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same time as the other relevant data on the surface (short base, surface 

 navigation) by the first computer which provides in real time a plot 

 of the vehicle's position, thus allowing the route to be plotted point 

 by point. 



This information is then passed to the second computer which processes 

 in real time, the data from the different sensors, calibrates them, 

 corrects them, inter-relates them if necessary and finally plots them 

 in the form of curves as a function of the distance run. 



Pipeline Inspection Operation 



The support ship is positioned in the immediate vicinity over the pipeline to 

 be surveyed and launches the tethered vehicle. The vehicle is then dived to 

 the seabed and controlled via the umbilical. When in position over the pipeline 

 all systems are tested and recorders checked to ensure no malfunction. Figure 

 5.2 depicts the major system components at this point in time. 



The vehicle is now electronically locked onto the pipeline via the pipetracker 

 coupled to an automatic pilot which ensures that the vehicle follows along and 

 directly over the pipeline. The active SIMRAD short base navigation system 

 interfaced with the G.E. dynamic positioning ensures that the ship remains 

 directly over the underwater vehicle. Offsets can be fed into the system to 

 allow for umbilical drag. 



The inspection vehicle now moves along the pipeline controlling the support 

 ship where all data received from the sensors via the umbilical is being recorded 

 and processed in real time. The only endurance limitations to the system are 

 weather, maintenance and operator fatigue. To quote average pipeline distances 

 inspected per day can be misleading as distances covered will depend upon 

 conditions experienced: bottom tidal stream, rock dump areas, requirements for 

 detailed inspection of specific areas, surface sea state, debris, pipe covers 

 and all the other conditions that will affect the rate of advance. 



The content of the final report depends upon the client's requirements. It 

 usually contains, but is not limited to, the following information: 



Pipeline - geographical location 



UTM/DECCA lattice or similar 



Mile posts/KP from start 



Contractors joint number 



Scale 



Anodes 



Bathymetry /Sub-bottom profiles 



Isobathic curves 



Cautions/obstructions 



Current density - condition of anodes 



Cathodic potential 



Compass rose 



Tidal stream: surface/sub-surface 



Trenching details: top of pipe, bottom of trench, mean sea bed level 



