Utility companies have been laying pipelines and cables across the ocean floor for more than a century. Prior the introduction of GPS, marking their position was a difficult and tedious task, fraught with error. It is extremely important to know the exact location of existing lines before undertaking dredging operations or when new pipes and cables are laid down.
Regulations require they be buried from several feet to several meters under the ocean bottom to prevent snagging by boat anchors and fishing trawls. This depth of burial typically makes them impossible to find with conventional metal detectors. Two pieces of equipment have proved most effective in finding them; a pinpointing magnetometer and a cable tracker. The pinpointing magnetometer is a very sensitive device that locates iron and steel pipes buried up to 16 feet in the bottom, and the cable tracker is powerful enough to detect a power or communications cable at more than 30 feet away.
One company using both instruments in their subsea operations is WJ Castle PE & Associates. Company founder William Castle has been providing marine and structural engineering services for almost 30 years, and has served on a number of industry boards including the Association of Diving Contractors (ADC). Recently Castle was subcontracted by Brayman Construction to perform an inspection and document the underwater conditions at a utility’s proposed site for a diffuser pipe extension. Using JW Fishers CT-1 cable tracker and PT-1 pipe tracker, Castle’s team of divers searched for a high voltage power cable and pipeline running through the area. Complicating the job was the excessive amount of debris littering the site including steel plates, beams, and wire rope. Also close by were a seawall constructed of steel reinforced concrete and steel plates. Very high concentrations of ferrous metal in the area prevented the use a standard magnetometer as it would be impossible to locate individual pieces. The primary advantage of the PT-1 is its ability to pinpoint targets, even in areas surrounded by steel structures. Despite the challenges, diver Greg McGrath reports they were successful in finding both the pipe and cable. The team marked the positions of both, and also determined their approximately depth of burial under the gravel bottom.
Based in Hong Kong is the BEKK Group of Companies. They offer a broad range of services in an array of fields including civil engineering, underground construction, marine engineering, and offshore oil and gas. They have worked on projects from the Middle East to the Asia-Pacific Region. Recently the company was awarded a contract to provide marine support, personnel, equipment and materials for the first phase of the offshore wind farm being built for Hong Kong Electric Company. Two of the first pieces BEKK procured to assist in this project are the Fishers PT-1 pipe tracker and Pulse 8X metal detector. Both will be instrumental during the site survey and clearing operations.
Another firm employing the CT-1 cable tracker is Denholm Offshore based in the UK. The company offers complete shallow water power and communications cabling service, including installation and maintenance. They also provide route clearance and cable recovery. Denholm is currently working on a multiple landing telecommunications installation between West Africa and Europe. Company spokesman Gary Waterman reports, “The tracker has worked very well. It’s been a great help on this project.”
Nava19 Engineering in Thailand is also having good results with the cable tracker. Owner Prajuab Riabroy reports, “We used the tracker to find a submarine power cable. It located the cable very easily, saving us time and money. On another project we induced a signal into a fiber optic cable with the Signal Injector Box. Our divers used the hand-held probe to track the cable for several kilometers. It is a good piece of equipment.”
For more information of JW Fishers complete line of underwater search systems go to www.jwfishers.com.