Sea Technology

AUG 2013

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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(Top) AUVs and ROVs can carry sonars for visual inspection of the structures and are not affected by turbid water conditions. (Middle) The Bluefn Hawkes ROV (U-4000) can stationkeep in currents of up to 6 knots. (Bottom) Onboard tether and power system allow for a tether diameter of less than 4 millimeters, and the entire system can be mobilized out of a 40-foot transportable ISO container. stallations have historically occurred in waters of 20 meters or less, although there is a trend in offshore wind to drive to deeper water depths. OTEC technologies generally occur at a sea wall, where cool water from very deep locations (1,000 meters or more) is pumped to a shallow location for thermal energy conversion. The very nature of MHK and offshore wind installations fnds them located in environments where wind, waves, tides and currents are consistently energetic enough to make conversion into electricity both viable and, ideally, cost-effective. While benefcial from an energy standpoint, these locations can be extremely challenging from an installation and maintenance perspective. Modern ROVs used for support cannot sustain stationkeeping beyond approximately 2 knots, far below the currents of up to 6 knots observed in some candidate deployment areas. In addition, the strong winds and high tidal and ocean currents found in littoral waters favored by these technologies are often accompanied by extremely poor water clarity. The primary sensory feedback, video data, is obscured to the point of rendering divers or ROVs useless in certain conditions. This leads to costly delays while the support resources wait for favorable conditions to resume operations, despite support vessels being more than capable in surface environments. Support activities for MHK and offshore wind installations can be grouped into four main categories: initial site survey, installation, cabling, and both fnal and maintenance surveys. These support operations require a variety of subsea assets on site to execute the installation and maintenance, ranging from specialized vessels to commercial divers to towed-survey sleds to ROVs. Such operations are often both time consuming and expensive. While MHK and wind turbine installations are relatively shallow, high currents can reduce the effectiveness of towed systems and ROVs, and reduced visibility can challenge the effectiveness of divers. Robotic systems, such as AUVs and innovative ROVs, can address these challenges by providing highly accurate survey capability and ROV station-keeping in high-current environments with forward-looking sonars such that the operational availability is signifcantly higher than has been observed to date, reducing overall installation costs and improving the cost-effectiveness of the system over its lifetime. Bluefn Robotics AUVs The Bluefn Robotics AUVs are versatile systems that can be used for a wide range of survey types. For shallow or deep survey applications, the Bluefn-21 is a capable, confgurable tool that can obtain high-quality data from an array of oceanographic sensors. It can maintain sensor positioning at an ideal height, between 10 and 50 meters, above the seafoor during surveys, is unaffected by surface sea states and can follow a rough terrain to produce the best possible images— August 2013 / st 11

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