A typical approximation in the industry is to assume that a 1/2-l<not 

 current is acting on the pipe string along its entire length. Since this assump- 

 tion has proven to be a good design criterion, it appears that a stress of 

 around 6,000 psi in bending can be considered the maximum for a 

 horizontal current loading on a 600-ton load. For lighter loads, however, 

 some fairly high stresses are possible. While these are significant, they will 

 not stress the pipe beyond 70% of the yield stress (the industry's accepted 

 maximum for the total combined stress). 



Displacement of the Load 



Horizontal currents will tend to displace the load. The maximum 

 deflection, Vmax' '^ calculated by using the equation'^'' 



= — p. [j /i --lu^ - sechu) - C(tanhU - U )1 



where U = -: 

 J 



'il 



The deflections were calculated for various loads. The results are plotted in 

 Figure B-8. 



It can be seen that the load could be displaced considerable distances 

 under the influence of a 1/2-knot current. The lighter loads will be displaced 

 further than the heavier loads, in some cases over 200 feet. The distances 

 plotted in Figure B-8 are less than those which would probably be encountered 

 in an actual operation since the drag on the load was not taken into account. 



It appears that there is no practical way to avoid the problem of 

 displacement other than having some kind of guy wire arrangement. The 

 obvious solution is to have the surface support vessel upstream from the 

 foundations, although it would appear that this would be a difficult operation 

 to perform with an acceptable degree of accuracy. 



119 



