Mechanical Engineering Magazine - 1 Jul 08

Prof. Robert B. Laughlin
Department of Physics
Stanford University, Stanford, CA 94305
(Copied 16 Jan 10)

Robots of the Sea

A new design for ships aims to leave pests in their home waters.

By John K. Borchardt
July 1, 2008

Extended Reach: ROVs can search for oil or repair structures where it is impractical or impossible for humans to go.

In dark, ice-cold ocean depths under crushing pressures, remotely operated vehicles work around the clock. ROVs can map the sea floor, explore the ocean depths for scientists, and locate shipwrecks for archeologists. They also are extending the reach of the energy industry as it pursues oil into ever-more-difficult environments.

According to Chris Nicholson, founder of an ROV firm, Deep Sea Systems International in Falmouth, Mass., "ROVs are electromechanical equivalents of highly skilled human divers. They go where man can't go economically or physically." Still, it takes people to operate these robot workers of the deep.

DOER Marine in Alameda, Calif., is another creator of underwater ROVs. According to the company's president, Liz Taylor, "The last six years have seen major growth in homeland security applications - harbor control and vessel inspection."

ROVs are essential to the development of offshore oil and gas reserves below ocean waters 3,000 to 4,000 meters deep. They were critical in repairing heavy damage inflicted on subsea facilities after the 2005 Hurricanes Katrina and Rita.

At Transocean Inc., which bills itself as the world's largest offshore drilling company, the corporate environmental advisor, Ian Hudson, estimates that there is a large population of ROVs at work. "At any one time, there may be hundreds of ROVs working on drilling rigs and vessels all over the world, from shallow coastal waters to waters over 3,000 meters deep," he said.

Arm of the Sea: Engineers for the U.S. National Oceanographic and Atmospheric Administration work on a manipulator arm aboard the Ship Okeanos Explorer.

ROVs were first used by the military in the 1960s. By the 1980s, they were becoming widely used by the offshore oil and gas industry. Since then, designs have evolved and capabilities increased so that ROVs can operate at greater depths, carry much higher-resolution cameras, more sensitive sonar, and more capable manipulator arms. They can be controlled from the surface using fiber optics communication systems. Depending upon an ROV's size and capabilities, price tags can range from a few thousand to several million dollars.

ROVs come in many shapes and sizes. Heavy-duty models can weigh several tons and have 250-horsepower motors. The largest are used to dig trenches for laying underwater pipelines.

ROVs of 15 kilograms or less can examine the interior of pipelines and other small cavities or carry out tedious operations, such as checking ship hulls for terrorist devices. Larger ROVs are used at depths down to 1,000 meters. They can carry sonar units to sound the sea- floor to identify the best terrain that will support underwater pipelines.

Work-class ROVs usually carry manipulator arms to perform various operations. The frames of light work-class ROVs may be made from polymers instead of stainless steel or aluminum alloys. Heavy work-class ROVs are used in deeper waters, at depths down to 6,500 meters.

The typical work-class ROV is built around an aluminum chassis. It is equipped with electric motors and several propellers for maneuvering, with powerful searchlights to illuminate pitch-black depths, and with as many as eight cameras. Some contain mapping devices. They can be used, for instance, to find where pipelines have shifted after storms. Some pipelines in the Gulf of Mexico were moved several miles by Hurricanes Katrina and Rita.

View from Above: Seen through its onboard camera, an ROV uses its manipulator arm to extract samples from a coral formation.

Large ROVs can carry grasping claws that will lift and maneuver loads of as much as 100 kilograms. Tool options include cutting wheels that can slice through steel and high-pressure water jets. Electrical power, up to 500 volts, is supplied through a tether connecting the ROV to a control room in the surface platform or on a ship. The robots are operated by crews.

"Crew size depends on the operator's preferences, the type of work being performed, and the schedule available to perform the work," according to Jason Stanley, vice president of systems sales and the Gulf of Mexico regional manager for Schilling Robotics. "Crews start at three people, and for installations using two ROV systems at once (which is quite common), the crew can reach 10 to 12 people."

Equipped for the Job

Some of the ROVs used for deep work can be massive - about 5,000 kilograms—and can come equipped with a variety of robot arms, thrusters, cameras, and other equipment.

Schilling Robotics, based in Davis, Calif., makes an ROV of this class that it markets under the trademark UHD (for "ultra heavy duty"). The vehicle is rated for depths of 4,000 meters, or about 2.5 miles. This unit is 3 meters long and 1.9 meters wide. It can be equipped with a variety of accessories adding up to 300 kilograms. To move all of this weight underwater, the UHD is equipped with a 150-hp or 200-hp motor. It is provided with advanced automatic controls for maneuvering and a dynamic positioning device to hold a position.

The digital telemetry system is based on a gigabyte Ethernet backbone and provides serial, video, and Ethernet communications. High-definition video is standard. The vehicle has two standard manipulator arms, a seven-function arm called Titan 4, and a five-function arm called RigMaster. Other robotic arms are available.

ROVs: It Isn't Playtime

Controlling ROVs on the ocean floor often requires their operators to use joysticks. However, it's definitely not like playing a video game. Periods of tension alternate with periods of routine. ROVs often work 24/7 and require operating crews to work in shifts. ROV control rooms are located in drilling or production platforms or in ships.

"Typically, the three-person ROV control room crew includes a pilot, copilot, and supervisor," said Tyler Schilling, chairman and chief development officer of Schilling Robotics.

One challenging task for ROVs is enabling companies to map oil- and gas-bearing rock formations deep below the ocean floor. The seismic surveys use devices that record sonic waves reflected from rock formations. According to Schilling, "These devices look like big hockey pucks 2 feet in diameter and 1 foot thick. In water, each weighs a little over 100 pounds."

Phoenix International, an ROV operator, recently used a Schilling Robotics UHD to enable seismic survey firm Fairfield International to carry out a survey in the Gulf of Mexico in waters more than 1,000 meters deep. More than 900 seismic devices were required for this survey. These operations can cost millions of dollars, so a single misstep can be very expensive.

The UHD used was fitted with a carrier holding 12 seismic devices. "The UHD's horsepower enables it to move at two knots flying over the ocean floor from one position to another," Schilling said. One of the UHD's manipulator arms placed each seismic device in the desired position.

"Each hockey puck must be exactly positioned on the ocean floor to create high-resolution images of the underlying rock formations," Schilling said. "The devices were placed in a matrix 300 meters apart." Operators at the surface used the UHD's GPS and dynamic positioning capabilities to exactly position the ROV before a manipulator arm placed the seismic device on the ocean floor. It also is essential that the manipulator position each device in an exactly horizontal orientation. Images from the UHD's cameras enabled ROV operators to achieve this horizontal positioning. Then, the operators navigate the ROV to the next position.

Deployment of all 900 seismic devices took many days with ROV control room crews working around the clock. Once all seismic devices were in place, a surface vessel aimed sonic bursts at the ocean floor. These shock waves penetrated underlying rock formations and were reflected back to the seismic devices, which took readings. After the vessel fired all the necessary sonic shots, the UHV had to go down and retrieve all the devices. The data had to be downloaded from them and analyzed.

The results of the analysis may result in a drilling rig being brought onsite to drill exploratory wells. That would give ROVs even more work to do.

According to Stanley, "The UHD is typically used for heavy-duty construction tasks. This includes assisting with installation of large subsea hardware items, such as well equipment and pipelines. Depending on the launch equipment, the vehicles can take from one to two hours to deploy and recover from a depth of 4,000 meters."

The ROV systems can work long shifts. "If the systems are well maintained and the operating weather is reasonably good, the vehicles have been able to work nonstop for three to seven days without being recovered," Stanley said.

The manipulator arms of most ROVs are sophisticated enough to install and maintain equipment positioned on the ocean floor and to work on underwater portions of production platforms. The manipulator arms of many ROVs are commonly fitted with "lobster claws" or "parallel closure jaws" for gripping objects and other tools, such as rotary cutting tools.

The Sea Mantis ROV from DOER Marine, for example, has a mandible cutter that can slice through steel cables, hardened steel rods, and Kevlar. The cutter is controlled through a PC using a USB joystick. Such devices are often fitted with 360-degree rotation "wrists" to enable precise positioning. Claws, cutters, and other tools are designed to be readily detachable for maintenance and replacement by other tools.

According to Wes Gerriets, vice president of sales and marketing for manipulators at Schilling Robotics, "A work-class ROV typically carries two manipulator arms—usually a dexterous, high-precision arm paired with a stronger, but less-dexterous grabber arm. Manipulators can also deploy a torque tool, cut ropes and wires, perform grinding operations, clean surfaces with water jets or brushes, and hold a nozzle connected to a suction pump for dredging operations."

Smaller units designed for shallower depths are often constructed around a polypropylene chassis. The plastic resists corrosion and makes the vehicle lighter; the less an ROV weighs, the smaller the surface craft needed to launch and retrieve it. For example, VideoRay LLC, based in Phoenixville, Pa., produces the VideoRay line of ROVs. Used for underwater equipment inspections, the VideoRay submersible weighs just 4 kg and is rated for depths of 76 meters.

Deep Ocean Engineering in San Leandro, Calif., makes a 105 kg vehicle called the Vector M-5 that can operate at depths to 3,300 meters. It is 107 centimeters long, 80 cm wide, and 76 cm high. Forward thrust is up to 670 newtons, or about 150 pounds, and lateral thrust is just over 220 N. Input power is 230 V ac at a frequency of 50 to 60 Hz. The power rating is 10 kVA. Two 250-watt quartz-halogen lamps provide adjustable lighting to enable better photography.

A digital communications link provides control of vehicle functions using three continuous video channels. A continuously updated video display provides the operator with compass heading, depth, thruster turn count, and other information, including optional temperature or GPS position. Navigation is accomplished using a gyro-stabilized, solid-state magnetic compass unit and an electronic depth sensor.

Transocean's Ian Hudson believes the ability of ROVs to give a close-up look at the sea floor can play a role not only in commercial activities, but also in monitoring the health of the undersea environment.

"With being able to take a firsthand view of the seafloor and sampling to the centimeter scale, you have a very powerful tool for predicting environmental effects and also the speed of recovery, a fundamentally difficult measurement to make without ROV technology," he said.

Academic scientists use ROVs for a variety of marine biology studies. Many of them operate their ROVs from research vessels or use oil platform ROV time that is donated by oil companies. For example, Sean Powers, a marine biologist at the University of South Alabama, operates a $50,000 Seabotics ROV equipped with sensors and a manipulator. He uses it to study snapper, grouper, and tuna populations and their behavior around oil platforms.

According to Powers, non-producing platforms "turn into wonderful artificial reefs that attract a lot of fish." This is good since there are few natural reefs in the Gulf of Mexico.

Next Generation

Chris Nicholson of Deep Sea Systems sees further applications for ROVs in the future. For instance, they may one day help to build structures that generate energy from deep-sea currents or from ocean temperature gradients. He suggests that someday they will also mine the ocean floor for minerals.

ROVs capable of operating at greater depths are under development by research institutions and commercial manufacturers. Engineers at Woods Hole Oceanographic Institute in Massachusetts are testing an ROV capable of operating at depths greater than 11,000 meters - deeper than Mount Everest is tall. Its purpose will be to explore the deepest parts of the ocean floor. Its advanced capabilities will teach manufacturers how to design other ROVs to transcend the current depth limits for industrial operations.

DOER Marine is working with Northern Illinois University to develop an ROV capable of being lowered through a borehole drilled though an ice sheet to enter the underlying ocean.

"Design challenges include reducing ROV weight and size while still having adequate strength of the components," said Tony Lawson, DOER Marine's engineering director.

Acording to Nicholson, ROV manufacturers are working toward "super reliability," so that vehicles can be put on the sea floor to operate for six to eight months at a time and be based at subsea facilities.

John K. Borchardt, a freelance writer based in Houston, is a 21-year veteran of the oil and gas industry.