More detailed common ratings are:


• Micro - typically Micro-class ROVs are very small in size and weight. Today’s Micro-Class ROVs typically weigh less than 3 kg. These ROVs are used as an alternative to a diver. They can also be referred to as “underwater drones”


• Mini - typically Mini-Class ROVs weigh in around 15 kg. Mini-Class ROVs are also used as a diver alternative. One person may be able to transport the complete ROV system out with them on a small boat, deploy it and complete the job without outside help. Some Micro and Mini classes are referred to as “eyeball”-class to differentiate them from ROVs that may be able to perform intervention tasks.


• 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 may be 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.


• Inspection Class - these are typically rugged commercial or industrial use observation and data gathering ROVs - typically equipped with live-feed video, still photography, sonar, and other data collection sensors. Inspection Class ROVs can also have manipulator arms for light work and object manipulation.


• Light Work-class - typically less than 50 hp (propulsion). These ROVs may be able to carry some manipulators. Their chassis may be made from polymers such as polyethylene rather than the conventional stainless steel or aluminium alloys. They typically have a maximum working depth less than 2000 m.


• Heavy Work-class - 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.


The shapes and form factors of inspection-class ROV shapes are varied and individual. The most common design for medium sized ROVs is an open frame design, while shapes of ROVs in the micro range, are varied and typically focused on the hydrodynamics of the vehicle.


The Micro Class of ROV can be a valuable tool for the marine surveyor to enable under- water inspection and survey operations.


Background picture courtesy OpenROV Micro Class ROV being used for inspection.


OpenROV has made ROV technology available at prices which put ownership of a Micro Class ROV within the reach of most marine surveyors.


Their offering currently includes two Micro Class ROVs:


1. The OpenROV and open source hardware ROV that can be built from individual parts or purchasing a kit of parts for you to assemble (starting at around USD $900)


2. The Trident as fully assembled ROV (starting at around USD $1500)


The Report • December 2018 • Issue 86 | 67


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