1 



82 



by a crane from the vessel on which the RCV is operated. The lowering procedure 

 stops before the blocks reach the bottom, and the RCV is used to check the height 

 of the block above the seabed to assure that there is sufficient clearance 

 for the block to be placed over the pipe. The RCV is then landed on the pipe 

 and provides a visual reference as the crane rotates to bring the block exactly 

 above the pipe. A diver is used to align the block to the pipe and the crane 

 driver, who uses a monitor in his cabin, only need lower the block from the 

 picture in front of him without requiring orders from a third party. With a 

 slightly different design of the block it is felt that this task can be performed 

 without divers . 



3.1.3 Survey 



Surveying can consist of merely observing the bottom through TV or, in addition, 

 mapping the bottom and sub-bottom acoustically with an echo sounder, side scan 

 sonar or sub-bottom profiler. Such operations are conducted to survey pipelines 

 or cable routes or sites for emplantment of structures. In some instances, 

 such as pipe trench profiling, the survey is conducted subsequent to the 

 excavation of a trench to assure that it meets specifications. 



In some instances the ROV is utilized to confirm results obtained through 

 conventional surface-oriented surveying techniques. Michel (1978) reported 

 using the RCV- 225 (during installation of the Cognac jacket base section described 

 earlier) to perform a complete bottom survey prior to setting the JBS. A 

 survey ship previously ran grid patterns over the area with towed side scan 

 sonar. Taylor Diving's RCV- 225 was subsequently used to make a complete 

 visual check of the area in case items protruding from the bottom had been 

 overlooked. 



Peterson (1978) of Martech International reports similar utilization of their 

 RCV-225 in the Gulf of Mexico where the RCV was used to inspect the bottom 

 before a drilling platform was launched. The purpose was to look for depressions 

 or obstructions that would prevent the platform from sitting level. Once the 

 platform was set, it was inspected to see if it was level on the sea floor. 

 In another instance a platform was set in 130m (425 ft) of water. The RCV 

 was used to locate level bottom and the correct depth of water, since the 

 original site was too shallow. The RCV searched for the correct depth as the 

 barge was moved to deeper water. 



In the previous section (3.1.2.b) Martech International's utilization of the 

 RCV-225 in the Garoupa field for structure alignment/orientation checks was 

 described. The vehicle was also used to conduct bottom surveys during this 

 operation. Each time the derrick barge (which laid the manifold) was positioned 

 a bottom survey was conducted. Visibility at the 112m (358 ft) water depth 

 was in excess of 60m (197 ft) during daylight hours. The RCV-225 was guided 

 to target center by tracking it with a Honeywell RS-7 positioning system. 

 Two acoustic tracking beacons were used, one on the remote vehicle and the 

 other on the vehicle deployment cage. The remote vehicle deployment winch 

 system was mounted on the port side of the barge approximately 12m (39 ft) 

 aft of the bow, thus remote vehicle travel to target center was about 30 to 

 80m (98 to 263 ft) depending on bottom current conditions during the mission. 



