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The Ocean Cleanup System Needs to Speed Up

By The Maritime Executive 2019-04-01 18:42:52

In September last year The Ocean Cleanup launched its first ocean plastic cleanup system after completing hundreds of scale model tests - only to find that while it collected and concentrated the garbage, it was not retaining it.

The system, named System 001 or Wilson, should have been able to retain debris for several weeks or even months, since that will be the expected timeframe between collection trips. 

A root cause analysis showed that the relative speed differential between the plastic and the system occasionally shifts from positive to negative. For the system to effectively retain plastic, it must consistently travel faster than the plastic.

The solution that the system's engineers have arrived at is to open the U-shape about 60-70 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, widening the span could also reduce the propulsive force caused by the undulating ends, because it would not be directed straight into the motion direction of the system anymore.

Whilst in the the Great Pacific Garbage Patch, the system also suffered a structural failure, causing an 18-meter end section to disconnect from the rest of the system, just before the end of 2018. This proved to be a fatigue issue, relatively easy to fix compared to the garbage retention issue.

However, many aspects of the technology were validated:

• The U-shape configuration (and the system's ability to retain the U-shape). Once the system was arranged in its operational shape, it maintained this configuration without any challenges.

• System 001's ability to orient with the wind. To be able to effectively catch plastic, the concave side of the system must always point in the direction the system travels (relative to the plastic). Hence, the system was designed to be able to passively orient itself away from the wind, and it did exhibit this self-orienting behavior.

• Plastic concentrations in and around the system were much higher than in any other location in the Great Pacific Garbage Patch; and, although the periods the plastic was retained in the system were not yet of sufficient length, the system did capture and concentrate plastic. 

• Due to the heterogeneity of ocean conditions, System 001 was built to follow the varying movements of the water, rather than respond against the forces. The system's stability in operational configuration and response to following the waves were in line with design expectations.  

• Plastic was not witnessed to have been lost due to over-topping.

• During its time offshore, the electronics and the satellite connection were strong, crucial for a system that will ultimately be fully autonomous.

• During its deployment, no environmental impact issues were observed.

The system was demobilized in Hilo Bay, Hawaii, on March 23, 2019, and the team hopes to be ready for a relaunch within a matter of months.