80 



to ensure, for example, that a skirt pile sleeve is full. At times the ROV 

 can perform other tasks than monitoring during grouting operations. 

 Peterson (1978) reported an unusual application of RCV-225 during installation 

 of a 20cm (8 in) grouting pipe through a skirt pile from to 116m (380 ft) 

 in a Gulf of Mexico structure. The original lines had become plugged and 

 the new line had to be positioned between the bell guide and the skirt pile. 

 The weight of the pipe caused it to hang just outside of the bell guide. 

 Pushing on the pipe with the RCV-225 caused the pipe to swing and the moment 

 it was in position over the bell guide it was lowered. This application 

 avoided shutting down operations in order to mobilize a diving bell system. 



3. 1.2. a Piling Installation (D. Michel, 1978, Taylor Diving Co.) 



The following description is taken directly from the above reference and 

 describes the application of one of Taylor Diving's RCV-225s during installation 

 of the Cognac platform in 309m (1,015 ft) water depth in the Gulf of Mexico. 



"One area in which RCV visual information was particularly useful was in lowering 

 and stabbing of piles. Even though sophisticated acoustic devices gave precise 

 positioning and rate of closing information to the operators, visual contact 

 with the 70- ton pile closing on the bell guide made the project a lot easier. 

 As the pile, held by the elevator, was lowered, the RCV was moved up to the 

 elevator to determine proper attitude and assure personnel that winches were 

 synchronized. Then it was moved back to the bell guide to assist in the final 

 line-up and stabbing. 



Once each pile was stabbed, a pile hammer developing more than 500,000 ft/lbs 

 of force was used to drive it into the sea floor. This was a very critical 

 stage and presented another important task for the RCV. Proper slack had 

 to be maintained in two six-inch diameter hoses supplying air and two cables 

 lowering the hammer. This was accomplished by constant visual check with 

 the RCV. A second assignment performed was monitoring depth to which the 

 pile had been driven." 



3.1.2.b Structure Alignment/Orientation Checks 



There are a wide variety of tasks which ROVs conduct within this category. 

 The following represent two of the more sophisticated endeavors. 



In 1978 Martech International's RCV-225 was used during installation of 

 Petrobras' subsea production system in the Garoupa field offshore Brazil. 

 Martech 's portion of the work was conducted in conjunction with an RS-7 

 (Honeywell) Positioning System to position and inspect the system's Manifold 

 Center (MC) . The vehicle performed a number of survey tasks during this 

 operation, the following are those tasks falling into the category of monitoring: 



-Confirmation that MC hydraulic umbilical was intact throughout the 



operation. 

 -Confirmation that lowering lines and orientation lines were free from 



entanglement during swingdown and positioning operations. 

 -Inspection and observation of the MC above the sea floor, including 



depth measurement just prior to final azimuthal rotation and lowering 



to sea floor. 



