This article presents an overview of a robotic system, named Hull BUG, designed to remove deposits from the undersides of ships. The robot is the product of SeaRobotics, a company in Palm Beach Gardens, FL, USA, that develops unmanned vessels for jobs including deep-water research and coastal surveillance. The current developmental model of the Hull BUG uses a negative pressure vortex regenerative fluid movement assembly to attach itself to the hull. The robot is designed to work without using cleaning chemicals. It measures about 2-feet wide, 2-feet long, and 1-foot high. Weighing 30 pounds, it is designed to be neutrally buoyant in seawater, so it needs less propulsion to negotiate a ship’s hull underwater. The Hull BUG requires no human operator. Onboard sensors provide obstacle avoidance, path planning, and navigation capabilities. These capabilities include a biofilm detector that can distinguish between fouled and groomed surfaces. The Hull BUG has already been tested on many pieces of steel having different types of structures and shapes to model sections of ship hulls.
A ship is a graceful, often inspiring sight, especially as the sleek hull knifes through the water with speed and efficiency.
But sleekness is constantly becoming compromised in seawater, because ship bottoms become covered with bumps and film as marine life latches onto surfaces below the waterline. Then the vessel does not go so easily. Biofouling—a buildup of oysters, barnacles, and algae on the hull—creates resistance in the water that can increase a vessel's fuel consumption by as much as 40 percent and can cost a ship as much as 10 percent of its speed.
When you operate as many ships as the U.S. Navy does, you can save a great deal of money by keeping your hulls well groomed. What's more, high-performance naval warships and submarines rely on critical design factors such as high speed, acceleration, and hydroacoustic stealth to achieve their missions. All of these properties are reduced by the growth of biological organisms on hulls.
That's why a development program at the Office of Naval Research has been looking closely at a new robot designed to remove deposits from the undersides of ships. The Navy describes it with the phrase “robotic hull bio-inspired underwater grooming,” so it can call the machine “Hull BUG.”
The robot is the product of SeaRobotics, a company in Palm Beach Gardens, Fla., that develops unmanned vessels for jobs including deepwater research and coastal surveillance. According to the company's president, Don Darling, “We designed and developed the Hull BUG based on a proposal we submitted to the Navy.” The Hull BUG prototype is currently in its third generation.
Steve McElvany, program officer in the Office of Naval Research, said the current developmental model of the Hull BUG uses a negative pressure vortex regenerative fluid movement assembly to attach itself to the hull. Several mechanisms, including rotary brushes and specialized water jets, are being considered to groom hull surfaces. A suite of sensors onboard the robot will let it navigate the undersurface of the ship and give it the ability to distinguish fouled from clean surfaces.
Biofilms build up when ships sit motionless in port, where U.S. naval vessels spend about half their lives. According to the Naval Surface Warfare Center, Carderock division, at West Bethesda, Md., biofilms on Navy vessels cost U.S. taxpayers about $500 million a year. The cost of biofouling to the commercial shipping industry is large but unknown.
It is costly and time-consuming to lift a large ship out of the water to clean it below the waterline, so drydock maintenance can’t be done very often. And that's where the Hull BUG comes in.
It is a promising alternative to the use of toxic hull coatings or cleaning chemicals harmful to the environment. Recent regulations have removed the most effective biocidal coating, TBT self-polishing copolymer paint, from the market because of its harmful environmental effects. There is no other commercial coating providing similar effectiveness.
The robot is designed to work without using cleaning chemicals. And the Navy hopes that it can extend the period of time between costly dry-dock maintenance procedures.
“The best way to stop barnacles from colonizing is don’t let them settle and colonize on the hull in the first place,” McElvany said. The Hull BUG removes barnacles, oysters, algae, and other marine life from ships’ hulls before extensive growth has a chance to occur.
If it is used to groom ships in port, the Hull BUG will remove the biofilm and other marine organisms before they become solidly attached.
Geoff Swain, professor of oceanography and ocean engineering at the Florida Institute of Technology, oversees ONR's Hull BUG testing. He calls his findings on biofilm removal “very exciting results.”
The Hull BUG has been tested on many pieces of steel having different types of structures and shapes to model sections of ship hulls. Swain performed his tests in seawater in a large testing pool at Florida Tech.
According to Swain, the robot was also tested on a portion of a cruise ship's hull. “The Hull BUG autonomously groomed and removed biofilm from an area on the port midship section of the hull in a preprogrammed pattern,” he said.
In developing the robot, engineers had to make it work on the nearly vertical sides of ship hulls and also work upside-down on the bottom of the hull. For environmental reasons, the Navy wanted it to clean without using chemicals.
The Hull BUG measures about 2 feet wide, 2 feet long, and 1 foot high. Weighing 30 pounds, it is designed to be neutrally buoyant in seawater so it needs less propulsion to negotiate a ship's hull underwater. The Hull BUG will operate off batteries most of the time. Power is needed to both propel and steer the wheels. Movement is generated by an independent drive on each wheel.
Power also is needed for the vortex device that holds the Hull BUG to a ship's hull and to operate the robot's grooming devices.
“Magnetic wheels were considered as a means of keeping the Hull BUG attached to the bottom and vertical sides of a ship's hull,” McElvany said. “However, the Navy is investigating the development of composite hulls made of advanced plastic composites. Magnetic wheels would not be attracted to a composite hull.” Heavy buildup of barnacles and other bio-deposits would weaken the attraction of magnetic wheels to a steel hull.
The Hull BUG requires no human operator. Onboard sensors provide obstacle avoidance, path planning, and navigation capabilities. These capabilities include a biofilm detector that can distinguish between fouled and groomed surfaces.
The biofilm detector uses modified fluorometer technology to enable the robot to tell the difference between clean and unclean surfaces. A fluorometer is a device that detects fluorescence after irradiating a surface with ultraviolet light. It can be used to detect the presence of biological molecules—that is, the presence of biofilm— without the intervention of a human operator.
Being able to detect these differences tells the robot when and where to activate its rotating brushes and groom the hull.
By combining the Hull BUG with newly developed, environmentally benign antifouling hull coatings “the Navy will save millions of dollars per year in fuel,” McElvany said. “Using less fuel also means less carbon dioxide in the atmosphere.”
It may be 2015 before the Hull BUG gets to groom an actual sea-going Navy vessel. According to Darling of SeaRobotics, “We recently completed a three-year contract and have received a second three-year contract for next-phase testing. This will cover in-water tests on ships.”
McElvany said the Navy plans to use two robots per ship. Grooming time per ship will be about one month, probably longer for aircraft carriers and large cruisers.
The technology is probably not practical for ships shorter than 45 feet, which are easily removed from the water for conventional cleaning. Also, ships smaller than 45 feet have more sharply curved hulls than larger ships. The sharper curvature makes it more difficult for the vortex device to strongly attach the Hull BUG to the hull.
The robot's benefits could extend beyond the Navy. As Ken Holappa, a SeaRobotics engineer, sees it, “Just like the Navy, the savings to the commercial shipping industry stand to be significant in terms of fuel efficiency and in reducing emissions associated with ship operations in our world's oceans.”
According Darling, “Basically any boat over 45 feet, which is in the water all the time, can benefit from this kind of technology.”
The Navy sees other uses for the technology, too. According to ONR, the Hull BUG platform could be used to develop other capabilities such as ship hull inspection or defensive duties, such as the detection of mines or other sabotage devices attached to ship hulls.