An Autonomous Underwater Vehicle (AUV) operates independently from the ship and has no connecting cables while ROVs are connected to an operator on the surface host ship by a load-carrying umbilical cable which provides communication and control.
A Remotely Operated underwater Vehicle (ROV) is a tethered underwater mobile device. ROVs are unoccupied, highly maneuverable, and operated by a crew either aboard a vessel/floating platform or on proximate land. They are linked to a host ship by a neutrally buoyant tether, a load-carrying umbilical cable which provides communication and control.
Submersible ROVs are normally classified into categories based on their size, weight, ability or power.
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 underwater inspection and survey operations.
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:
- 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)
- The Trident as fully assembled ROV (starting at around USD $1500)
Evolution of the OpenROV
The idea to build OpenROV was pioneered by Eric Stackpole, an engineer at NASA at the time, to discover whether the legend about the hidden treasure of the Hall City Cave was true.
According to the legend, a few renegade Native Americans stole ~100 pounds of gold nuggets from miners in the 1800s, but were chased. To escape from the pursuit, the renegades had to bury the nuggets in deep waters of the nearby Hall City Cave to lighten their load, but could not retrieve the gold, because they were soon caught and hanged. Even though many have tried to find the gold, nobody has been able to get to the bottom of the narrow and deep well of the cave.
“Necessity is the mother of invention”
David Lang, a self-taught sailor from Minnesota, heard about Stackpole building a small, cheap, and robust submarine in his garage to search for the gold and became inspired to join. Matteo Borri designed and built the electronics, software and motor system for a prototype presented at the World Maker Faire in 2011. Lang and Stackpole co-founded OpenROV as an open-source hardware project as a start-up company, and a DIY community.
OpenROV
The OpenROV (figure 1) with a weight of 2.6 kilograms is an example of a Micro Class ROV which is an affordable ROV available assembled or in kit form
The submarine is controlled from a laptop computer connected to the submarine via a tether and is equipped with on-board Light Emitting Diodes (LEDs) and a camera. OpenROV is an open-source hardware project. By providing the list of the submarine parts and instructions on how to assemble them, the developers aim to democratize underwater exploration.
OpenROV connects to your computer via the tether and uses an Ethernet protocol. You can access the ROV cockpit via web browser software (Google Chrome). Flight controls are also simple. You can use either your computer’s keyboard or a gamepad controller to pilot the vehicle during a dive. You can document all your dives by recording the video stream.
OpenROV specifications (for full details see reference 3)
- Maximum depth of 100m (328ft)
- Maximum forward speed of 2 knots
- Live HD video is streamed to the surface control unit over an ultra-thin two-wire tether
- Internal LED Lighting with a brightness of 200 Lumens
- External LED Lighting with a maximum brightness of 1400 lumens
- Water Temperature operational capability is between -10C to 50C
- Software controlled camera tilt (+/- 60 deg from center)
- Tether neutrally buoyant in fresh water
Instrumentation
- Camera supporting HD live video stream in-browser recording of video
- IMU / Depth Sensor for navigation telemetry such as depth, heading, pitch and roll
- Microprocessors for a flexible and powerful developer platform with dozens of input/output channels and plenty of computing power for user-designed features and experiments
- Scaling lasers for size reference during a dive (parallel, 10 cm separation)
- Current and voltage protection with feedback to ensure proper system function
- Communications channel and power for external instrumentation
- Payload area for mounting additional hardware or equipment (170g max payload without adding floatation).
The Trident Micro ROV (for full details see reference 3)
The Trident ROV (figures 2 & 3) also referred to as an underwater drone is a fully assembled product from OpenROV.
Trident ROV specifications
- Maximum depth of 100m (328ft)
- Maximum forward speed of 3.89 knots
- Live HD video 1080p @ 30 fps, using h.264 compression
- 3 forward facing LEDs on each side with total of 360 lumens
- Water Temperature operational capability is between -10C to 50C
- Interface & communications WiFi 802.11 b/g/n, user interaction using a modern Android (minimum 5.1) device through the OpenROV Application
- Tether neutrally buoyant in fresh water
- 3-axis magnetometer, 3-axis gyro, 3-axis accelerometer, centimetre-resolution depth sensor
Affordable Micro-Class ROV technology is within the reach of all marine surveyors and can be utilised in many aspects of marine surveying to further enable the capability of the Marine Surveyor.
References & Resources
- Inspection-Class Remotely Operated Vehicles—A Review: Romano Capocci, Gerard Dooly, Edin Omerdi´c, Joseph Coleman, Thomas Newe and Daniel Toal, Journal of Marine Science & Engineering published: 16 March 2017
- Wikipedia
- OpenROV website
