Underwater remotely operated vehicles (ROV) are a subset of Unmanned Underwater Vehicles (UUV) that are directly controlled in real-time by a human operator rather than featuring autonomous operation. Underwater ROVs are designed to overcome the limitations of human divers via a number of factors, such as time spent underwater and maximum depth, and are also safer than employing manned submersibles.
Operated from a support vessel or the shore, marine drones are usually connected to their base of operations via an umbilical tether that provides power, communications and data transfer. Tetherless ROVs are rare due to the fact that radio waves do not travel well through water. However, solutions based on laser/free space optics (FSO) and underwater acoustic technologies are currently under development.
Launch and Recovery
Small portable ROVs can be deployed and recovered by hand. Larger ROV drones may require a LARS (launch and recovery system), which consists of a crane and winch mechanism, and may also utilise a cradle to hold the vehicle as it is raised from or lowered into the water.
Underwater ROVs can also be launched from a moonpool, which is a chamber or opening in a vessel that provides access to the water. This method allows marine drones to be launched in rougher sea conditions, as operators do not have to deal with the effects of increased roll and pitch on a crane arm. Moonpools also allow underwater drones to be launched remotely from unmanned surface vessels (USVs). The USV acts as a data and communications relay between the base of operations and the ROV.
Deep-sea ROVs may require a Tether Management System (TMS), which regulates the length of the tether to minimize the effects of drag forces on the cable and decouples the movement of the support vessel from the underwater drone.
Underwater ROV Classes
The most common classification scheme used by ROV manufacturers for underwater remotely operated vehicles is based on size.
Work-class are the largest and most powerful underwater ROV, able to operate high-power equipment such as heavy-duty manipulators and cable-layers. They utilise a hydraulic pump to allow them to manoeuvre at greater depths, which can be tens of thousands of feet underwater.
Observation- or inspection-class are smaller than work-class and are typically deployed in rivers, lakes, and near-shore environments. They may be fitted with cameras and other sensors, as well as basic manipulators and other tools.
Mini- or micro are portable underwater drones that can typically be carried by one person, and are usually used for pure underwater inspection or sensing tasks due to their limited payload capabilities.
Propulsion and Payloads
ROV underwater vehicles manoeuvre using thrusters, which are electrically or hydraulically powered propellers. ROV companies will usually incorporate multiple thrusters to allow the vehicle to move in multiple directions. Electric thrusters are usually used on smaller battery-powered ROVs, whereas hydraulic thrusters are used on the larger work-classes due to the size and weight of hydraulic equipment.
Basic payloads typically include still and video cameras, as well as lights that enable visibility at depth. They can also be equipped with a wide variety of other payloads, including environmental sampling equipment, manipulators and robotic arms, and sonar.
ROV drones are used for a wide variety of applications within marine construction, industry, research and defense. These may include underwater pipeline and oil rig construction and maintenance, environmental sampling and observation, explosive ordnance disposal (EOD), mine countermeasures (MCM) and more.