TECHNOLOGY AREA(S): Ground/Sea Vehicles, Materials/Processes, Sensors

ACQUISITION PROGRAM: NAVSEA 05P5 Shipboard Environmental Afloat 6.4 Program

OBJECTIVE: The goal is to develop a tethered, autonomous hull-crawling vehicle that supports and optimizes grooming operations on ship hulls while in port.� The focus is on the development and integration of novel on-board sensors and methods to optimize coverage and navigation without the need of manned operations.

DESCRIPTION: Biofouling increases hull roughness and drag, negatively impacting vessel operations and fuel efficiency.� The DoD propulsive fuel expenditures exceed $2B annually.� Up to 15% of the fleet's propulsive fuel costs are wasted in overcoming the effects of drag from biofouling.� Currently used biocide-based coatings become fouled in 1-2 years and require periodic underwater hull cleanings.� Proactive hull grooming (removal of early stage biofouling on a weekly basis) keeps the hulls fouling free and ships at full operational capability.� This effort will build upon existing grooming methods and hull attachment (brushes and/or non-magnetic attachment) to develop a highly autonomous vehicle through integration of a variety of sensors (e.g., depth/gravity-vector, odometry, sonars etc.) into an affordable platform that provides accurate navigation/coverage of the grooming process (the highest risk area of the grooming approach at present) and requires only minimal human operational oversight.� Hull grooming is projected to significantly extend the intervals between diver-based hull cleanings and generate significant fuel savings in the interim to offset any additional acquisition and operating costs over current operations.

Vessels of interest for autonomous grooming in the near term would be DDG-51 (Arleigh Burke Class Destroyer) and both variants of the Littoral Combat Ship (LCS).� The wetted surface area of a DDG-51 is approximately 32,000 square feet.
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Large panel grooming tests on both copper ablative anti-fouling paints and biocide-free silicone-based foul release coatings indicate that grooming the hull once a week is generally sufficient to control the marine biofouling.� The grooming frequency required to prevent the development of hard and most soft (biofilm) fouling was determined to subject the coatings to an acceptable level of impact with regard to wear and damage to the coatings from relatively soft rotary brushes of the grooming tool including the effect of any entrained solids removed from the hull during the process.� Any areas that are missed during a grooming cycle increase the probability for biofouling to develop beyond early settlement; hence, there is a dependence on good navigation and positioning to ensure coverage and long-term efficacy.

Concepts of operation have nominally converged on a two-foot wide grooming swath with 50 percent overlap and a path speed of 0.5 foot per second; as such a reasonable resolution for repeatable positioning to ensure proper grooming coverage is plus or minus six inches.� As described above, the grooming path progress for operation would facilitate the grooming of 75 percent of a DDG-51 covering 24,000 square feet of underwater hull areas forward of the running gear in 16 to 17 hours.� This in turn could be extrapolated to a single tethered autonomous grooming system being shared across two DDG-51 class vessels for a once a week grooming cycle.� (See: Nominal Autonomous Grooming Vehicle System Requirements near the end of this section.)

Grooming operations would likely entail multiple vehicles servicing multiple vessels in close proximity to each other in what is often a shallow noisy environment with very poor visibility.� Beyond coverage for grooming efficacy, the autonomous tethered vehicle will need to avoid hazards presented by various hull structures (e.g., sea chests, bilge keels and other obstructions or areas to be avoided); the vehicle system in particular will have to rely on positioning to manage its tether to avoid entanglement.

Any technical approach proposed for autonomous grooming needs to be viable on vessels of all material types; these presently being hulls of steel, aluminum, and various composites.� Naval operations prohibit the use of magnetic attachment methods.� Proposed vehicles should incorporate negative pressure impeller-based attachment and/or the use of attachment provided by the rotating brush forces.� Development of new attachment approaches should not be a focus of this effort.
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Proposals should describe how the risks of using a tether in an autonomous system will be mitigated.� It should be noted that a tether may present some entanglement risk; however, the tether itself presents an opportunity to remove or reduce several operational constraints with regard to power, endurance, and communications bandwidth to and from the surface.

NOMINAL AUTONOMOUS GROOMING VEHICLE SYSTEM REQUIREMENTS:

Mission Path Performance Guidelines:
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Vehicle On-Hull Path Velocity: ~ 0.5 ft./sec (30 ft./minute)
Physical Tool Grooming Tool Width: ~ 2.0 ft. Average
Grooming Overlap: 50 percent of Tool Width
Average Effective Grooming Swath: ~1.0 ft.
Average productivity rate for area groomed: ~30 square feet per minute
Positioning Repeatability: +/- 6 inches along any axis in local plane of the hull

Physical Constraints, Dimensions, and Weight:�
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Vehicle Weight: approximately 150 lbs.
Vehicle length: approximately 48 inches, inclusive with Grooming Tool
Vehicle Width: approximately 30 inches
Vehicle Height: approximately 24 inches.
Tether Length: 100 meters

Grooming System General Requirements:
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Grooming frequency is anticipated to be once a week without undo repetition along prescribed path areas to minimize impact on hull coating.� Areas to be groomed autonomously will generally make up approximately 75 percent to 80 percent of wetted surface comprised of non-complex, underwater hull surfaces forward of the running gear.

Data logging should at minimum allow for power monitoring and status for major facets of vehicle operations such as the grooming tool, locomotion including vehicle to hull attachment, and tether management.� Data logging for navigation will be a tool for quality control to insure adequate coverage for efficacy without excessive impact on the hull coating.

PHASE I: (Phase I Base):

The proposer will identify candidate sensors and instrumentation (or identify gaps in sensors needed to be developed and approaches thereof for Phase II efforts) for relative positioning and navigation as a prerequisite task for developing a tethered autonomous hull grooming system that has to operate in shallow noisy underwater conditions of low visibility�as little as several inches�such as Norfolk, VA where turbidity often constrains divers to operate by feel.

With regard to acoustic interference, there are typically noise sources that range in frequency from few hundred hertz to in excess of 150 KHz; and these generally originate from shipboard machinery, propeller noise, and biologics such as snapping shrimp.� The environment being shallow, reverberation and multipath issues present additional challenges for any acoustic-based schemes to be employed.
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Consideration must be given to the cost, complexity, and underwater durability of sensors in addition to the skills and time required for setup and initialization.� Throughout system design and development, attention also should be given to minimize power requirements for all components as future efforts may examine the possibility of using on-board power.

The objective of identifying a proposed sensor suite early in the effort will be to increase the overall understanding of the positioning related limitations for autonomous hull grooming.� Generating initial figure of merit for best- and worst-case performance for any sensor suite scheme is critical prior to making any large investment in control software, vehicle hardware, and engineering design efforts in Phase II.

Additional objectives for this phase are to describe how the proposed suite of sensors and instrumentation will be coordinated to provide the autonomous guidance and control of the vehicle that must avoid hazards and negotiate obstacles on the hull.� This may include obtaining preliminary laboratory-based measurements of proposed sensors and instrumentation to provide data to determine reliability/accuracy and to identify sensor gaps.

The primary deliverable will be a report fully describing the sensors and instrumentation for use in repeatable positioning on the non-complex areas of the hull, forward of the running gear.� Additionally, the report should include a preliminary design and cost estimate for the proposed vehicle to be developed in Phase II.� Eventual cost, complexity, and durability of the sensor/navigation suite is of primary consideration as these vehicles/systems will be widely used in a continuous concept of operations on ships while in port.

(Phase I Option):

Leveraging on the results of the Phase I Base tasking, would be to further define a detailed design and cost plan for vehicle development and sensor integration.� Any concerns involving tether management should start being considered in the option phase along with developing plans for addressing sensor gaps that are not addressed by COTS items in Phase I.

PHASE II: (Phase II Base):

Develop initial tasking for actual vehicle implementation around a qualified sensor and instrument suite that would encompass software and hardware development.

The principal milestone under Phase II would be the demonstration of closed loop autonomous control for relative positioning from primary reference fixes established on the hull.� Being a tethered test bed system, it will be acceptable for the control loop to be closed and monitored by a computer control station at the surface.� Early Phase II work should determine the accuracy and coverage that can be obtained with simple on-board sensors and associated integration and software which can then be used to identify the extent and complexity of additional external positioning/referencing or feature-based navigation capabilities that are required to provide the desired capabilities for optimum grooming operations of the vehicle.

The tasking will include demonstration test sequences at various locations on the hull that would subject the vehicle system to a full range of attitude and heading orientations along with avoidance of obstacles to fully exercise the sensor suite and control software.� It is well expected that the hull surfaces being groomed will range from near vertical to horizontal with some oblique orientations in between�all typical of locations on the hull near the turn-of-the-bilge.

If funding and time permit in Phase I, efforts on developing additional advanced navigation/location capabilities to complement on-board sensors can be initiated.� Autonomous acquisition of hull features to establish primary reference fixes is highly desired for operational capability.� However, an interim demonstration of autonomy with navigation and control by relative positioning can be performed after primary reference points on the hull have been acquired and established as �known good� fixes by the operator with the vehicle under manual control at various locations on hull.� Autonomous control capability needs to be demonstrated through a full range of attitudes and vehicle headings.� �Known good� is a navigation term generally denoting quality of a fix as absolute or usable with high confidence.

Primary deliverable will be a sensor and instrument equipped tethered vehicle system capable of accommodating (but not yet integrated with) a grooming tool capable of providing the described hull coverage.� The completed delivery will also contain reporting on the system design and testing with copies of the software required for autonomous vehicle system operation.� Documentation and descriptions of the system software developed are likewise considered a deliverable.

(PHASE II Option):

The primary goal under Phase II Option tasking is to complete any advanced navigational capabilities and demonstrate a fully integrated autonomous vehicle capable of being deployed in a representative grooming mission.� The tethered vehicle from Phase II Base will now be fully equipped with a grooming tool and sensor suite capable of operating autonomously under closed loop control.

Beyond the tasking in Phase II Base above, it is additionally expected that the feasibility of completing sequential legs of grooming operations autonomously will be demonstrated with relative positioning alone.� Further capability for full autonomy would be met by demonstrating autonomous acquisition of �known good� fixed reference points on the hull to support control and navigation by relative positioning to again facilitate completion of sequential legs for autonomous hull grooming operations.

All features of tether management as integrated into the autonomous system will be demonstrated.� Field testing under the Phase II Option again needs to operate through a wide range attitude and heading situations to validate autonomous operations of a tethered grooming vehicle system.

A major goal is for operational requirements to be well understood in the following areas:

--� system setup, deployment, and recovery
--� level of autonomy achieved once on the hull
--� ability to negotiate obstacles and hazards without manual control
--� vehicle situation and mission progress monitoring
--� manual efforts as required establishing primary reference fixes
--� daily, weekly, and monthly maintenance
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The completed autonomous grooming vehicle system and final report are to be the major deliverables with the completion of the Phase II Option.� Requirements for reports, test data, and system software with software documentation and software descriptions are the same as for the deliverables under the Base section of Phase II.

PHASE III DUAL USE APPLICATIONS: Following any success on the DDG or LCS class vessels, hull grooming with autonomous or semi-autonomous tethered vehicle systems to control marine biofouling would likely expand to other ship classes and types in the U.S. Navy.� Similar opportunities for autonomous hull grooming are presented by the vessels of the Maritime Administration (MARAD), Military Sealift Command (MSC), U.S. Coast Guard (USCG), U.S. Army, and the University National Oceanographic Laboratory System (UNOLS).

It is additionally anticipated that commercial shipping and cruise line operators would pursue a similar approach to control marine biofouling.� Controlling marine biofouling on offshore structures for the oil and gas industry is another related opportunity.

Transition to autonomous hull grooming in any case has to be economically competitive with present diver-based practices for periodic hull cleaning to control marine biofouling and present minimal impact to the hull coatings employed.

Methods and technologies developed and advanced for navigation and control of an autonomous grooming vehicle are germane to hull survey and inspection applications with regard to reducing pilot work load for unmanned vehicle operations.

REFERENCES:

1. Hearin, John, Hunsucker, Kelli Z., Swain, Geoffrey, Gardner, Harrison, Stephens, Abraham and Lieberman, Kody. �Analysis of Mechanical Grooming at Various Frequencies on a Large Scale Test Panel Coated with a Fouling-Release Coating.� Biofouling (The Journal of Bioadhesion and Biofilm Research), 07 April 2016, p. 561-569. http://www.tandfonline.com/doi/abs/10.1080/08927014.2016.1167880?needAccess=true&.
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2. Tribou, Melissa and Swain, Geoffrey. �The Effects of Grooming on a Copper Ablative Coating: a Six Year Study.� Biofouling (The Journal of Bioadhesion and Biofilm Research), 12 June 2017, p. 494-504. http://www.tandfonline.com/doi/full/10.1080/08927014.2017.1328596

3. Schultz, M.P. (Dept. of Naval Architecture and Ocean Engineering, United States Naval Academy) and Bendick, J.A., Holm, E.R., and Hertel, W.M. (Naval Sea Systems Command, Naval Surface Warfare Center Carderock). �Economic Impact of Biofouling on a Naval Surface Ship. Biofouling, Vol. 27, No. 1, January 2011, p. 87-98.
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4. Johannsson, Hordur, Kaess, Michael, Englot, Brendan, Hover, Franz, and Leonard, John. �Imaging Sonar-Aided Navigation for Autonomous Underwater Harbor Surveillance.� 2010 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 18-22 October 2010. Digital Version published in IEEE Xplore 3 December 2010 (http://ieeexplore.ieee.org/document/5650831/).

KEYWORDS: Autonomous Underwater Vehicle (AUV); Hull Grooming; Biofouling; Sensors; Underwater Navigation; Hull Husbandry