Autonomous Hull Grooming Vehicle
AREA(S): Ground/Sea Vehicles, Materials/Processes, Sensors
PROGRAM: NAVSEA 05P5 Shipboard Environmental Afloat 6.4 Program
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
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
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.
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:
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
Physical Constraints, Dimensions, and Weight:
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:
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.
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
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.
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
(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.
II: (Phase II Base):
Develop initial tasking for actual vehicle implementation around a qualified
sensor and instrument suite that would encompass software and hardware
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
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
(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
-- 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
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.
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
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
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&.
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
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,
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/).
Autonomous Underwater Vehicle (AUV); Hull Grooming; Biofouling; Sensors;
Underwater Navigation; Hull Husbandry
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