In handling the installation over-the-side, it is preferable to 

 use as short a suspension length as possible with sufficient vertical 

 clearance to get the installation over the side rails. Articulated 

 hydraulic booms are very effective. It is also necessary to have 

 sufficient reach to prevent the installation's swinging into the side 

 of the ship. A factor of safety in the handling system of at least 

 8 relative to the dry weight of the installation is necessary. The 

 handling of the installation over-the-side should be as quick and 

 smooth an operation as possible to prevent damage. The water will 

 quickly damp out any swinging motion. Once in the water the installa- 

 tion should be quickly lowered well below the surface, to a depth of 

 50 feet or deeper if possible, to reduce dynamic line tensions and to 

 prevent unanticipated pick-up of the installation with trapped water 

 resulting from the ship's motion. Such a pick-up can cause severe 

 loading on handling equipment. Installations should be designed to 

 trap a minimum of water as it is sometimes necessary to recover them 

 with the placement equipment. For installations with large vertically 

 projected area, relative to their maximum laterally projected area, it 

 is sometimes desirable to handle these through the sea-air interface 

 on their side in order to reduce the large drag forces induced by 

 ship's motion. 



Installations are often handled over-the-side with one handling 

 system and then transferred to a winch system for lowering to the 

 bottom. This generally cuts down on the complexity of on-deck rigging 

 and control, and induced line stress from ship's motion. This transfer 

 of load can be made remotely or by divers working at depths to 70 feet 

 (deeper is possible). For deep water deployments, synthetic lines offer 

 the capability to handle shock loadings and have the advantage of lower 

 line loads, partially due to very low in-water weight of payed out line. 

 Typically they also lessen the possibility of line entanglement with the 

 installation after release on the seafloor. 



The maximum lowering rate available from many pieces of deck equip- 

 ment is about 2 feet per second. This can be too fast for many 

 installations since the lowering rate cannot exceed their free-fall 

 velocity. If it were exceeded, this could result in the installations 

 becoming entangled in the lowering line or other complications. A rough 

 rule for maximum lowering rate is as follows : 



V (feet per second) = 1/4 v/W , (pounds) + A (square feet) (15) 

 max v sub v 



On rougher days when ship's motion is significant, the rate should be 



reduced below the calculated V m „ . 



max 

 As an installation is lowered, its lateral position will be subject 



to some excursion relative to the ship's position. Assuming that the 



ship is maintaining station or attempting to do so, the maximum possible 



15 



