Home' Ships and Shipping : December 2009 Contents The guidelines are anticipated to lead to the increased
frequency and duration of dry-docking and/or in-water cleaning as
more time will probably be required to clean niche areas and
different coatings may be required on different parts of a vessel.
Care will need to be taken to ensure that the position of docking
blocks and supports does not leave unprotected spots on the hull.
According to Dr Rob Hilliard, managing consultant for
InterMarine Consulting of Australia, a hull clean for ships
operating between 15 and 23 knots primarily aims to reduce drag.
It focuses on algal beards along the waterline and the hard fouling
that projects from the plating of shaded hull undersides.
Cleaning for bio-fouling involves checking areas such as behind
anode blocks, inside stud recesses, behind rope guard plates, on
and around rudder posts and rudder-tab slots, strop holes and eyes,
mouths of apertures, and inside hull openings such as thruster
tunnels. Attention should also be directed at the internal seawater
circuits including sea chests, sea strainers, strainer boxes, coffer
pipes, manifolds and fire fighting pump apertures.
There is a concern within industry that a heightened awareness
of the issues resulting from the publishing of the guidelines might
lead coastal states to take unilateral actions to prohibit cleaning
activities in their waters. This has been the case with the IMO
ballast water convention which aims to stop the spread of invasive
species carried in the ballast tanks of merchant vessels.
Modification to existing hull-cleaning facilities and practices
may be required to ensure residues are not released to the marine
environment. New technologies are required to achieve this
in-water and Dr Grant Hopkins, senior scientist with the Cawthron
Institute in New Zealand, is developing a two-diver-operated
rotating brush system coupled with suction and collection
capabilities. So far, whilst the machine is well over 80 percent
successful, diver error, persistent fouling and inaccessible niche
areas pose significant challenges.
Tim Wilkins, regional manager for Asia-Pacific at Intertanko
and secretary to the organisation's environment committee, has
been involved in the development of the new guidelines and he
believes that Intertanko members undertake regular hull
maintenance, typically every three to six months. This brings
measurable improvements in fuel efficiency, but there are concerns
amongst owners regarding changes resulting from a concern for
invasive species. "In the draft guidelines there is a distinction
between micro and macro fouling and that's what we put in there
because we felt that micro-fouling, which is the slime layer, wasn't
necessarily high risk and, in fact, it is very difficult to maintain.
You would have to get a diver down to clean your hull every three
to five weeks if you wanted to keep the slime layer off. We feel the
focus of coastal states should be on the high risk in terms of
invasive species, and that is the hard or macro-fouling."
Even minimal fouling may be enough to enable a range of
organisms to colonise a hull, says Dr Richard Piola, a marine
scientist with the Cawthron Institute. "It doesn't have to be
something big. Even thin slime or algal layers might be enough
to disrupt or inhibit the effective release of biocides from
Copper-based anti-fouling is generally considered to be less
effective than the now banned TBT-based paints and Dr Piola says
that several groups of organisms have shown a significant
tolerance for copper. These groups have also been associated with
invasive species introductions from hull fouling. Their tolerance
for the high levels of copper found in areas such as ports may
further assist in their establishment once transported.
While silicone-based fouling release coatings may not contain such
biocides, they still carry the potential for introducing species if used
incorrectly, says Dr Piola. Some research has shown that removal of up
to 90 percent of attaching organisms is directly dependent on the
speed of the vessel, meaning that some fouling release coatings require
speeds of over 20 knots to be completely effective.
Once the guidelines are introduced next year, there may be a call
to make them mandatory via an IMO convention. These conventions
typically relate to commercial vessels 400 gross tonnes and over.
In the longer term, vessel design modifications may be
introduced to simplify hull surfaces for the improved application
of coatings and the ease of subsequent cleaning. "I would see the
effect on hull form being more influenced by the almost
inevitable GHG indexing of ships than the bio-fouling," says
Captain Graham Greensmith, lead specialist, external affairs, for
classification society Lloyd's Register. "But there is a link, of
course, as a clean hull means a more efficient ship and therefore
less GHG emissions."
Given the recent slow-down in new building orders there may
be little incentive for incorporating bio-fouling initiatives into
vessel design at present. A more immediate concern is the potential
bio-fouling risk of laid up vessels. When the record number of
vessels and barges currently idling around Singapore and Malaysia
start to move again, fouling may need to be considered from both
a fuel efficiency and a bio-fouling perspective.
December 2009 SHIPS AND SHIPPING
Jet washing for bio-fouling
Another fouling niche -- small apertures
Part of a wide range of fouling species
Manual cleaning in small gaps
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