ONT April 2011 : Page 33

ROV Sensors & Subsystems ROVs and one company is offering ROV DP systems that can be retrofitted to any existing Work or Observation Class ROV. Every Work and Observation Class ROV has a single beam imaging sonar to give the pilot a long range (100 – 200 meters) view of what lies ahead. These systems have been available since the early 1980’s and they work very well. Their ability to produce very high resolution images and their relatively low cost have made them indispensable. Their biggest drawback is that to pro-duce those excellent images, the ROV must be stationary. Any movement will cause distortion of the image. Today, Multibeam sonars are being installed on more and more ROV’s. Their ability to give pilots up to 100 meter forward view of the ROV, updated several times a second, makes this a particu-larly useful tool for navigating ROV’s. Very recently multibeams have been introduced that can image objects as close as 8 – 10 inches all the way out to 100 meters. The short range capability can be used to perform manipulator tasks in zero visibility. The small size, lower cost, power requirements and telemetry of these sonars allow for installation on virtually any Work Class or Observation Class ROV. You would be hard pressed to enter a hardware store today to buy a typical flashlight (torch) that does not come with LED (Light Emitting Diode) lights. The same can be said of ROV lighting. LED lighting’s advantages over conventional incan-descent or gas discharge lighting are numerous and include greater ruggedness, brightness, brightness control, color quality, and power efficiency. LED lights are less expensive than HID (High Intensity Discharge) lighting and there are no expensive bulbs to replace. Underwater Positioning, Communications and Control Acoustic positioning systems are available today that utilize spread spectrum signal technology. Advantages over traditional acoustics include increased accuracy, longer range, reduced multi path, and increased telemetry data rates. Because acoustic signals travel long distances in water, it makes them very useful for con-trol of subsea devices, such as backup control of BOPs (Blow Out Preventers), but their data rate is limited (10kbits/sec). For short range underwater communications, RF (Radio Frequency) can transfer data at up to 100kbits/second. ROV-mounted RF units can be deployed to subsea fields that have RF equipped control systems where they can monitor sensors and control functions such as opening or closing valves. Utilizing new non-contact inductive coupling technology, the ROV can even recharge bat-tery packs, all while in close proximity to the subsea device with which it is communicating. Complex vessel-to-vessel communication has emerged in the wake of Macondo where as many as 17 DP vessels were working in very close proximity to each other. A mesh network capable of connecting all vessels within vicinity (10-mile range) make it pos-sible to share data and high quality video and offer VoIP. Rather than each vessel having to rely on individual satellite links, they can communicate with all vessels in the network and have a single satellite link or, if available, a fiber optic link from a nearby plat-form, backhauling data back to shore. All of these technologies, gizmos and widgets will never find use offshore if they don’t help accomplish their task more effi-ciently, with high reliability, and most importantly, safely. ON&T April 2011 Volume 17 • Issue 3 33

Severn Trent
Using a screen reader? Click Here