Untethered AUV'S Can Reduce Costs For Offshore Inspection Jobs
Authors: Collins Ken 
Published: October 2008

ABSTRACT
Applied Remote Technology (ART) has been developing autonomous underwater vehicles since the early 1980's. This maturing technology can now provide economical solutions to a variety of subsea tasks in the offshore oil industry. Low-drag, untethered, self-powered vehicles allow faster transit speeds and independence from surface support ships and weather conditions. This equates to significant reductions in operational costs when compared to tethered ROV operations for most large-area jobs. A gradual transition is presented for gaining independence from the present-day man-in- the-loop control. A future is explored in which AUVS will be deployed from an operations base to "go do their jobs" and return, without requiring the expense of full-time operators or support vessels AUV design concepts are presented for pipeline inspection, site bathymetry survey, and geophysical exploration. This paper concludes by describing the enhanced A UV capabilities that will soon be available with large-area Laser viewing sensors and Iong-endurance aluminum-oxygen fuel cell power systems.

INTRODUCTION
Government and industry research has developed a variety of autonomous undersea vehicles (AUVS) to perform subsea tasks free of bulky tether cables. This paper discusses the existing capabilities and realistic work potential for the 21 -inch diameter AUV, known as XP-21, shown in Figure 1. This AUV has been refined and upgraded during four years of operational dives in the ocean off San Diego deployed from its support vessel, shown in Figure 2. AUV engineers apply proven remotely operated vehicle (ROV) technologies and experience to evolve tetherless vehicles with new capabilities AUVS are now ready to demonstrate their cost advantages offshore.

OPERATIONAL ADVANTAGES OF AUVS
AUVS are independent of surface support and can transit faster than ROVS, thus requiring reduced vessel time and crew. The lack of a heavy tether to power an AUV eliminates expensive and high maintenance cable handling equipment. With its optimized low-drag shape and no cable drag, the XP- 21 AUV can propel itself at 6 knots with only 2 horsepower of thrust. Without any physical connection to the vehicle, the surface vessel's navigation watch circle is more relaxed and the submerged vehicle is not jerked or towed astray by the tether. An AUV can maneuver freely under acoustic control with a large horizontal offset from the operator. Below the surface, vehicle operations do not need to be interrupted due to bad weather because the AUV is unaffected by wind and sea conditions. The freedom from tethers also allows faster transits and surveys, independent of water depth, for more time-efficient project completions. Another advantage of AUVS over ROVS is their increased level of automation that requires only supervisory operator control. AUV operations require fewer crew members because they are less fatiguing for pilots; and the overall job success is less dependent on operator skills. Once operational experience builds trust in AUVS, many tasks will be performed without the need for costly surface vessel support or personnel. For even greater cost savings, AUVS, alone or in "teams" will begin and end their dives from multi-function surface vessels, offshore platforms, or shore facilities.