The much-lauded cleanup system deployed to the Great Pacific Garbage Patch to collect plastic waste is returning to port in Hawaii earlier than planned after experiencing a bit of a problem. Just a few months after being launched, the passive floating system is catching plastic like it's supposed to, but an 18-meter end section has broken apart from the rest of the system.
Developed from a concept by Boyan Slat, the system was created by Ocean Cleanup, a Netherlands-based group that Slat leads. Dubbed 001 or Wilson, it consists of a 2,000-foot (600 meter) U-shaped boom with an attached woven skirt. It acts like a floating artificial coastline. The boom prevents plastic from flowing over it, while the skirt stops debris from escaping underneath it.
The offshore crew noticed on Dec. 29 that the section was detached but said it's too soon to say what exactly caused it to break though they have a suspicion. "We hypothesize that material fatigue (caused by about 106 load cycles), combined with a local stress concentration, caused a fracture in the HDPE floater," the group explained on its website.
Although the section is detached, the main section and end section are both stable, bulkheads are intact and no materials have been lost, according to the site. However, the boom must return to port now because both end sections have sensors and satellite communication have been compromised.
While this setback wasn't expected, the team is still hopeful.
"We are, of course, quite bummed about this as 1) we hoped to stay out for a bit longer to collect more data on plastic-system interaction, and 2) it introduces an additional challenge to be solved. At the same time, we also realize that setbacks like this are inevitable when pioneering new technology at a rapid pace. Being in port provides us with the opportunity to make upgrades to the system with the aim of solving the plastic retention issue, which we previously reported."
Late last year, the boom was struggling in places to hold on to plastic that it gathered.
"It has been four weeks since we deployed System 001 in the Great Pacific Garbage Patch (GPGP). In this time, we have observed that plastic is exiting the system once it is collected, so we are currently working on causes and solutions to remedy this," Slat posted on the group's website in late November. " Because this is our beta system, and this is the first deployment of any ocean cleanup system, we have been preparing ourselves for surprises."
In the video below, Arjen Tjallema, the group's technology manager, explained, "Plastics are entering the system but what we also see on some occasions plastics also leave the system again."
"Although we are not harvesting plastic yet, based on the current results, we are positive we are close to making it work," Slat says.
A question of speed
In early October, the group finished several weeks of testing System 001 and confirmed its "general behavior and seaworthiness."
One reason the system may not be working as hoped has to do with speed. In order to catch the plastic, the system typically has to move faster than the plastic it's hoping to catch, Slat points out. It appears that the system is moving too slowly.
"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. This motion counteracts the force of the wind, and, therefore, slows down the system," Slat writes.
"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 as it nears the mouth of the system."
Finding an answer
For a while, the team believed a solution was to open the U-shape in the system about 60 to 70 meters wider.
"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.
The extension will be performed in several stages until it reaches the desired effect. Opening the U is expected to affect the system's ability to pivot quickly when the wind changes direction, so it's key not to widen it too much, according to Slat.
"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."
Now that System 001 has a broken end section, there is no update yet from Ocean Cleanup whether or not their solution of expanding the boom will still happen after the repairs are made or when the boom will go back out to the Great Pacific Garbage Patch.
Editor's note: This article has been updated since it was originally published in December 2018.