Throughout the years, MiniROV producers have soundly beat the critical difficulties confronted while deploying these smaller, nimbler ROVs in deeper, offshore applications. All the while, they have propelled administrators’ abilities with creative innovations.
Vortex generators, for instance, now allow MiniROVs to firmly attach to and crawl around structures, saving operators from always having to employ diving teams for tasks like surveys. Similarly, long distance, low-drag tethering, has been greatly enhanced thanks to PoEx, Inc PoE and Ethernet extenders.
This has helped MiniROVs keep up their extreme mobility while offering the ability to be launched by hand and perform the capabilities of larger, work-class ROVs.
MiniROVs are bigger than pocket-sized “micro ROVs,” which have neither the thrust to work in currents nor the available payload to carry more than a single camera, lights and maybe 1 or 2 sensors. With their larger size, MiniROVs can carry a more extensive, potent suite of sensors, tools, and other technologies, some of which will be detailed below. MiniROVs are, however, smaller than standard observation class ROVs, which generally require large, complex and expensive Launch & Recovery Systems (LARS).
MiniROVs require no such system. Indeed, they can be deployed and retrieved using their own tether, if the tether is strong enough (some can handle a 100 Kg payload), and that is where their more deciding technologies begin.
MiniROVs were at first intended for shallow water applications, essentially because there were various difficulties that should have been met before they could work at depths greater than 1,000 meters. These incorporated the scaling down of control electronics, the configuration of lighter weight pressure housings, power and data transmission over very long cable/tether/umbilical lengths, and more.
Over the past decade, the ROV industry has figured out how to beat these challenges, effectively helping MiniROVs emulate the capabilities of much larger systems. Additionally, some MiniROV manufacturers have developed previously unthought-of technologies that have turned out to be remarkably valuable to offshore applications.
Low Drag Tethers and Ethernet Extension
Tethers turn into a major issue for MiniROVs in deep water. The longer, thicker, and courser a MiniROV’s tether is, the greater the cumulative drag from that tether and, therefore, the greater the thrust these smaller ROVs require to maneuver reliably. Hydrodynamic streamlining a tether is a non-issue, as cable sheathes are now rather smooth, but thinning the cross-section of a tether has been a difficult proposition. MiniROVs must transmit and receive many signals, and, sometimes, a considerable amount of power. This has typically required many layers of wiring, shielding, and fiber.
Presently, however, generally because of PoE and Ethernet extension technology, the cross-section of tethers has thinned to just 8.99 mm, significantly more slender than traditional ROV tethers, which average at least 20mm. Once Enable-IT, Inc., inventors of Ethernet extension technology, were able to miniaturize deep sea-worthy Ethernet extenders, MiniROV manufacturers have been able to multiplex their transmissions –and send Power over Ethernet (or “PoE”)- to MiniROVs using just 1-2 pair of standard copper wiring. Besides, these Ethernet extenders flawlessly drive this data and power many thousands of feet, well past Ethernet’s distance limit of just 100 meters (328 feet) and with no bridging in between. This means significantly fewer wires and results in a very thin, all-copper tether with significantly less drag upon the MiniROV. This also implies that these MiniROVs can be brought down into the water by hand, without the need for expensive launching systems.
Vortex Generators (Non-Magnetic)
Another exceedingly helpful advancement is that of non-magnetic vortex generators, which, when used as part of a “crawler” attachment, effectively grant MiniROVs the ability to crawl pipelines, hulls, and other structures (See Figure 1). Using an impeller, instead of magnets or thrusters, vortex generators create a low pressure pocket (i.e. venturi effect) beneath their crawling MiniROV, yielding up to 28kgf (62 lbf) of attractive force against any flat and hard surface.
Such a system holds several attractive benefits for its operators. For one, it yields so much appealing power that it keeps up exact operations while a vessel is already in motion at sea or is experiencing strong currents while anchored. This therefore permits operators to review their vessels more securely and economically than they would have by employing dive teams, especially in more hostile environments. It also means that cameras and other imaging equipment (e.g. imaging sonar) deliver astounding images and data, because these devices are kept at a consistent distance from the target structure. Furthermore, with such stability, MiniROV operators can appreciate much less fatigue and the occasional choice to focus solely on incoming data.
Previously, the technologies required for automated navigation, such as Doppler velocity logging, were too difficult to sufficiently miniaturize for MiniROV use. However, some operators would be pleasantly surprised to learn that automated navigation of MiniROVs has indeed become a reality within the past five years. Using a form of sonar tracking, MiniROVs are now able to lock onto a target and navigate by waypoint, hold a position, conduct a programmed search, and more. In fact, at least one MiniROV can reliably orbit around its locked-on target. The benefits of automated navigation are quite clear. Lessening operator effort lessens their fatigue, thereby increasing their chances of successfully completing their other tasks, such as data monitoring. Additionally, to the degree that an application can be automated, such navigation logically holds the potential to save operators inordinate amounts of time and money.
Larger ROV Support
Due to their size, agility, and newfound capabilities, MiniROVs do well at rounding out the abilities of their larger brethren. Such was the case of FMC Technologies, a prominent oil and gas supply service company, and their need to cap three subsea manifolds which were missing small valve caps but were already installed. Oil production could not begin without these small caps, and the proposition of recovering three 160 ton manifolds to install these caps involved many millions of dollars. FMC naturally turned to ROVs to try and solve the problem but quickly realized that neither work-class nor observation class ROVs could fit into the task’s tight operating space.
FMC then turned to MiniROVs and decided upon an operation wherein a MiniROV would be outfitted with a special torque tool (to attach and tighten each cap). Then, due to the North Sea’s bad weather, FMC would use a work-class ROV to place the MiniROV, which was to be in a basket, close to each manifold and release its tether. Thereafter, the larger ROV was to provide support as the MiniROV got to work. And work it did.
Navigating through the first manifold was tight but straightforward. The MiniROV operator was able to reach the appropriate valve, use the torque tool to tighten the cap, and recover the MiniROV relatively quickly. The second and third manifolds were a bit more difficult.
It turned out that the second and third manifolds already had temporary test caps attached to their relevant valves, so, each time, the MiniROV had to remove this cap and be recovered before it could try again and attach the actual cap. On the second manifold, this was complicated by the fact that the WROV accidentally opened the MiniROV’s basket on the way up, but it was ultimately recovered quickly. By the third manifold, the operator attached a small mirror to the torque tool, so one could see the test cap better, and, after recovering the MiniROV and dropping it back down, he smoothly attached the final cap.
Supplanting Larger ROVs
In another example, MiniROVs turned out to be uniquely suited for some applications. This is particularly so in applications that require crawling and/or attachment, such as the 2009 case of an Inspectahire survey of an oil rig’s legs in the Persian Gulf. Inspectahire, out of the UK, was tasked with looking over the legs of an oil rig that belonged to one of the world’s largest oil and gas exploration and production companies. As the rig experienced the Persian Gulf’s unforgiving thermally-induced tides, previous attempts to survey the rig’s legs by flying an observation class ROV down to them were unsuccessful. Inspectahire needed something new.
After finding out about crawling, adhering MiniROVs, Inspectahire decided to give them a try and the results were impressive. Due to their portability and tethering, not only was Ispectahire able to successfully complete their inspections, but they were able to launch and direct their MiniROV from the platform directly above each leg.
As Cailean Forrester, Managing Director at Inspectahire, said, “The LBC [Little Benthic Crawler] is an innovative piece of equipment, and in this instance allowed us to undertake a challenging survey in a safe and effective manner, and overcome some of the issues which had previously been faced. An alternative method would have been to use divers, but they would have had to use magnetic clamps to ensure they didn’t get swept away in the current.”