magnitude of this excursion can be approximated by the following two 

 inequalities . 



For shallow water or locations of very high currents - 



, *A 



1 w 



£ 



For most other locations with water depths greater than 300 feet - 

 1 W 



* 4~ (i6) 



sub 



r £10 * A, * YT (17) 



sub 



These equations will give an approximate maximum for all cases except 

 where an oversized (from a loading standpoint) synthetic line is used. 

 Normally the excursion will be much less than the magnitudes indicated 

 above, however, these equations indicate what is possible where large 

 currents are present. 



As the installation approaches the seafloor it is necessary to 

 reduce the lowering rate by at least a factor of four. The reason is 

 to prevent impact with the bottom which can result in bearing failures. 

 A high rate of approach also causes flat footings and similarly shaped 

 installations to skate about laterally as they are lowered. This would 

 result in a foundation being landed with some lateral velocity which 

 typically causes improper emplacement, including initial inclinations 

 as large as 15 . 



Once bottom contact is made, payout of line should be ceased in 

 order to prevent entanglement, and any checks for proper emplacement 

 should be completed as quickly as possible. Then, the installation 

 should be released and the lowering line moved clear to prevent entangle- 

 ment with the installation. The means for releasing may be electro/ 

 mechanical, acoustic/mechanical, explosive, trip weight actuated, bottom 

 contact actuated, or some other. If two lines are used, one load bearing 

 and the other electrical, they should either be separated by a large 

 distance at the surface, or secured to each other with allowances made 

 for relative elasticities. Under normal circumstances two lowering lines 

 should not be used. 



If a foundation is to be recovered after deployment, it may be 

 necessary to take into account the breakout force required to remove the 

 foundation from a cohesive sediment (see Reference 21) . This force can 

 be several times larger than the installation's submerged weight even 

 when it is removed slowly. In order to reduce the magnitude of this 

 required force it is suggested that the recovery line be attached 

 eccentrically to the foundation — possibly on the edge or corner of a 

 footing. Rapid breakout by brute force should be avoided; rather, a 

 load two or three times larger than the installation's submerged weight 

 should be applied and maintained until breakout is achieved — usually a 

 matter of minutes or tens of minutes for larger installations. Breakaway 



16 





