A passive cleanup system for marine debris that was deployed to the Great Pacific Garbage Patch is being fine-tuned after a month at sea because some plastic is eluding it.
Developed by the Netherlands-based non-profit group called Ocean Cleanup, the system consists of a 2,000-foot-long high density polyethylene boom with a polyester woven skirt attached to the underside to gather plastic from the surface to a depth of 10 feet.
The boom is supposed to float on the waves and keep garbage from flowing over it as the drag on the tapered skirt forms a U-shape to collect plastic like a Pac-Man gobbling dots.
Considered the world's first large-scale ocean cleanup system, the crowd-funded contraption reportedly proved seaworthy, kept its U-shape, moved through the water at sufficient speed, and reoriented itself with wind and wave changes during a two-week trial period in the Pacific Ocean.
The system then was pulled by tug boat another 850 nautical miles to the garbage patch, where Ocean Cleanup says some plastic slips away after just a short time.
"Plastics are entering the system but what we also see is that on some occasions plastics also leave the system again," Arjen Tjallema, the group's technology manager, says in an online video about the problem before engineers.
In his recent update, Ocean Cleanup founder Boyan Slat said, "Although we are not harvesting plastic yet, based on the current results, we are positive we are close to making it work."
The system apparently isn't traveling faster than the plastic at all times.
"One hypothesis is that the force of the wind against the system might be making both extreme ends of the floater pipe oscillate (like the fin of a fish), which may lead to a motion force against the wind direction," Slat said. "This motion counteracts the force of the wind, and, therefore, slows down the system. It is also possible that the vibrations in the ends of the U-shape could be creating a type of ripple-force field that repels the plastic away from [it] as it nears the mouth of the system."
A monitoring crew is addressing the speed difference by opening the U-shape another 60-70 meters using materials aboard their vessel.
"Doing this should, theoretically, have two effects on the speed of the system; firstly, it will increase the surface area of the system exposed to the wind and waves, which are the driving forces of the system. Secondly, by widening the span, we think this could also reduce the propulsive force caused by the undulating ends, simply because it would not be directed straight into the motion direction of the system anymore," Slat says in his update.
The group is extending the closing lines in several stages.
"As an increased span is expected to have a negative effect on the system's ability to rapidly pivot when a change in wind direction occurs, we must be careful to not increase the span too much," Slat said.
Dubbed System 001, the marine debris cleaner is the culmination of five years of research, prototyping and fundraising that generated about $35 million in donations and sponsors, including PayPal co-founder Peter Thiel.
Ocean Cleanup members worked with experts at Agru GmbH and its Georgetown, S.C.-based Agru America Inc. subsidiary to develop a buoyant and flexible HDPE boom to hold up against harsh ocean conditions.
"System 001 must work before we can look to scaling up, so there is no time to waste," Slat says. "While we are busy implementing this first solution, our team is continuing to analyze more data and test alternative solutions until the system is fully operational."
In the online video about the changes being made to optimize the system to reach its full potential, Slat says the group is closer than ever to success and he's confident it will eventually work. The overall goal is to haul the harvested ocean debris ashore for recycling into new products.
