Ocean Cleanup Device Catches, But Does Not Retain Plastic

Since deploying Ocean Cleanup System 001 in the Great Pacific Garbage Patch (GPGP), the project team observed that plastic is exiting the system once it is collected.

In a statement from the project, they said that they were working on causes and solutions to remedy the issue. Because this is a beta system, and this is the first deployment of any ocean cleanup system, they say that they have been preparing for surprises. Although the deployed device is not harvesting plastic yet, based on the current results, the Ocean Cleanup team says, “We are positive we are close to making it work.”

They were not the only ones to expect problems. An ECO Magazine article published in 2015 shared both criticisms of the plan and the Ocean Cleanup team’s response. Based on their observations from this beta deployment, the team now says that they plan to “tune the system . . . and not just collect, but also retain the plastic caught.”

Initial Observations from the Ocean Cleanup Team

On October 6th, the Ocean Cleanup team completed the Pacific Trials 350 nautical miles from land, through which they confirmed the system’s general behavior and seaworthiness.

After giving the go-ahead to continue the remaining 850 nautical miles to the GPGP, the team deployed System 001, or Wilson, in its operational configuration. There has been one crew change since the launch, which brought in a new set of team members with different objectives. The main goal of Crew 1 was to deploy and install Wilson in its U-shape, and, now, Crew 2 is focused on observation, data analysis and, soon, plastic collection. These have been their main, initial observations:

• For the most part, the system is behaving as predicted
• Plastic density in the GPGP is in line with our expectations; but, due to our short time in the GPGP, this is a limited data set, so we cannot fully verify this yet
• No interactions with marine life have been observed
• Small particles float within the system, though quantitative measurements are still required
• Plastic remains in the system for a relatively short time

Cause and Effects

Although the technology is built on simple principles, the dynamics are complex. There could be various reasons why plastic is not staying inside the system. We have concluded that the system does appear to be moving too slow at times (remember, to catch the plastic, we need a speed difference where the system is faster than the plastic) or, occasionally, the speed difference appears to be reversed, where the plastic is then faster than the system. At the very minimum, the system needs to be continuously traveling faster than the plastic.

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.

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. The team says that they believe the first solution they will attempt could potentially remediate both of these causes.

Solution

The Ocean Cleanup team has conducted scale model tests and created computer models, and, yet, this phenomenon was never observed, so they have not had a solution ready to deploy. However, they felt that the first logical solution could be easily-enacted because they had the materials available on board the vessel.

The team addressed the speed difference by opening the U-shape about 60-70 meters wider. Doing this, they thought, would have two effects on the speed of the system; firstly, it would 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, the team thought 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.

To perform the extension, the team lengthened the closing lines which keep the cleanup system in its U-shape. They performed the extension in several stages. As an increased span was expected to have a negative effect on the system’s ability to rapidly pivot when a change in wind direction occurs, the team had to be careful to not increase the span too much.

Results of the First Solution

On 4 December, the Ocean Cleanup team reported that the closing line extension did not effectively increase the span of the system and, therefore, the speed did not improve. Further approaches to widen the u-shape are being evaluated and tested by the team.

What’s Next

System 001 must work before the Ocean Cleanup team can look to scaling up, so there is no time to waste. They continue to analyze more data and test alternative solutions until the system is fully operational. To follow the team’s efforts to implement a solution to this snag, visit.