requirement that mild steel be used for fabrication caused plate thickness 

 to increase as about w''^ for the larger sizes. For purposes of this 

 evaluation, the 5.5 Mg (12,000 lb) STATO, which exhibits efficiencies 

 at maximum drags of 25/1 in soft clay and 35/1 in sand, will be used as 

 the basis for this extrapolation. The lattter value was controlled by 

 steel stress rather than soil strength. 



Geometric similarity is maintained by increasing steel strengths as 

 well as the linear dimensions in proportion to WV3. Characteristics 

 of the scaled-up anchors are given in Table 2. Anchor weights required 

 to produce these capacities are shown in Figure 4. The required weight in 

 the lower capacities is dependent upon soil strength; wehreas, anchor 

 steel stress controls weight in the larger capacities. It is appparent 

 from Figure 4 that once the criterion of limiting steel stress is achieved, 

 anchoring efficiency no longer remains constant. Data from tests on 

 existing anchors indicate that holding capacity increases in proportion 

 to W*"9. This is extremely close to the theoretical limit of W . This 

 slight difference is atrributed to errors in transferring data from log-log 

 plots of actual steel stress versus anchor weight. Based upon this behav- 

 ior, the most efficientanchor occurs at the intersection of the curves 

 plotted for soil type and steel yield stress. 



Another anchor, included in this category but somewhat different 

 than the movable fluke type previously extrapolated, is the BOSS anchor, 

 a fixed solid fluked anchor. Existing data show this to be a very 

 efficient anchor in small sizes; however, there was insufficient data to 

 confidently extrapolate performance. A conservative approximation of 

 holding capacity was thus proposed. 



R - 610 W 75 (1) 



where R = holding capacity (N) 



W = weight (N) 



The exponent ".75" was recommended by Cole and Beck, 1969. The extremely 

 high efficiencies in the small sizes is attributed to the thin, high 

 strength sections used in the anchor. Without modifying the design by 

 adding stiffeners on the flukes, the practical limit of this design, 

 maintaining geometric similarity, is probably much less than 45 Mg 

 (100,000 lbs). By adding stiffeners to this anchor, the performance 

 should more closely resemble STATO type designs since fluke/shank angles 

 and effective fluke areas are approximately similar. A primary advantage 

 of the BOSS anchor is its ability to embed in competent seafloors, a 

 problem often encountered with other fluked anchors. The technique of 

 fixing the fluke on one side of the shank may be appropriate for the 

 movable fluke anchors, if they are used in competent seafloors. 



A pertinent characteristic of the enlarged fluke anchors is their 

 expected penetration depth. This information is needed to enable design 

 of the anchor pendant in contact with the seafloor and provide an idea of 

 how much lateral movement is necessary to fully set the anchor. A 

 reasonable approximation in clay is that the setting distance to achieve 

 peak capacity is six times penetration depth. For example, penetration 



