result marks a major milestone for an
organisation that has run through years of
numerical analysis, model prototyping and
simulation in the quest to pick up plastic.
Slat’s initial designs were static,
involving stringing V-shaped collectors
anchored to the sea bed at particular
ocean gyres. The idea was that plastics
borne on ocean currents would drift into
the oating net – like draining pasta into
a colander. However, in 2017 that idea
changed to mobile collectors. Partly, that
was because of the massive cost involved
in building anchors in water 4-5km deep,
according to technical manager Arjen
Tjallema.
There was another reason too. Gyres
are circular currents. “But when we dug
more deeply into that data, that circular
current is an average over time. But in
day-to-day conditions, the current is going
in different directions as well. So if we
have a large V-shaped stationary system,
on average the current is owing into it,
but at some times it is also owing back
out, which means that plastics also are
owing into it, and back
out, and maybe
back in,
or they pass it, or whatever. On the other
hand, if you have a moving system that
can orient with those changing conditions,
you could have a system where plastics
are owing in, but not back out again.
That’s much more ef cient,” he contends.
About that stuff, then; and it might not
be quite what you think. Some debris that
oats because of air trapped inside, such
as Styrofoam, is so light it tends to get
blown to shore. More common at sea are
plastics that oat because they are less
dense than seawater (about 1,030kg/m).
Battered by waves, large bits of oating
plastic tend to break up into microplastics
that enter the food chain. Even exposed
in sea and sun, they can persist for
hundreds of years before decomposing
chemically.
Two collection projects in the Paci c
– rst, a otilla of sailboats; second,
an aerial survey – helped the group
understand exactly what kinds
of materials end up in the
middle of the ocean. The most
common types found were
polyethylene and polyester,
but relatively little lm-based
plastic. They also found a signi cant
quantity of large objects, such as
discarded shing nets. Items larger than
half a metre made up 45% of the mass of
discarded plastic.
At rst glance, the current system
resembles a temporary oil spill boom,
which is a long,
thin tube in ated
with air that
suspends a
at
curtain of material a few feet beneath
the surface. Both collect and contain
oating debris. And in fact the company’s
rst prototype testing, in the North Sea,
ENVIRONMENT
The solution for marinas
Another kind of automated collector of oating
rubbish, but on an entirely different scale, is
the Seabin, devised by Australian boatbuilders
Andrew Turton and Pete Ceglinski, who has a
background in product design. It is now being
used around the world.
The size and shape of an ordinary domestic
bin, the Seabin V5 device attaches to oating
pontoons, pumps water through a plastic mesh
sieve, creating a current that collects litter and oil
on the surface of water in locations like marinas
and docks. It is mounted in calm water (currents
less than four knots), and its inner sleeve oats
with the tide. The company says it can pull waste
from up to 50m away in dead calm conditions.
The company recommends that the 500mmdiameter
bin, which has a capacity of 20kg, be
checked twice a day. Its sieve can capture pieces
as small as 2mm, and estimated daily litter
catch is 1.5kg. The mounting bracket
includes a sacri cial anode to prevent
rusting.
Ceglinski set up a manufacturing
site in Palma Mallorca, Spain
in 2014; he and Turton set up the
Australian company in 2015. In 2016,
the project caught the imagination of the
internet, and raised $267,000 in crowdfunding.
Construction rm Poralu Marine signed up as
worldwide manufacturer and distributor. The rst
unit was installed in the marina of La Grande-
Motte, France.
UK installations, with sponsor (if known)
Banff Harbour, Aberdeenshire (Aberdeen
Council/KIMO UK)
Bangor, County Down (Ards and North Down
County Council)
Brough, Yorkshire (Wartsila)
Cowes, Isle of Wight: UKSA Marina
Ipswich, Suffolk: Debbage Yachting
London’s Royal Victoria Dock (Butter eld Group)
Poole, Dorset: Land Rover BAR (Ben Ainslie
Racing) pontoon
Port Solent, Portsmouth, Hampshire (two):
Premier Marina
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