only a single helix arrangement is considered feasible for the pro- 

 cedure suggested above. The added capacity of a multiple helix is out- 

 weighed by the complexities of installing it through the deadweight. 



Holding Capacity . The hoi ding capacity of a single helix anchor 

 can be computed using procedures identical to the plate anchor procedures 

 presented above. Approximate helix areas required may be found using 

 Figures 7, 3, and 9. The representative plate anchor sizes in Table 9 

 may also be taken as representative helix sizes. 



Embedment. The power required to embed helices of the sizes 

 suggested by Table 9 is a matter of conjecture. The screw-in anchor con- 

 cept proposed by Raecke required a 45 kW (60' hp) power source at the surface 

 to install a single-helix anchor, 0.8 m diameter, to a depth of 15 m. 

 Present offshore systems (Short, 1971) are powered by hydraulic motors 

 requiring about 56 kW (75 hp). On the basis of fluke area, or holding 

 capacity, an extrapolation of roughly 20:1 would be required for OTEC 

 helix sizes. Power requirements are probably within reach. 



Summary. 



1. Single helix anchors, used to supplement the vertical capacity 

 of a deadweight, are feasible. Further investigation should provide 

 information regarding the economic aspects of the suggested concept. 



2. Single or multiple helix anchors are not feasible as the primary 

 OTEC anchor due to low lateral load-capacity. 



3. Multiple-helix anchors do not appear suitable for use with 

 deadweight because of installation complexities. 



PILE ANCHORS 



The evaluation of piles as OTEC anchors first considered a single 

 pile, unrestrained head, subjected to a slowly applied horizontal and 

 vertical load (Figure 17). Lateral and axial (pullout) capacities were 

 determined for soil categories A, B, C, and D. Behavior of piles 

 subjected to repetitive loading was estimated using available guidelines. 



Pile Lateral Capacity 



The effect of soil strength, pile length, and pile diameter on 

 lateral capacity was determined by combining the results of a short and a 

 long pile analysis. Overlap of the two procedures at a transition length 

 (10 x diameter) allowed some comparison of results. Comparisons for piles 

 of a given diameter were made c or similar pile stiffnesses. 



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