AFS Convention
Learning objectives: After reading this you will be able to understand and describe
AFS convention.
Introduction : This section provides details as below:
1. Basics of convention on anti fouling systems.
International Convention on the Control of Harmful Anti-fouling Systems on Ships
- AFS 2001
Adoption: 5 October 2001; Entry into force: 17 September 2008
The Convention prohibits the use of harmful organotin in anti-fouling paints used on ships
and establishes a mechanism to prevent the potential future use of other harmful
substances in anti-fouling systems. Anti-fouling paints are used to coat the
bottoms of ships to prevent sea life such as algae and mollusca attaching
themselves to the hull – thereby slowing down the ship and increasing fuel
consumption.
In the early days of sailing ships, lime and later arsenic were used to coat ships' hulls, until
the modern chemicals industry developed effective anti-fouling paints using metallic
compounds. These compounds slowly "leach" into the sea water, killing barnacles and other
marine life that have attached to the ship. But studies have shown that these compounds
persist in the water, killing sea-life, harming the environment and possibly entering the food
chain. One of the most effective anti-fouling paints, developed in the 1960s, contains the
organotin tributyltin (TBT), which has been proven to cause deformations in oysters and sex
changes in whelks.
Under the terms of the AFS Convention, Parties to the Convention are required to prohibit
and/or restrict the use of harmful anti-fouling systems on ships flying their flag. Anti-fouling
systems to be prohibited or controlled are listed in an annex to the Convention, which will be
updated as and when necessary. The Convention provides for the establishment of
a “technical group” to include people with relevant expertise to review
proposals for other substances used in anti-fouling systems to be prohibited
or restricted. Article 6 on the process for proposing amendments to controls
on anti-fouling systems sets out how the evaluation of an anti-fouling system
should be carried out.
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Let us discuss the following, with Reference to various alternatives to tin-based antifouling
paints,
a) Hull roughness of different types of antifouling paints.
b) Enhancement of foul release coatings by oil incorporation.
c) Personnel and health safety during application of antifouling paints.
Anti-fouling paints are used to coat the bottoms of ships to prevent sea life
such as algae and molluscs attaching themselves to the hull – thereby
slowing down the ship and increasing fuel consumption as well as
accelerated rusting of the ship’s hull.
The Harmful Anti-Fouling Substances on Ships Convention prohibits the use of harmful
organotin in anti-fouling paints used on ships and establishes a mechanism to prevent the
potential future use of other harmful substances in anti-fouling systems.
Since the banning of TBT (Tributyltin) based on IMO’s “The International Convention on the
Control of Harmful Antifouling Substances on Ships, 2001", most antifouling coatings now
are Tin free.
a) Hull roughness and types of antifouling paints:
Hull roughness is defined as maximum peel off true height, expressed in
microns. Roughness in a foul-release coating will reduce its ability to
discourage adhesion and slime/micro fouling can take hold. Mechanical
damage from example from tugs is especially critical for these types of
coatings requiring special care in operations as the damaged parts has no
fouling protection.
There are three main categories of tin-free antifouling paints (TBT free)
1.Controlled Depletion Polymer (CDP) paint
A traditional antifouling type based on water-soluble natural or synthetic pine
rosin mixed with a biocide. An insoluble reinforcing polymer resin is added to
create a skeleton to give the rosin better mechanical properties. The
controlled dissolution of the rosin matrix releases the biocides.
CDP is based on copper.
It also contains some very strong boosting biocides.
The biocides are released by diffusion; the dissolution gradually slows down due to a
leached layer formed by insoluble materials at the surface.
The roughness of the surface and fuel consumption will, therefore, increase as time
passes.
The average hull roughness (AHR) increase of these coatings is estimated at 40
microns/year
2.Hybrid TBT free paint
Hybrid is an antifouling which has the CDP features of surface
tolerance and attractive volume solids, control of biocide release and
reduced leached layer size.
Since CDP and Hybrid antifouling are not designed for more than 36 months in-
service on the vertical sides of a vessel, the power/fuel penalty for these products
rise sharply after three years
For Hybrid TBT Free antifouling, offers a balance of CDP type and SPC type antifouling
properties with performance and AHR increase assumed to be midway between the
two at 30 microns per year
3.Self-Polishing Copolymer (SPC) paint
An insoluble metallic or organic synthetic polymer (e.g. copper-acrylate or
silyl-acrylate) that contains a biocide. Through a chemical reaction –
hydrolysis – the polymer becomes soluble. Its subsequent dissolution
releases the biocide. The chemical reaction provides good control of the
dissolution rate and results in a much thinner leached layer and smoother
surface profile than possible with CDPs. No ship movement is required as
there is no residual 'skeleton,' and the surface is self-smoothing. Five years
of service for high-quality systems can be achieved. The average hull
roughness increase is estimated at 20 µm per year
SPC contains smaller amounts of biocides than CDP and is also less
toxic.
The base is copper as in CDP, but the amount needed is only two-thirds to that of
CDP.
The other biocide used in SPC is zinc pyrithione. The function is based on a chemical
reaction with water (hydrolysis).
SPC has a more controlled leakage of biocides over time which reduces the risk of
fouling.
For Self-Polishing Copolymer (SPC) antifouling, the average increase was found to be
significantly less, at 20 microns increase in AHR per year
4.Fouling Release paint
A biocide-free coating that uses non-stick properties to control fouling. It is
usually silicone or fluoro-silicone based and designed to shed micro or macro
growth when the vessel is underway. For slower vessels (less than 15 knots),
this is a challenge for even the best coatings, so some 'soft' cleaning is
usually required to remove the micro fouling. If the vessel is stationary for
some time, barnacles and other macro-size biotas can become attached.
Achieving a full release of all fouling through ship speed impact has proven
to be a challenge in some cases. The coating gains some of its effectiveness
from its extremely smooth surface, which must be maintained for best
performance.
Fouling release is an antifouling paint, which is free from biocides.
It usually is silicone-based and leaves a non-stick surface.
The efficacy is dependent on the speed of the vessel as any attached fouling is
supposed to wash off.
For Foul Release antifouling, the AHR increase is assumed to be only 5 microns per
year
b) Enhancement of foul release Coating by oil incorporation:
1. Foul release coating have been developed as an alternative to biocide
containing Paints. Its functions by minimizing the adhesion strength of
attached organism, which are removed as the vessel moves through
the water.
2. The method for the enhancement of fouling release performance has been oil
incorporation, in which a polydimethylsiloxane (PDMS) oil is incorporated into a
silicon matrix.
3. Oil by their nature are lubricants and therefore should also decrease the coefficient of
friction of hull surface.
4. Due to the additional of oil to the solution for the decrease the adhesion barnacles
and certain species of oyster.
5. They not only provide improve environmental control, since they do not use biocides
to prevent fouling, but they have also been proven to provide better fouling control
then SPC antifouling.
c) Personal and health safety during application of antifouling paints:
1. When applying this paint before the person should wear the full PPE
such as goggles full body coveralls, covered shoes and chemical
resistance gloves.
2. Respiratory protective equipment should be worn where the paint applied in area of
poor ventilation.
3. spray painting and antifouling maintenance should be done in calm weather. this
reduce the chance of your activity impacting other people or
will
environment.
4. Supervisory staff should ensure that everyone except the trained painters should be
completely excluded from the spraying area.
5. Cleaning of foul-release coatings should only be done with a light touch and soft
pads. In all cases, the advice of the paint manufacturer should be followed.
6. IMO’s MEPC.207(62) resolution on "Guidelines for the Control and Management of
Ships' Biofouling to Minimize the Transfer of Invasive Aquatic Species” should be
followed. It asks for a Bio-fouling Management Plan and a Bio-fouling Record Book to
be on-board.
Table - Anti-Fouling Systems:
Effective from 1 Anti-Fouling Adopted by MEPC 76:
January 2023 Systems
Amendments to the IMO Convention for the
Control of Harmful Anti-fouling Systems on
Ships (AFS Convention), to include controls
on the biocide cybutryne. Ships shall not
apply or re-apply anti-fouling systems
containing this substance from 1 January
2023. Ships shall remove or apply a coating
to AFS with this substance at the next
scheduled renewal of the anti-fouling
system after 1 January 2023, but no later
than 60 months following the last
application to the ship of an anti-fouling
system containing cybutryne.
