width was taken as 3/8. 



The low efficiencies and large sizes of the DORIS compared to the 

 fluke and pick type anchors previously discussed, seem to rule out this 

 choice for OTEC applications. For example, assuming it could be fabri- 

 cated, a 455 Mg (1,000,000 lb) mud anchor would be required to equal the 

 capacity of a 136 Mg to 182 Mg (300 to 400,000 lbs) fluke type anchor, 

 and the large size, at least 36 m (118 ft) long, 33 m (107 ft) wide and 

 12 m (40 ft) high, would make the mud anchor extremely difficult to 

 handle and deploy. 



Anchor Fabrication 



The limiting criterion regarding conventional anchor use in OTEC is 

 fabrication capability. Two methods are available with which to fabri- 

 cate these anchors, welding and casting. 



The feasible construction limit for a welded anchor, without resort- 

 ing to costly built up section, depends upon available steel. Heat 

 treated steels of 760 MPa to 1100 MPa (110 to 160 ksi) strengths in 

 thicknesses of .051 to 0.10 m (2 to 4 in.) can be obtained; however, the 

 complexities involved with welding these materials make them undesirable 

 choices. The most desirable steels for this application are HY-80 andA514 

 Of these, HY-80 is superior because of its superior touqhness. Thicknesses 

 of up to 0.11 m (4.5 in.) are available. This would allow a 68 Mg 

 (lbU,UU0 lbs) fluke type anchor to be fabricated. 



The feasible limit for a casting depends primarily upon the volume 

 of steel required. Available information suggests that this would trans- 

 late into approximately a 45 Mg to 64 Mg (100,000 to 140,000 lbs) maximum 

 size for a pick or fluke type anchor. The practical limit for cast steel 

 strength is 517 kPa (75 ksi). This value is almost coincident with the 

 steel used to cast the Bruce anchor. One alternative is to fabricate an 

 anchor by partial casting and welding. This would increase cost over a 

 normal casting but could also potentiallly increase practicable size. 



A significant factor in fabrication procedure is cost. For example, 

 casting large anchors (45 Mg range) requires large flask capacity and would 

 cost roughly $3.30 to $4.40 per kilogram including pattern fabrication. 

 The cost of a welded construction of this size would be $5.50 to $6.60 per 

 kilogram. The actual cost may be higher than the quoted figures because 

 there would undoubtedly be some engineering involved in fabricating these 

 large anchors. The largest anchor that has been fabricated in this 

 country is 27 Mg (60,000 lbs) (April, 1976) even though the largest 

 advertised is 45 Mg (100,000 lbs). 



Cost is not the only criterion that should be used in selecting 

 fabrication method. Fabrication and use experience are also significant. 

 There is limited experience in casting large anchors; thus, it appears 

 that there would be more uncertainty both with fabrication and in-service 

 use. Quality control of a very large casting may be difficult. Thus, 

 the lower limit of the potential range (45 Mg) is recommended for casting. 



19 



