approximately the size of a large aircraft carrier. The draft of these 

 tankers when loaded varies from 32 to 92 feet, depending on their size. 

 Sixteen knots is the standard speed. 



Offshore moorings are used in two different situations: (1) near 

 an offshore platform to transfer oil from the well to tankers, or (2) 

 near shore to transfer oil from tankers to an onshore terminal. The 

 technology of offshore moorings is rapidly advancing. At present, the 

 most favored type is a floating device secured by a number of anchors so 

 that a tanker is moored at a single point and is free to rotate 360 degrees. 



Pipelines have advantages over tanker transport. Bad weather 

 conditions have little, if any, effect on a pipeline, but can disrupt 

 tanker operations, forcing costly delays. The chances of a spill due to 

 human error and mechanical failure are less for a pipeline because the 

 oil flows constantly in a closed system, while tankers operate dis- 

 continuously, hooking up and then disengaging. Advanced monitoring 

 techniques to detect leaks have been used more effectively for pipelines 

 than for tanker loading systems. 



3.2.2 Site Requirements 



The optimum route for a pipeline is the shortest route between the 

 field and the shore facility, but this is not always possible from an 

 engineering standpoint. The depth and shape of the ocean bottom are the 

 major factors in laying out the system because pipeline corridors must 

 avoid deep trenches and rugged terrain. Bottom sediments and currents 

 also affect the design. Because USGS may require that pipelines on bottoms 

 shallower than 200 feet be buried, the routes usually will not cross hard 

 bottoms, nor can pipelines make landfall at sea cliffs. Geologic hazards, 

 such as active faults or areas of sediment slumping, can also cause detour- 

 ing of the corridor route. The route should also avoid major interference 

 with commercial fishing, shipping, and naval operations. The major require- 

 ments for anchored offshore tanker mooring buoys are: (1) suitable bottom 

 for anchoring and (2) favorable logistics. 



3.2.3 Potential Sources of Disturbance 



Two ecological problem areas of great concern are benthic (bottom) 

 habitat disruption and oil spills. Benthic habitat disruption occurs in 

 the process of laying pipelines, particularly in the shallower coastal 

 waters where the pipeline is laid under the bottom by a "bury barge" which 

 both digs the trench and lays the pipe. Oil spills may occur anywhere 

 along the transport route because of pipeline rupture, tanker accidents, 

 and routine tanker operations such as discharge of bilge washings. Human 

 error during transport and transfer operations appears to be a major 

 cause of oil spills. 



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