Divers and ROVs partner up for smoother inland operations
By Nick Fortuna
The video shows a juvenile octopus crawling sideways on the bottom of Northumberland Channel, making a beeline for the ROV’s manipulator. The tiny mollusk moves with purpose, stops right underneath the manipulator, senses sudden movement and scampers off. It’s almost as though it wanted to help the manipulator grab a lift sling resting on the bed but was rebuffed.
You can’t blame the octopus for being curious after stumbling upon a pretty cool scene last February. Global Diving and Salvage was rigging the Samantha J for recovery, more than four years after the 35-foot-long steel-hull tugboat had sank near Nanaimo, British Columbia. The tugboat had run into trouble while towing a woodchip barge, and though no one was hurt, the vessel was lost, sinking 230 feet below the surface.
Toward the end of the two-day recovery project, the team stabilized the Samantha J on the deck of the Arctic Tuk, a 600-ton derrick crane barge, and defueled it, collecting 1,436 gallons of fuel oil, engine oil and hydraulic oil and 8,617 gallons of oily water. The Canadian Coast Guard then inspected the Samantha J before it was returned to its owner and refloated, capping another successful simultaneous operation using both divers and ROVs.
Salvage operations and facility inspections are among the most common simultaneous operations involving divers and ROVs, said Warren Posten, ROV supervisor for Global Diving. The specific roles for each may differ depending on the project, but together, they form a highly effective team.
“In this particular situation, it was the diver supporting the ROV, but in other situations, we’ve got the ROV supporting the diver,” Posten said. “The safety of the divers is top of mind at all times, and the equipment is second. Any time a diver is working around rigging or doing construction, it’s important to have that second set of eyes on location to conserve bottom time and increase safety.”
A big lift in two stages
Jones Marine Services, which owns the Samantha J, wanted its vessel salvaged, but that wasn’t why the Canadian Coast Guard had ordered its recovery. There were recurring oil slicks at the wreck site, and the sunken vessel posed a navigation hazard because it was sitting on the edge of an anchorage site at the Port of Nanaimo.
To get started, the Arctic Tuk set up its mooring anchors at the wreck site, and the area was boomed off to contain any oil that might be released during rigging and lifting. Global Diving lowered the clump weight of its Saab Seaeye Cougar work-class ROV to within three feet of the tugboat’s pilot house. The crew used the ROV to inspect the wreck site, checking for rigging clearances and debris, and discovered ropes and lines that presented a navigation hazard for the ROV.
Global Diving’s team adjusted the preliminary rigging plan and lowered the chain and lift sling to be set by the ROV. One section of chain was rigged to the bow, and then the ROV positioned the two-point sling just in front of the rudders. The ROV’s manipulators threaded a messenger line connected to the chain through the pick points while the team continuously adjusted the chain and repositioned the ROV to work around the tugboat.
On Day 2, the ROV performed a preliminary inspection of the bridle and all the rigging to confirm that it hadn’t fouled overnight. The barge team then slowly brought up the chain until all slack was out of the rigging. With everything in position, the team started to lift the Samantha J. The maximum pull was 97,000 pounds of force to break the vessel free from the bottom; once free, the in-water weight was 68,000 pounds. As the crew raised the vessel, the ROV monitored their progress until the bridle broke the surface.
To prepare the vessel for the final lift out of the water, divers rigged the derrick crane’s chains around the wreck, transferring the load from the ROV’s sling to the crane, then removed the ROV’s rigging. The crane raised the tugboat to deck level, and after the vessel was mostly dewatered, the crane performed the 150,000-pound pick and set the tugboat down onto the barge deck.
Working as a team
Posten said collaboration between the divers, dive supervisor and ROV supervisor was essential.
“We had to maintain separation between the diver and the ROV’s tether and try to keep the diver out of the thruster wash of the ROV,” he said. “We were using the ROV to watch the diver the whole time he was rigging. If we saw that he was having a little trouble, we’d have a discussion and the ROV would go in and assist—maybe grab a sling and give it a little tug so it can be pulled up to where the diver can reach it before he puts a shackle on the four-point bridle to lift the tug out.”
Rodney Grounds, harbor master at the Port of Nanaimo, told the Nanaimo News Bulletin that the wreck had rendered the anchorage site useless, but thanks to Global Diving, “Now, I can put a 225-meter ship back in there.”
Even if an ROV isn’t using its manipulators, it can be an invaluable tool to foster diver safety on salvage projects. Moran Environmental Recovery recently used an ROV to confirm that a sunken vessel was sitting on its hull before it was picked, dewatered and refloated. If a vessel is resting on its side, for example, a diver would need to hook up the rigging in such a way that when the crane comes up on the rigging, it will roll the vessel, putting its hull on the bottom.
“We would never move the vessel with a diver in the water, so with an ROV, you can keep an eye on what’s going on down there while you’re moving a vessel, and that can dictate your crane ops,” said Richard Coley, Southeast business manager for MER’s commercial diving division. “When you see that the wreck is sitting nice and flat and looks stable, then you can send the diver down to reorientate the rigging so we can do a four-point pick.”
Promoting diver safety
Randy Jacobs, director of the dive group for J.F. Brennan Co. Inc., said his company typically uses ROVs on inspection jobs to ensure that conditions are safe for divers before they enter the water. A leaking sluice gate or an open valve at a wastewater treatment facility or power plant could lead to a potentially deadly hazard such as differential pressure, or Delta P—a situation where the pressures between two bodies of water are dramatically different.
Jacobs said his team will mount flow meters onto the ROV to monitor the direction and strength of water flow and will use pieces of yarn to detect when the ROV is nearing a leak or other hazard. If an ROV pilot notices sediment being sucked through an opening, that is an immediate cause for concern, Jacobs said.
“Many times, if you have a gate or a valve that’s leaking, it looks a lot worse from the surface than it actually is, but you still don’t want to take the chance of putting a diver down there, so we’ll put the ROV in and verify that it can actually fly against it and that it’s not a danger to the diver,” he said.
ROVs’ high-definition cameras are used to identify safety issues during inspections and construction projects, including areas of broken concrete or excessive corrosion, Jacobs said. When repairing concrete on the upstream side of a hydroelectric dam, for example, it’s necessary to close all the gates and isolate that area. But any number of issues can prevent that from happening, including bent or broken valve stems, faulty seals, broken valve guides or a gate coming down on a rock or debris.
In areas with clear visibility, the ROV can provide a visual picture of the structure to be repaired and the overall work setting before the diver and his gear enter the water, potentially kicking up sediment and debris that can limit visibility.
“Before you can decide what you’re going to do, you need to see what the malfunction is, so we would put an ROV in to get eyes on the situation,” Jacobs said. “Of course, if the ROV gets sucked into the gate, it’s not a good thing, but it’s a lot better than having a diver sucked in there and trapped. We like to be able to look at the situation and kind of get the lay of the land before we put a diver in.”
The HD cameras also are useful for inspecting long pipes, especially since smaller ROVs can fit into pipes that divers can’t, Jacobs said. The diver will take the ROV down to the opening of the pipe, launch it and tend the ROV’s tether, allowing it to go several thousand feet into the pipe, he said.
Addressing key concerns
Clear communication between team members and an awareness of both the diver’s umbilical and the ROV’s tether are among the keys to conducting simultaneous operations safely, Coley said.
“You don’t want to create a hazard for the diver by fouling up an ROV on a life-support component such as an umbilical,” he said. “If you needed to get the diver out in an emergency, you wouldn’t want that to be a hazard, so you have to keep that in mind and stay clear of the diver and make sure you have a tight tend on the ROV.”
To reduce chatter and eliminate confusion, the dive supervisor should be the sole point of contact for the diver and the ROV team during simultaneous operations, Jacobs said. Further, if the vessel’s captain wants to rotate his heading, he should check with the dive supervisor first to make sure it’s safe to do so.
“Basically, he’s kind of like a clearinghouse for all the information coming through,” he said. “You want one guy to be giving the commands. The dive supervisor should always know where the diver is and where the ROV is. Ultimately, it’s up to him as far as when and how to give the command.”
Clear communication is essential in both inland and offshore simultaneous operations. In late November, Mike Van Fleet, offshore manager for Oceaneering, was staring at two screens aboard a saturation diving support vessel in the Gulf of Mexico, where a diver and an ROV were working in tandem to cut up piping and rig it for salvage. The ROV was equipped with thruster guards to prevent it from sucking in the diver’s hose.
A 166-pound diamond wire saw was outfitted with a 75-pound float to make it easier for the diver to place it onto a section of pipe to be cut. Before the ROV used hydraulic power to cut the pipe, the diver would retreat to the clump weight below the saturation diving bell for safe haven. The ROV pilot could tell by the pressure on the saw blade when the cut had been completed, and the diver would then return to the ROV to reposition the saw again.
“Communication is the No. 1 thing, and it all goes through the dive supervisor, who’s talking directly to the diver and the ROV pilot,” Van Fleet said. “The diver has priority, and the ROV is not allowed to move unless the diver is in a safe spot. If the vessel captain wants to move the boat, he goes to the dive supervisor to ask if it’s safe. You just want to be sure that everyone knows the communication chain.”