span of marine-based biofouling organisms. Conversely, fouling release systems are generally biocide-free. They are based on
polydimethylsiloxane, known as PDMS or silicone, that minimizes the strength of adhesion of the fouling organism, allowing for release during the operation of the vessel. The problem
here is that PDMS coatings have limited effect at low operating speeds. This is particularly relevant in today’s market where
ships can be idle for longer periods or are steaming more slowly
to save on fuel costs.
Resistance to Fouling
The way around this is to combine a PDMS coating with a
hydrogel to deliver improved resistance at slower speeds or
when the vessel is idle. A hydrogel is a layer of water trapped
in or around a network of hydrophilic polymers. An organism
wanting to attach to a hydrogel-covered hull will first need to
recognize if the surface is suitable for settlement. As the hull is
covered in bound water, most organisms will simply not recognize it as a suitable surface and find a home elsewhere. A water
bound surface will also require the organism to expel the water
before it can apply its own adhesive direct to the hull, and most
organisms don’t have the energy to do this.
Actiguard Technology
Moving the concept on, we are now combining the hydrogel
layer with biocide to form a biocide-activated hydrogel layer
– a technology called Actiguard®. Here, the hydrogel traps the
biocide during its diffusion out of the film and this increases the
surface concentration of biocide. It thereby prolongs the reten-
tion of biocide on the surface enabling Actiguard to remain ex-
tremely effective with lower amounts of biocide. Because of this,
an Actiguard coating is able to release biocide in a stable and
controlled manner for vessel speeds
(or currents) exceeding 0.1 knot
and upwards. This is significant for
a ship owner as it means the hull re-
mains protected even when the ves-
sel is idle, or is slow steaming. From
an environmental perspective, the
stable release of biocide irrespective
of speed means that less biocide is
released into the oceans when trav-
elling at higher speeds.
The efficient use of biocides allows for a very low pigment and
filler volume concentration; they
also enjoy a low VOC content.
Low biocide content also ensures
the coating is smooth after application, which is important for a vessel
to maximize its fuel efficiency and,
therefore, reduce operating costs.
Even if the hull suffers scratching, Actiguard offers a window of
defense and tests have shown that
Actiguard coatings will retain their protection levels for at least
22 months when scratched.
Performance Consistency
Efficiency is paramount in the current shipping markets and
tests of Actiguard technology show that its fouling defense properties remain effective for vessels that switch from slow to fast
steaming and that remain idle for periods up to 120 days. This
is particularly interesting for larger container vessels and tankers that, for example, may wish to increase speed on one route
to meet schedules and slow steam on the other to achieve extra
fuel savings. It also means an operator can lay up a vessel for up
to four months without having to clean the hull. Additionally,
fuel savings of 6 percent on average, across the entire docking
interval, have been achieved which is significantly higher than
conventional self-polishing technologies. Further efficiencies are
gained due to the extended re-coating interval which reduces the
time a vessel spends in dry-dock.
Galvanizing Change
Tough markets and challenging physical conditions are encouraging those who operate in such environments to demand more
from their coatings provider. This provides an opportunity to
push harder and develop ever more sophisticated coatings solutions for the benefit of our customers, and the environments
in which they operate. Contemporary coatings must offer the
highest levels of protection as well as opportunities to enhance
efficiencies and control costs. In turn, as coatings providers, we
can play a significant role in helping our customers develop their
operational capabilities. A heavy investment in continued R&D
will pay dividends in both quarters, and we will all benefit from
the ripples of change. CW
