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Taking out the trash

Ship & Boat International: eNews July/August 2020

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Dutch entrepreneur Boyan Slat hit the headlines several years ago when he founded The Ocean Cleanup (TOC), an organisation keen to eradicate the world’s marine garbage patches. The group’s first innovation, the Interceptor, has been developed to tackle the gyres directly, using a boom and a rubbish collection device. “We need to both clean up the legacy and close the tap, preventing more plastic from reaching the oceans in the first place,” Slat says. The Ocean Cleanup claims that just 1,000 rivers are responsible for 80% of all plastic entering the world’s seas.

 

The organisation’s answer is the Interceptor – and now it’s going to reach Jamaica’s worst polluted waterway, the Hunts Bay, which is responsible for an estimated 578,000kg of plastic flowing into the ocean each year, The Ocean Cleanup reports.

 

The 24m x 8m, crew-free Interceptor is akin to a barrier and conveyor belt system, designed to extract plastic from rivers. The Interceptor utilises the water’s natural flow to direct the rubbish along a boom. This only spans part of the water, leaving room for navigation and wildlife movement. Although it’s anchored in place with a four-point mooring system, the Interceptor’s main body has been developed with hydrodynamics in mind. The catamaran-style design allows the water to pass uninterrupted between the twin hulls.

 

The floating plastic is directed over a permeable, grid-type conveyor belt, which lifts it out and upwards onto an automated shuttle that measures its load and distributes the waste between one of six 8.3m3 containers sitting on a 14m x 4.5m barge between the hulls below. While the Interceptor remains unmanned, a person would be required to pilot the barge – though this part of the clean-up process may become remotely controlled or autonomous in the future.

 

A passive deflection system at the front of the Interceptor reduces the risk of large debris clogging or damaging the system. If a big lump gets through and blocks the extraction conveyor belt, the control systems will trigger a shutdown and notify the operator. As a result, the Interceptor can cope with a fair degree of plastic congestion. The maximum belt extraction rate can reach 24kg/sec – that’s a 200kg load on the conveyor belt, although it’s not the plastic itself; rather the partial fill of bottles, and so on, that pushes up the weight.

 

The Interceptor can extract 50,000kg of trash daily, doubling this volume under optimised conditions. The Ocean Cleanup says: “Unloading usually [takes place] around every day or two, or a couple of times a week”. Once the barge has left, the shuttle can still act as a buffer, allowing trash collection to continue while it’s away on a disposal run.

 

Barge dispatches aside, onboard power demands are low. Subsequently, all electronic demands aboard the Interceptor can be met by the 5.6kW photovoltaic cells that cover the top of the vessel and charge a 20kWh lithium battery. This allows for 24/7 autonomous operation. An internet-connected onboard computer monitors the system’s performance, energy usage, and component health.