proportions would need to match the
nal oater length). Floaters prevent the
parachute from sinking too deep, where
submerged currents might pull the net
away from the surface currents carrying
oating plastic. To prevent the stress
concentration problem on the oater, the
screen was hung from a second, brandnew
structure: a cable suspended from
a chain of cork oaters. The two arcs are
attached by cords at either end.
This worked better; and an issue
of rubbish overtopping the screen
encountered with this design was xed by
installing larger cork oats.
Although it is clear that future test
systems will be larger than the current
50m model, there is no particular vision
about how big they will get: “Scale in itself
is not so much of a goal for us. It is about
the ef ciency of doing a complete cleanup
operation. How big a system should
become depends on the design of the
The next project
Under development by The Ocean Cleanup
system, because it may well determine
how fast it can collect plastics, and how
much plastic it can contain,” according to
Tjallema – who adds that the organisation
is currently leaning towards fewer, bigger
systems rather than a greater number of
small ones. That will minimise the number
of costly trips required for a vessel to carry
away the rubbish, currently estimated to
be needed from weeks to months. The
nets are currently emptied by hand; better
ways to do that will be investigated once
the system is fully-functional, the company
says.
Tjallema concludes: “What we are
trying to achieve is to minimise the cost
it takes for a certain amount of plastic to
be removed from that area.”
since 2015, the Interceptor barge complements the organisation’s
founding mission by attacking the ow of plastic garbage at its source: rivers.
“To truly rid the oceans of plastic, we need to both clean up the legacy and close the tap,
preventing more plastic from reaching the oceans in the rst place. Combining our ocean cleanup
technology with the Interceptor, the solutions now exist to address both sides of the equation,”
says founder Boyan Slat (pictured above).
The Ocean Cleanup Interceptor is powered by roof-mounted solar panels, charging onboard
lithium-ion batteries. The barge is anchored to the riverbed to utilize the natural ow of the river
to catch the plastic on a submerged end of a conveyor mounted between pontoons. The conveyor
delivers the waste on to a shuttle that feeds six dumpsters. Total storage capacity is 50m³. It is
intended to operate continuously and without the need for technicians. An internet-connected
onboard computer monitors the system’s performance, energy usage, and component health.
According to the company, this vessel is capable of extracting 50,000 kg of trash per day – even
reaching 100,000 kg per day under optimised conditions.
The Interceptor is moored at one end of a oating barrier used to direct the garbage into the
system. The barrier only spans part of the river so as not to interfere with other vessels and does
not harm the safety, nor impede the movement of wildlife. When the interceptor is almost full, it
automatically sends a text message to the local operators to come
and collect the waste. Operators then remove the barge, bring it
to the side of the river, empty the dumpsters, send off the debris
to local waste management facilities, and return the barge back
into the Interceptor.
Four such ships have been built as of late 2019. Two
another plastic welded joint along the
entire length of lower edge of the oater.
The 3m-deep submerged screen,
weighted to keep it vertical, was of a
woven nylon mesh whose pore size
ranges from 3-10mm. The screen needs
to be permeable to water so that small
currents don’t tend to wash underneath
it, as they might carry particles of plastic
out of the net with them.
As the oater bobs in the waves,
it bends. The weld seam tended to
concentrate stresses at that point in
the oater wall, until a piece broke off.
Although that effect was predicted, it
turned out to be a much bigger factor than
anticipated, reducing the fatigue life of
the system. Future trials will explore this
very point; Tjallema says the system’s
potential lifetime remains uncertain, but a
decade at least is the goal.
In the meantime, the latest design
was tweaked to x each of the issues.
To better control the system’s speed and
direction, it was made smaller – 50m
wide. A limitation on the lower end of
size relates to its behaviour in the water;
the oater beam needs to be longer than
a couple of wavelengths to avoid the
‘strange’ loading effects that might occur
at around a wave length, according to the
technical manager.
And during the latest test, the
researchers tried out six different ways of
controlling the net’s speed. Most effective
was a 20m-diameter parachute, attached
by a 200m-long cable (although those
systems are already operational in Jakarta (Indonesia) and
Klang (Malaysia). Other systems are planned for Vietnam, the
Dominican Republic and Bangkok, Thailand.
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