What is a Remotely Operated Underwater Vehicle (ROV)?
A Remotely Operated Underwater Vehicle, also known as an ROV, is an unmanned robot typically tethered by an operator. It is an underwater robot used to collect data about the underwater world, including ocean structures or geological formations such as hydrothermal vents. The robot utilizes remote control and autonomous control technology, making it safe and easy to operate.
Observational ROVs are used to explore the ocean, providing high-resolution images and video for research and study. Unmanned robots are equipped with additional equipment, such as water sampling devices and joysticks. Modern ROVs have a battery life of up to eight hours.
Fiber optic cables connect the operator to the ROV, enabling its mobility.
Remotely Operated Underwater Vehicles (ROVs) are highly sophisticated and have a wide range of uses, from exploration and unmanned missions to research and sporting events. They are used by scientists, zoologists, botanists, and others. Many industries, such as aquaculture and agriculture, utilize these devices for routine infrastructure inspections and repairs.
In this article, we will discuss some of the notable features, uses, classifications, preparation, launching, operation, and shortcomings of remotely operated vehicles (ROVs).
What is a remotely operated vehicle (ROV)?
An ROV is essentially a robot that can operate underwater. Its functionality is similar to that of a miniature submarine, but without a human operator.
They can be operated wirelessly or via wired connections, with the latter being more common. These highly complex ROVs are composed of multiple subsystems.
The various components that make up the overall operating mechanism of an ROV include:
1. Electrical system (wiring and circuitry);
2. Mechanical structure;
3. Sensors and accessories;
4. Mission-specific structures.
The fundamental structure supporting all of these systems is the ROV’s frame. The frame is designed to be as lightweight as possible to avoid excessive weight and drag during movement.
The frame uses a multi-layered construction to prevent accidental damage to internal components. Frame elements are equipped with clips to support wiring and other circuit components.
The frame is designed to withstand severe impact and utilizes the principles of triangulation from solid mechanics. To understand how triangulation works, consider a square frame.
Any force acting on the frame’s vertices would cause it to bend and collapse. Therefore, diagonal elements are used to provide additional tensile strength.
Adding just one element increases the forces acting on the frame. X-shaped connections are also added to vulnerable areas, along with two diagonal elements, to increase tensile and compressive strength.
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Subsystems and Materials Used in Remotely Operated Vehicle (ROV) Design
The electrical system refers to the wiring and circuitry that form the core of a remotely operated vehicle (ROV). Their effectiveness and suitability for a wide range of applications stem from the highly robust and complex electronics. Key components include the motherboard and processing unit, which receive inputs from a control unit and convert them into physical outputs.
In most cases, control units are manually operated, making autonomous underwater vehicles (AUVs) less common in this field due to the challenges involved.
Depending on the level of innovation and design, the inputs to the control unit can be wired or wireless. They can also be task-specific. For example, a wired robot might become entangled at an underwater shipwreck site.
Conversely, as the robot progresses deeper into the wreck, wireless signals may be blocked. Therefore, operating conditions and potential hazards must be carefully assessed.
After the signal reaches the onboard receiver, it is transmitted to the mechanical system. The primary system is the propulsion system, which utilizes specialized miniature marine propellers.
These robots are driven by small servo motors housed in a waterproof housing, each shaft equipped with a propeller with three to five blades. The propellers can rotate clockwise or counterclockwise to provide steering.
Some advanced remotely operated vehicles (ROVs) used for shipwreck analysis and deep-sea exploration are equipped with articulated rotor propellers. These propellers are rarely used and more expensive than fixed propellers. They are only required when extreme precision is required.
Sensors and accessories form the core of an ROV’s functionality. The most common equipment includes cameras, depth gauges, temperature gauges, and internal system sensors.
Operators use cameras because they must monitor their surroundings. Depth gauges ensure the ROV is at the desired depth and does not sink into high-pressure areas.
Temperature zones detect changes in water temperature and aid in the observation of thermal vents and thermoclines on the seafloor. Finally, internal system sensors ensure the ROV operates efficiently.
Temperature zoning monitors water temperature fluctuations and helps visualize thermal vents and thermal layers on the seafloor. Finally, the system’s internal sensors ensure the ROV operates efficiently and that all systems are functioning as expected.
Mission-specific modifications make ROVs customizable and usable for a variety of applications. For example, in historical exploration and shipwreck exploration, robotic arms and tools can be used to collect artifacts.
For seafloor geological surveys, ROVs can be equipped with rock-cutting tools to extract samples for analysis. For seafloor mapping, ROVs can be equipped with lidar, sonar, or radar to receive waves reflected from sea ridges and valleys.
While typically equipped with a main camera, specialized cameras capable of capturing thermal images, high-resolution imaging, microlenses, and more are also available.
Material selection is crucial for ROVs. The structure must be lightweight enough to avoid compromising the robot’s performance, yet robust enough to withstand minor to severe impacts.
Electrical systems must be encased in insulation and housed in waterproof containers. Special attention must be paid to corrosion-resistant materials to avoid any problems during operation.
Because ROVs spend extended periods underwater, they are less likely to rust (due to a lack of oxygen, which is essential for rust).
However, when they are on the surface, the potential for corrosion increases (as moisture mixes with atmospheric oxygen). Therefore, ROVs must be thoroughly dried and stored in a dry, clean environment to prevent any fungal growth or corrosion.
Fungal growth in seawater can be prevented by applying special coatings that break down existing microorganisms and prevent new ones from attaching to the ROV’s surface underwater.
Using ROVs
ROVs are versatile and come with a variety of equipment. Therefore, most ROV manufacturers offer a basic, customizable structure or chassis. This basic chassis is called the ROV’s “frame” or “mold.” This section discusses the various uses of this equipment.
Underwater ROVs utilize modern technology. They are equipped with lighting systems and cameras to better capture underwater panoramas, aiding in geological education and marine life identification.
Underwater Remotely Operated Vehicles
With the continuous advancement of technology, the latest technical concepts are being applied to ROVs, significantly enhancing their capabilities. Additional equipment includes fixed cameras, water sampling devices, and even processing units.
ROVs can also be equipped with advanced equipment to accurately measure and assess current temperature, light transmittance, and water clarity.
These devices are often used on scientific and exploratory ROVs to understand the underwater environment. Chemical analysis equipment can also study the qualitative composition of water at different locations and depths.
Robotic underwater vehicles (ROVs) were invented primarily for industrial purposes, such as regular inspections of pipelines (internal and external) and structural testing on specialized platforms in various offshore locations.
These robots are also used to explore marine shipwrecks and historical sites and meet the needs of many scientific expeditions and aquarium educational programs.
Robotic Underwater Vehicle (ROV) Classification
Robotic underwater vehicles (ROVs) can be divided into different categories based on their weight, power, functionality, and size. Micro ROVs are compact and weigh less than 3 kilograms.
The main categories are as follows:
1. Micro ROV
2. Mini ROV
3. General-Purpose ROV
4. Inspection ROV
5. Lightweight ROV
6. Heavyweight ROV
7. Trenching and Burial ROV
These features enable ROVs to explore tiny cavities or cracks in pipelines, tasks that would be nearly impossible for divers to perform.
Micro ROVs are compact and weigh less than 3 kg. These features enable them to explore tiny cavities or cracks in pipelines, tasks that would be nearly impossible for divers to perform.
On the other hand, micro ROVs typically weigh around 15 kg. They can be efficiently operated by a single person from a boat for underwater exploration.
The micro and small ROV categories are somewhat of a “special interest” category, as they do not participate in intervention operations.
General-purpose ROVs typically have less than 5 horsepower of propulsion and utilize three-finger steering, like the older RCV 225. These ROVs are designed to assist with light survey missions and typically carry sonar equipment.
The standard underwater depth is approximately 1,000 meters, but one remotely operated vehicle (ROV) has been upgraded to 7,000 meters.
Lightwork Remotely Operated Vehicles (ROVs) typically have power below 50 horsepower and support multiple operating modes. These vehicles have a maximum operating depth of 2,000 meters. They utilize a polymer polyethylene construction, unlike traditional aluminum alloys or stainless steel.
Heavyweight ROVs have power below 220 horsepower, can operate in two modes, and can operate at depths of up to 3,500 meters.
These ROVs can carry lift loads exceeding 5,000 kg and can be modified to support multiple operating modes. The most common applications for these heavyweight ROVs are deepwater installation and subsea connections.
Trenching ROVs have power ranging from 200 to 500 horsepower and can operate at depths of up to 6,000 meters. While most ROVs have propulsion systems below 500 horsepower, some have power approaching or exceeding 600 horsepower.
These ROVs are often used to lay cables, safely construct subsea trenches, and partially or fully bury subsea components used in the oil and gas industry.
Finally, ROVs can be further categorized based on how they are launched. A system called a tether management system (TMS) controls the distribution of the umbilical cable that powers and controls the ROV. When these ROVs are directly tethered to a ship or observation platform, they are referred to as free-floating ROVs.
In this case, they are neutrally buoyant. On the other hand, some ROVs are stored in a compartment called a “garage” and then lowered into the sea.
During launch, the ROV is released from its underwater compartment, its tether attached to the robotic garage rather than to the vessel. The choice of launch system depends on the application, depth, functionality, and geographic factors.
Preparing and Launching an ROV
ROVs come in a wide range of sizes, from small breadboxes to small trucks. Preparing and launching an ROV is straightforward, as the robot can be easily lowered into the water from a ship.
The recovery process may require a large crane to lift the robot out of the water. Typically, an A-frame is used to safely lower the ROV back to the surface.
Sometimes, various structures called “robot hangars” are used, which can be lowered to the stern. These hangars serve as temporary safe havens from which the ROV can return to the area after the expedition.
Occasional ROV expeditions are much safer than conventional diving, which can result in personal injury or even death.
Deploying Remotely Operated Vehicles (ROVs) at Sea
ROVs have proven very effective in handling submarines, as their cutting blades or motorized booms can aid in the recovery of submarines that become stuck and unable to move freely.
One of the drawbacks of submarine projects is that bad weather can pose a significant obstacle, while ROVs are not. Furthermore, researchers can first submerge the ROV to explore the details of a specific underwater location and then determine whether it is safe enough for submarine deployment.
Before removing the ROV from the side of the ship or launching it from a platform, it needs to be gently lowered into the water. Due to the risk of damaging sensitive equipment on board, water jets are prohibited. The ROV can be lowered using a crane or, if buoyancy is insufficient, manually.
A moonbath can be used in rough waters, increasing the risk of damage when entering the spray zone. A moonbath is a device enclosed in a hollow container with the water surface at its lower end.
A column of water forms within the pool, creating a relatively still flow. Shock absorbers are also used to reduce heave and fall motions, preventing damage from resonance. Remotely operated vehicles (ROVs) can be lowered through the moonbath in adverse weather conditions.
Famous ROVs
Among the most notable underwater ROVs is the hydraulically driven Ventana, which can dive to a depth of 1,850 meters. Ventana is operated from the deck of the Royal Navy’s Point Lobos.
MBARI, on the other hand, acquired the Doc Ricketts ROV in 2008, which has an impressive diving depth of 4,000 meters.
Since then, this ROV has been continuously modernized. The Doc Ricketts was an ideal replacement for the previous Tiburon, which was also capable of diving to depths of 2.5 miles.
These unique submersibles made it easier to explore many deep-sea oil and gas reserves. Many oil reserves were previously difficult for divers to locate, which caused significant setbacks to commercial operations.
Interestingly, the wrecks of several famous ships, such as the RMS Titanic, the USS Yorktown, the USS Central America, and the German battleship Bismarck, were discovered with the assistance of the RMS Submarine Division.
In the case of Central America, a remotely operated underwater vehicle (ROV) was able to track and collect critical materials from the seafloor.
Disadvantages
The preferred design uses a high-power signal to allow remote control of the ROV. This would provide a wider signal range than current fixed structures. However, this high power and frequency could potentially affect marine life.
Another option is to use a low-power main signal, periodically coupled with multiple amplifiers to extend the ROV’s signal range.
While this option is more expensive, it is environmentally preferable. Unfortunately, the low-power option can lead to surface saturation due to the increased number of amplifiers required.
A major disadvantage of ROVs is the lack of a human operator, which makes underwater visual surveys difficult. The ROV is tethered to the host vessel on the surface via complex cables, limiting its freedom of movement.
Currently, research and innovation are underway in the field of wireless control of ROVs. The proposed design proposes two main implementation models.
The preferred design uses a high-power signal to allow remote control of the ROV. This design provides wider coverage than existing tethered designs. However, the high power and high frequency may affect marine life.
Another option is to connect a low-power main signal to multiple amplifiers and reconnect them periodically to extend the range of the remotely operated vehicle (ROV). While more expensive, this is a better option from an environmental perspective.
Unfortunately, the low-power approach has the potential to saturate the sea surface due to the need for more amplifiers.
Frequently Asked Questions
1. What is a Remotely Operated Vehicle (ROV)?
A remotely operated underwater vehicle (ROV), also known as an ROV, is an unmanned submersible that is typically tethered by an operator. It is an underwater robot used to collect data about the underwater world, including underwater geological structures or formations, such as hydrothermal vents.
2. What is an ROV used for?
ROVs are used to observe the ocean, providing high-resolution imagery and high-definition video for research and study. ROVs are sophisticated and perform a variety of functions, from exploration and unmanned expeditions to research and sporting events. Scientists, zoologists, botanists, and others use them. Many industries, such as aquaculture and agriculture, use them for routine inspections and repairs of infrastructure.
3. How do they operate?
These submersibles use remote controls and automated control technology, making them safe and convenient to operate. Unmanned submersibles are equipped with additional equipment such as water sampling devices and joysticks. Modern remotely operated vehicles (ROVs) have a battery life of 8 hours.
4. What are the most popular remotely operated vehicles (ROVs)?
The Ventana is hydraulically driven and can dive to a maximum depth of 1,850 meters. It is operated from the deck of the Royal Navy’s HMS Point Lobos. MBARI acquired the Doc Ricketts ROV in 2008, which has excellent performance and can dive to a depth of 4,000 meters.
5. What have ROVs achieved?
They have facilitated the exploration of various oil and gas reserves in the deep sea, many of which were previously difficult for divers to find. Additionally, thanks to the development of the ROV industry, the wrecks of famous ships such as the RMS Titanic, the USS Yorktown, the USS Central America, and the German battleship Bismarck have been discovered.
