Remotely operated vehicle
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Remotely operated underwater vehicles (ROVs) is the common accepted name for tethered underwater robots in the offshore industry. ROVs are unoccupied, highly maneuverable and operated by a person aboard a surface vessel. They are linked to the ship by a tether (sometimes referred to as an umbilical cable), a group of cables that carry electrical signals back and forth between the operator and the vehicle. High power applications will often use hydraulics in addition to electrical cabling. Most ROVs are equipped with at least a video camera and lights. Additional equipment is commonly added to expand the vehicle’s capabilities. These may include sonars, magnetometers, a still camera, a manipulator or cutting arm, water samplers, and instruments that measure water clarity, light penetration and temperature.
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[edit] History
The US Navy funded most of the early ROV technology development in the 1960s. This created the capability to perform deep-sea rescue operations and recover objects from the ocean floor. Building on this technology base; the offshore oil & gas industry created the work class ROVs to assist in the development of offshore oil fields. More than a decade after they were first introduced, ROVs became essential in the 1980s when much of the new offshore development exceeded the reach of human divers. During the mid 1980s the marine ROV industry suffered from serious stagnation in technological development caused in part by a drop in the price of oil and a global economic recession. Since then, technological development in the ROV industry has accelerated and today ROVs perform numerous tasks in many fields. Their tasks range from simple inspection of subsea structures, pipeline and platforms to connecting pipelines and placing underwater manifolds. They are used extensively both in the initial construction of a sub-sea development and the subsequent repair and maintenance.
Submersible ROVs have been used to locate many historic shipwrecks, including that of the RMS Titanic, the Bismarck, USS Yorktown, and SS Central America. In some cases, such as the SS Central America, ROVs have been used to recover material from the sea floor and bring it to the surface.
However, there is a lot of work that remains to be done. More than half of the earth’s ocean is deeper than 3000 meters, which is the current working depth of most of the ROV technology. As of the writing of this article, the deeper half of the ocean has never been explored. This vast area has the potential to meet much of humanity’s needs for raw materials. As the industry advances to meet these challenges, we will undoubtedly see further improvements in these complicated robots.
While the oil & gas industry uses the majority of ROVs; other applications include science, military and salvage. Science usage is discussed below, the military uses ROV for tasks such as mine clearing and inspection. Approximately a dozen times per year ROVs are used in marine salvage operations of downed planes and sunken ships.
[edit] Construction
Conventional ROVs are constructed with a large flotation pack on top of a steel or alloy chassis, to provide the necessary buoyancy. Syntactic foam is often used for the flotation. A tool sled may be fitted at the bottom of the system and can accommodate a variety of sensors. By placing the light components on the top and the heavy components on the bottom, the overall system has a large separation between the center of buoyancy and the center of gravity, this provides stability and the stiffness to do work underwater.
Electrical cables may be run inside oil-filled tubing to protect them from corrosion in seawater. Thrusters are usually located in all three axes to provide full control. Cameras, lights and manipulators are on the front of the ROV or occasionally in the rear for assistance in maneuvering.
The majority of the work class ROVs are constructed as described above, however this is not the only style in ROV building. Specifically the smaller ROVs can have very different designs each geared towards their own task. One company's ROV even has wings that allow the vehicle to move more efficiently, while being towed or working in high currents.
[edit] Science ROVs
ROVs are also used extensively by the science community to study the ocean. A number of deep sea animals and plants have been discovered or studied in their natural environment through the use of ROVs: examples include the jellyfish Bumpy and the eel-like halosaurs. In the USA, cutting edge work is done at several public and private oceanographic institutions, including the Monterey Bay Aquarium Research Institute (MBARI), the Woods Hole Oceanographic Institution (WHOI), and the University of Rhode Island / Institute for Exploration (URI/IFE). The picture to the right shows a the behavior and microdistribution of krill under the ice of Antarctica.
Science ROV's take many shapes and sizes. Since good video footage is a core component of most deep-sea scientific research, research ROV's tend to be outfitted with high-output lighting systems and broadcast quality cameras. Depending on the research being conducted, a science ROV will be equipped with various sampling devices and sensors. Many of these devices are one-of-a-kind, state-of-the-art experimental components that have been configured to work in the extreme environment of the deep ocean. Science ROV's also incorporate a good deal of technology that has been developed for the commercial ROV sector, such as hydraulic manipulators and highly accurate subsea navigation systems.
While there are many interesting and unique science ROV's, there are a few larger high-end systems that are worth taking a look at. MBARI's Tiburon vehicle cost over $6 million US dollars to develop and is used primarily for midwater and hydrothermal research on the West Coast of the US. WHOI's Jason system has made many significant contributions to deep-sea oceanographic research and continues to work all over the globe. URI/IFE's Hercules ROV is one of the first science ROV's to fully incorporate a hydraulic propulsion system and is uniquely outfitted to survey and excavate ancient and modern shipwrecks.
[edit] Classification
Submersible ROVs are normally classified into categories based on their size, weight, ability or power. Some common ratings are:
- Micro - typically Micro class ROVs are very small in size and weight. Today’s Micro Class ROVs can weigh less than 3 kg. These ROVs are used as an alternative to a diver, specifically in places where a diver might not be able to go.
- Mini - typically Mini Class ROVs weigh in around 15 kg. Mini Class ROVs are also used as a diver alternative. One person is able to transport the complete ROV system out with them on a small boat, deploy it and complete the job without outside help.
- General - typically less than 5 HP (propulsion); occasionally small three finger manipulators grippers have been installed, such as on the very early RCV 225. These ROVs are able to carry a sonar unit and are usually used on light survey applications. Typically the maximum working depth is less than 1,000 metres though one has been developed to go as deep as 7,000 m.
- Light Workclass - typically less than 50 hp (propulsion). These ROVs may be able to carry some manipulators. Their chassis are often made from polymers such as polyethylene. They typically have a maximum working depth less than 2000 m.
- Heavy Workclass - typically less than 220 hp (propulsion) with an ability to carry at least two manipulators. They have a working depth up to 3500 m.
- Trenching/Burial - typically more than 200 hp (propulsion) and not usually greater than 500 hp (while some do exceed that) with an ability to carry a cable laying sled and work at depths up to 6000 m in some cases.
Submersible ROVs may be "free swimming" where they operate neutrally buoyant on a tether from the launch ship or platform, or they may be "garaged" where they operate from a submersible "garage" or "tophat" on a tether attached to the heavy garage that is lowered from the ship or platform. Both techniques have their pros and cons; however very deep work is normally done with a garage.
