Tweaks improve Ocean Cleanup performance, but new issues rise

After six weeks of testing, the nonprofit Ocean Cleanup group has decided to use a parachute anchor system to slow down its plastic pipe-and-skirt contraption designed to collect marine litter from the Great Pacific Garbage Patch.

The new plan will allow System 001/B to achieve a consistent speed to capture plastic for eventual removal and recycling, according to an Aug. 16 website update from the Delft, Netherlands-based group.

The U-shaped system, which has been likened to an ocean rake, consists of a 525-foot-long floater pipe made of high density polyethylene and a detached polyester screen that captures plastic debris to a depth of 10 feet. The parachute anchor lets the system catch plastic and concentrates it against the screen, according to the Ocean Cleanup website.

The group had tested speeding up the system using large inflatable buoys. But using a parachute anchor to slow down the system allows wind and waves to push the plastic into the system.

"In the slow-down configuration, we haven't witnessed a negative speed differential at all, with plastic always arriving through the front, but never drifting out of the opening again. Hence, this is the concept we'll be moving forward with," the update says.

However, the group is encountering another problem it calls "overtopping." Some plastic is crossing over to a space between the pipe and screen. Now this issue needs to be solved before plastic is effectively retained.

In the original cleanup system, the screen was attached to the floater pipe but a stress crack formed at a welding point and a section broke away after only two months in the harsh ocean environment. The contraption was redesigned by detaching the skirt and bringing it forward using a cork line, something like what is used to section off a swimming pool, to hold the screen in place and prevent it from going slack.

The modification has proven mostly effective, but it creates a space between the screen and the floater that the group dubbed "the twilight zone."

"If you're familiar with the popular TV series, you'll know, there's always a twist in each episode; well, here's ours: the plastic is currently able to cross over the cork line into the 'twilight zone,'" the update says. "While it is technically still within the boundaries of the system, there is no screen underneath the floater pipe, so we cannot consider this plastic caught because it is not securely retained in front of the screen."

This problem seems like it will be easier to solve than the speed inconsistency issue, the group says. It plans to "massively" increase the buoyancy and height of the cork line. The update says the modified line will have three rows of floats stacked on top of one another, reaching a height of about 1 1/2 feet.

"Production has now been completed on this modification; it is currently on its way to the patch and we expect it to arrive soon," the Ocean Cleanup group says, adding that more tests will be done.

If it works, the contraption will be more like an ocean rake, according to the group, whose original plans were often compared to a PacMan gobbling up plastic.

"To clear the lawn, one could pick up the leaves one by one, which would take forever, or one could use a rake to concentrate the leaves into one big pile, to then pick up the pile in one go," the update says. "This is the main principle behind our cleanup concept; yet, our 'rakes' need to be able to survive for years in one of the harshest environment on this planet, while being able to hold on to the concentrated plastic without human aid."

The Ocean Cleanup's mission is to passively rid the world's oceans of plastic, starting with the Great Pacific Garbage Patch, which is located between California and Hawaii. The patch is the largest accumulation zone of plastic in the world, with debris spread out over an area twice the size of Texas.

The Ocean Cleanup says its focused center is five times farther away from land than the altitude of the International Space Station from Earth, making it an extremely expensive destination for the group, which has raised money from philanthropic, commercial and governmental donations and sponsorships.

Also, overtopping might not be the only problem left to solve. The system will need to be optimized for cost and scaling up to meet the Ocean Cleanup vision for a fleet of systems capable of cleaning at least 50 percent of the patch every five years.

"Yet, it is safe to say that we are closer than ever to having a tool capable of cleaning up these garbage patches for good," the update says.