Antifouling Article
Antifouling Article
Antifouling Article
Antifouling 101
A Comprehensive Guide from Interlux
Antifouling 101
Jim Seidel
Assistant Marketing Manager
Contents
n Part 1
The Challenge
Weed Fouling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 03
Shell Fouling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 04
Slime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 05
n Part 3
n Part 2
How antifouling paint works
Hard Paints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 06
Ablative Paints
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 07
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 07
n Part 4
Non-Biocidal and Foul Release Coatings
Foul release coatings: The history
. . . . . . . . . . . . . . . . . . . . . . . 10
n Part 5
Common Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
n Part 6
Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
02
n Part 1
The choice and use of antifouling paints is one of the
most complicated questions a boater will need to answer.
At Interlux we help boat owners answer that question at boat
shows, online and at our technical service helpline. Many
boaters will just chose to let the boatyard decide put on
whatever you apply but make it blue, or they may ask their
fellow boaters what they are using or they may simply go to
the yacht chandlery and pick one that fits their price range.
Through our experience we have noticed that many myths and
misunderstandings have grown up around antifouling paints
and this is an attempt to demystify those misunderstandings.
The Challenge
One of the ironies of boating, whether Its for recreational or commercial
purposes is that the primary ingredient necessary for such activity
water is also potentially the biggest cause of problems. The
destructive effects of fouling marine growth have vexed man from the
beginning of his use of the worlds waters for relaxation and commerce.
Weed Fouling
Weed fouling is a by-product of the seaweed family that is familiar
to ail. True seaweeds are divided into three groups, by colors; Green,
Brown and Red. All are fouling growths and are found around the, globe,
and each has its own common characteristic. Like ordinary house or
garden plants, each of these seaweeds can only grow in the presence of
light. Green weeds need more light than brown which itself needs more
light than red and because of the need for light, weed fouling on boat
bottoms tends to concentrate itself near the waterline.
Weed growths (fouling) multiply and spread by means of tiny spores that
attach themselves to the bottom of the hull. Light is important to their
growth and reproduction, as explained above, but either too much or too
little light can be fatal to weed growths. The moderate amount of light
typically found at the waterline provides the ideal conditions for permits
them to thrive, particularly, when they are attached to the bottom of a
boat.
Enteromorpha:
A typical example of the green
weed that is found in coastal
areas throughout the world.
Ectocarpus:
The most common brown
colored fouling growth. It has a
branched structure Instead of
the filamentous structure of the
Enteromorpha and it also is
found at the lower portions of
the waterline.
Most people when they consider fouling think of shell fouling such as
barnacles or mussels but there are a host of other organisms such as
algae, slime, grass, bryozoans, Hydroids, diatoms, snails and worms that
would love to call the bottom of a boat home.
Fouling can be divided into two categories, weed (plant) and shell
(animal). The primary difference between weed and shell fouling are
their origins and appearance, but their destructive properties are equal
in potential.
Polysiphonia:
The red colored Polysiphonia, which has a branched structure with
feathered tips.
03
The owner of this boat waited a little too long to apply new antifouling!
These remarks have applied to the true seaweed, but as stated above,
there are various other fouling forms, that are classed as grass fouling,
but which are in fact animal fouling. The two most important of these
are hydroids, which are related to the sea-anemone, and polyzoa which
are related to marine worms. Both form soft branching growths, easily
mistaken for seaweeds. If they are placed in water and examined with a
lens, the branches are seen to be covered with what look to be minute
daisy-like flower heads, but which are little gelatinous polyps whose
tentacles move actively, expanding and contracting to capture their prey.
The color of hydroids and polyzoa varies from white and pink through
buffs and browns to red.
They are never green. The minute larvae, by which they are propagated,
are generally more repelled by sunlight at the time of settling than are
seaweed spores. This type of fouling consequently occurs more
abundantly on the lower parts of yachts.
Shell Fouling
Shell fouling is similar to seaweed growth in that the microscopic
organisms are hatched in the sea, swim, disperse and ultimately,
seek a resting place such as the bottom of a boat.
The most universally known shell fouling organism is the Acorn Barnacle
of which there are many species, ranging in size when fully grown from
0.75 cm or less, up to 4.0 - 7.0 cms in diameter. There are also Stalked
Barnacles or Goose Barnacles, the shell portion of which grows on a
long, flexible stalk.
When barnacles adhere to the bottom of a boat, they continually grow
and exert considerable pressure on the area where they are attached.
Fiberglass hulls are very hard and tough, yet they are not impervious to
the destructive nature of the barnacle. Left unattended or uncorrected
barnacles can do considerable damage to the gelcoat surface. When
scraped off they usually leave a ring of glue on the surface and
04
Tunicates or Sea-Squirts
Mussels
A form of animal fouling that grows flat to the surface are the
Bryozoans, which are made up of colonies of individuals, called Zooids.
Zooids are less than one thirty-second of an inch in size and live
together in an encrusting lacework crust, which is formed by a
limestone covering secreted by the colony. They feed on plankton and
bacteria by sweeping the surrounding water with cilia-covered tentacles
called lophophore. Bryozoan colonies can get very large stretching a
foot or more across.
Slime
Yachts frequently become coated with a slimy moss-like growth, usually
more noticeable on the sides than on the bottom. Such slimes are
vegetable, sometimes true seaweeds of a low order which forms a
tangled mass of microscopic threads, more often organisms called
diatoms. Different species of slimes vary in color; they are commonly
green, greenish-brown, brownish-red or black.
A typical slime film could consist of long filaments of the alga Ulothrix
together with Acthnahthes diatoms, attached by means of gelatinous
stalks bound up together with silt particles. Being stalked, some of these
diatoms manage to keep out of the toxic area around the antifouling
surface and so are not affected. Other slime forms have their own antiantifouling defenses, including in some cases the ability to chemically
bind normally toxic materials like copper into insoluble forms and
effectively inactivating them!
Slime fouling
Tube Worms
Barnacles
Bryozoa
Slime
05
n Part 2
How antifouling paint works
The best solution to the problem of fouling is treating the
hull with an antifouling paint. Antifouling paints contain
biocides that repel fouling organisms when released at a
controlled rate into the water adjacent to the hull.
The rate of release of biocides is important; if it is too fast, the
antifouling will fail prematurely, especially after a period of intense
activity, while if it is too slow, the antifouling will be ineffective,
particularly in areas with a high fouling challenge. It is at the settling
stage of fouling organisms that the adhesion and growth must be
prevented: once settled and firmly attached, growth is extremely rapid
and the organisms are beyond the influence of antifouling paints, and
can only be removed by scrubbing and scraping.
Choosing an antifouling with the correct biocide release rate does
depend on the severity of the problem locally. Other requirements vary
too. For instance, antifoulings with a high copper content cannot be
used on aluminum vessels without being specially primed first. Some
boats dry out for several hours on their moorings, at low tide, while
others are permanently immersed. Some boats need to be burnished
to a smooth, racing finish. Others require bright, attractive colors.
Thus antifouling compositions bear only a superficial resemblance to
other paints. Whether for protective or decorative use other coatings
are designed to be as permanent and as water-resistant as possible.
Antifoulings look like paints, smell like paints and are applied like paints,
but in order to function they require some water ingress in order to
release the biocides, in a continuous and controlled manner throughout
the lifetime of the composition. The antifouling film acts as a biocidal
reservoir which gradually becomes depleted. All antifoulings will
eventually fail when the concentration of biocide in the layer of water
adjacent to the surface falls below the critical level necessary to control
the larval fouling.
The dissolution process which allows removal of biocide is called
leaching and the rate of removal the leaching rate. The problem
in antifouling development is to produce products which will maintain
an adequate leaching rate of biocide for extended periods of time.
This must be combined with all the other necessary properties of
application, flow, leveling, drying, adhesion and film integrity necessary
in a film which is subjected to repeated immersion in sea water, and
subsequent drying out.
Failure of the biocide to leach adequately, or alternatively to be released
too rapidly, will lead to premature fouling. The thinner the antifouling the
less biocide reservoir it contains and too thin a film will lead to rapid
failure once all the biocide has gone. On the other hand, application
of five coats of antifouling will not give five times the lifetime except
in the case of copolymers. Other antifouling systems get clogged with
insoluble materials at the surface, before the biocide in the lower coats
can be utilized.
06
The effectiveness of the antifouling and its lifetime will depend on the
types and level of biocide(s) it contains, along with the types of resin,
natural or synthetic, used as binders. Very few biocides have found use
in antifouling compositions since very precise properties are required,
particularly in terms of toxicity and solubility in sea water. Many are too
soluble in sea water, while others are too toxic to be handled safely.
As you can see the delivery system of the biocide is a major determining
factor in how well the antifouling paint works and for how long it works.
In simple terms there are two methods of delivering biocide to the paint
film surface so that it can discourage growth, hard and ablative. These
terms refer to the way the resin interacts with the water.
Hard Paints
The technical term for these types of antifouling paints is contact
leaching. The paint dries to a porous film that is packed with biocides,
and these leach out as they come into contact with water. This leaching
is designed to release biocide throughout the season, but it is a diffusion
controlled process that starts at a high level and steadily decreases until
there is not enough biocide coming out of the paint film to maintain
fouling protection. Once the biocide is exhausted, the remaining hard
paint film remains intact.
Hard antifoulings do not retain their antifouling ability if kept out of
the water, and cannot be hauled and relaunched without repainting.
However one of the main benefits of this type of antifouling is its
resistance to abrasion and rubbing. This makes it ideal for fast
powerboats, racing sailboats or boats where the owners have the
bottoms scrubbed regularly. Most hard antifouling paints can be wet
sanded and burnished prior to launch in order to reduce drag and
improve hull speed.
The paint film of hard bottom paints continually builds up year after
year, and eventually becomes brittle, and starts to crack and flake off.
It is at this point that it will need to be removed.
Leached layer
~4 mils
Ablative Paints
Ablative types of antifouling are more efficient at delivering biocide
than Hard antifoulings and use less biocide to provide more antifouling
protection. To ablate means to wear away or erode, and there are
many antifouling paints that work by wearing away, but there are
several different ways that the paints wear away.
Self-Polishing Copolymers
SPC technology antifoulings work because the film contains an acrylic
copolymer that reacts with saltwater and this only occurs at the surface.
As a result, this chemical reaction controls and sustains the release of
biocides, not diffusion. Because this reaction is chemical rather than
physical it takes place at the same rate whether the boat is underway
or sitting at the dock, throughout the lifetime of the antifouling, without
decline. This technology is what made the tin-based (TBT) copolymer
coatings last as long as they did, but since the demise of tin-based
coatings the only coating in the yacht marketplace that uses an acrylic
SPC copolymer is Micron 66.
Why does the biocide release remain constant
for SPC antifoulings?
n
The chemical reaction between SPC copolymer & salt water occurs
at surface only
Chemical reaction
at surface only
Leached layer
~4 mils
Biocide
07
n Part 3
Substrate
Paint
Leached layer
3 mils
Substrate
Paint
Leached layer
<1 mil
Biocides
Significant work has been carried out to determine the optimum levels
of biocides required in our antifouling paints in order to achieve the
industry-leading performance that our customers expect. This work
ensures that formulations are properly engineered, rather than over
engineered, and that the environmental impact is minimized. At the
same time, Interlux is actively funding work developing efficient new
biocide delivery systems to ensure that the right amount of biocide is
released into the environment when it is needed. Together, these two
activities will ensure that we continue to offer our customers the most
effective antifoulings with the least environmental impact.
Cuprous oxide and metallic coppers have been in common use for
100 years or more and they still are the basic biocides used in many
antifouling paint formulations. Cuprous oxide works in an antifouling
paint by discouraging the attachment of the larval forms of shell fouling
such as barnacles and mussels. It is also an excellent antimicrobial and
will work against slime and grass growth but requires a much higher
release rate to control this type of fouling. The best antifoulings also
contain a boosting biocide combined with the cuprous oxide to help
control weed fouling. Cuprous oxide is available in many colors ranging
from dark red to dark purple. This limits the color selection of antifouling
paints to the darkest shades.
Cuprous Oxide
08
PERCENT
38.62%
2.00%
59.38%
100.00%
09
n Part 4
In terms of a material being environmentally friendly it needs to be
considered as a whole process, i.e. examine all of the aspects of the
material, how it is obtained, how it is used and what happens to the
material when it is released into the environment. As part of this, the
methods used to extract the natural products from their source need to
be considered. The most common source of natural products are plants;
leaves, bark, flowers are all used.
The process to extract material from a plant is usually two or three
steps; often involving mechanical crushing (for example olives are
crushed in order to obtain the oil), distillation (usually steam distillation)
and purification. Each step uses energy and generates by-products that
require disposal. Extracting materials uses resources in the same
manner as do pure synthetic manufacturing techniques. Quite often
the final stage of extraction of natural products is a further synthetic
step in order to modify the product slightly in order to give the desired
properties.
In the case of fouling deterrence, the term natural is often used to
imply that the ingredient will not require any formal registration to allow
its use as an active ingredient in a formulation. This is not the case as
any ingredient in any formulation (whether antifouling paint for boats,
anti-fungal paints for masonry or wood preservatives) that exhibits an
activity towards a fouling species must be registered as a biocide under
many countries regulations (e.g., the Environmental Protection Agency
in the USA and the Biocidal Products Directive in the EU member states).
Approval through these legislative systems involves assessments of
human and environmental exposure risks. Compounds that exhibit rapid
degradation to non-active species in the environment are more
favorably considered than those that do not.
Yacht paint companies routinely test compounds for antifouling
properties, both compounds derived from natural sources and synthetic
compounds. Combining them with technical expertise on delivery
mechanisms, yacht paint companies aim to develop and test materials
that have good antifouling efficacy at low levels and which degrade
rapidly in the environment so that they do not persist and cause longterm environmental issues.
It is the combination of properties of a material that makes it
worthwhile developing an antifouling product from it. Firstly it needs
to be efficacious and deter the settlement of fouling organisms and
secondly, it must degrade rapidly into non-active materials so that it does
not persist in the environment. Unfortunately, neither of these properties
is guaranteed just because a material is from a natural source.
If you are interested to read more about our environmental ratings
and performance, please visit www.echoprogram.com
10
Non-Biocidal Coatings
The control of surface roughness and of fouling is essential
to keep hulls as smooth as possible, and to help minimize
drag. Controlling fouling using an antifouling paint
containing biocides is the most common way of keeping
hulls as efficient as possible, but there are coatings that
can do this without the use of biocides and here at Interlux
we refer to these paints as Foul Release coatings, with the
brand name Intersleek.
Foul Release coatings do not contain active biocides and
cannot actively repel the attachment of fouling organisms.
The purpose is to create a surface which proves to be
extremely difficult for growth to attach. Once fouling has
begun, the adhesion is weak and the sooner that it can be
removed the easier it will be to remove. These coatings will
work best on boats that are used regularly or are cleaned by
a diver on a regular basis.
Intersleek 900 has been formulated to make it very difficult for fouling
organisms to adhere to the coated surface. The surface energy has been
engineered in such a way that a very unattractive surface is presented
to the fouling organism.
Hydrophobic:
Water on Silicone
Amphiphilic:
Water on Intersleek 900
There are other coating that are used on the bottoms of boats that do
not contain biocides but are not designed to be Foul Release coatings
such as the Intersleek. One such coating is VC Performance Epoxy.
VC Performance Epoxy is an extremely hard two-component epoxy
that contains a flouro microadditive.
11
n Part 5
When using a roller the tendency is to push too hard on the surface
of edges like this so these areas should be done with a brush rather
than a roller.
12
Fouling:
Strut was not properly primed and electrolysis developed between the
bronze in the strut and the copper in the antifouling paint.
Burnback:
This is caused by improperly priming the underwater metal. The copper
biocide is eroded away due to electrolysis and no antifouling protection
is left. This will continue on the fiberglass in concentric circles away from
the metal. While this most commonly happens with paints that have an
acrylic resin it can happen with any antifouling paint.
Detachment:
The time window was missed between the no-sand primer and the
antifouling paint.
Detachment:
Improperly prepared surface resulting in excessive paint build-up, and
a very rough surface.
13
n Part 6
Glossary of terms/technology explained
A
Ablative
Polishing
Hybrid SPC
14
L
Leached Layer
A biocide depleted spent layer at the
surface of the coating. In SPC antifoulings
the leached layer is always thin, <15m
(0.6 mils), providing a smooth surface,
conversely, CDP leached layers can become
very thick, >75m (3 mils), resulting in
increased surface roughness plus removal
and overcoating difficulties.
Leaching Rate
The release of biocide per unit time.
There are three technologies or delivery
mechanisms available to control biocide
release SPC, CDP and a combination of
the two, known as Hybrid SPC.
Polishing Rate
Film thickness reduction per unit time.
For SPC antifoulings, polishing rate is
directly proportional to vessel speed.
R
Rosin
Naturally occurring resin extracted from
trees. Rosin is soluble in seawater.
S
Self Polishing
The paint polymer or binder system is
soluble in sea water. Solubility can be
achieved either by a chemical reaction e.g.
Hydrolysis, as in SPC technology or by the
use of Rosin e.g. in CDP technology.
Hard Antifoulings
Antifoulings with low Rosin content are referred to as Hard or Contact
Leaching antifoulings and do not polish.
Hard paints may be multi-seasonal as they can last for long periods
of time in the water but they cannot be hauled for long periods of time
and relaunched without repainting.
Boats that have been painted and are past the maximum time before
launch on the label but no more than 12 months past their launch
date scuff sand with 220 grit sandpaper or a maroon Scotch-Brite
pad prior to launch.
Boats that have been launched but are in the water for less than
24 hours lightly pressure wash to remove surface contamination
(salt and dirt etc.). Follow label instructions for maximum launch time
from date of painting.
Boats that have been in the water for more than 24 hours but
less than 30 days pressure wash immediately after hauling.
No additional work is needed if the boat is relaunched with 72 hours.
If the boat will be out of the water for more than 72 hours will need to
be sanded with 220 grit sandpaper immediately prior to relaunching.
Boats that have been in the water for more than 30 days pressure
wash when hauled, sand with 80 or 100 grit sandpaper and recoat.
Recoating is necessary even if the boat will be out of the water for
less than 72 hours.
Ultra
Trilux 33
VC Offshore
Fiberglass
Bottomkote
Fiberglass
Bottomkote
Aqua
15
, Interlux, the AkzoNobel logo and all product names mentioned in this publication are trademarks of, or licensed to, AkzoNobel. Akzo Nobel N.V. 2012.