Over 5,600 derelict fishing nets had been removed from Puget Sound water by volunteer divers from depths up to 105 feet. Yet there remains many more in deeper water. Global Diving,working with Natural Resources Consultants for the Northwest Straits Foundation developed custom tooling and a ‘plan’ to remove the nets using a SAAB Cougar and Falcon ROV. First the ROV’s surveyed the nets,then a plan was developed,utilizing the tooling to gather and cut the nets free from the obstacles they snagged on. Once gathered and free,they were connected to the line from a vessel mounted crane. The balls of net were raised to the surface for proper disposal.
This pilot program was developed to test the feasibility and develop the tools and methods required for this removal.
Global’s Cougar and Falcon ROV systems were mobilized to Hawaii to facilitate repairs on the 40” coldwater pipeline transition section in 500 feet of water off of Keahole Point on the island of Hawaii for the Natural Energy Laboratory of Hawaii Authority (NELHA).
The 40” pipeline is unique in the fact that it is installed with gravity anchors to a depth of 457 feet and from there to a depth of 2000 feet it takes the form of an inverted floating catenary. An installation error when the pipeline was originally installed in 1987 led to future failures of chain bridals and anchor chains. In addition growth on the pipeline was weighing it down.
The ROV crew,operating off of the Healy Tibbitts 544 crane barge,was tasked with restoring the pipeline to an as designed condition. The Cougar ROV cut loose and replaced two 500 foot 1-1/2” stud link restraining chain bridals. The pipe had to be cleaned and obstructions cut loose for the installation of new pipe clamps in three places. 1-1/2 tons of flotation was added at each clamp location. Two 1-1/2” stud link chain bridals were added at the bottoms of the clamps and secured to a 40 ton gravity anchor. A 1-5/8”stud link chain bridal was added to the offshore bridal. Special underwater tooling was designed and manufactured including a hydraulic chain tensioner,3-1/2 and 10 ton winches and 40 and 48 inch hydraulic actuated pipe clamps that were tested in Seattle before being deployed to Hawaii.