The many models of remotely operated vehicles in the market cover a spectrum of sizes from very large work class ROVs to hand carryable inspection class ROVs. The definition of an ROV is:
Remotely Operated Vehicle (ROV):
A submersible vehicle consisting of a series of sensors and thrusters providing situational awareness and control for the vehicle to an operator not within the vehicle.
ROVs are involved in every industry that uses or touches water from the shipping industry to pulp and paper and even municipal water supplies. These vehicles are used to both inspect equipment that is in place as well as perform subsea installation and maintenance.
Because of this distinction ROVs are generally divided into two classes defined as:
Inspection class ROV:
An ROV designed primarily for inspections underwater and almost exclusively observation of its environment. Typically small in size to access hard to reach locations and with less powerful thrusters. For more info about these ROVs read these Tips for ROV inspections.
Work Class ROV:
An ROV design primarily for work tasks and interaction with its environment. These vehicles can be very large, have high power thrusters and powerful multi-function robotic arms.
While these are rather loose definitions, it is often up to the equipment manufacturer to market their ROVs with qualifiers to these classes from micro inspection class vehicles to ultra heavy duty work class vehicles as a means of differentiating themselves from the competition and providing prospective users with an understanding of the design intent for the system.
There are a number of vehicles that lie somewhere in the middle of these two classes and in some applications should be considered only for inspection work while in others could be used for the construction and maintenance tasks required. Ultimately the ROV class naming system allows manufacturers to provide customers with an initial understanding of the size and intent of the vehicle. However, it is up to the purchaser to match the performance specifications of the system with their specific usage applications considering vehicle sensors, manipulators, size and power. It is only with this deeper understanding of the performance of the vehicles beyond just their class that the ideal ROV for an application can be determined.