International Paints’ foul release coating Intersleek 700 has shown good results in a survey conducted on LNG ships, the company reported.

More than 60 full ship applications of Intersleek 700 had been carried out on deep-sea ships including 11 LNG vessels. Of these LNG vessels, four re-docked with only light slime fouling in each case and no macro-fouling, giving a Dataplan Fouling Rating of 0, the company reported through its inhouse journal Propeller.
All the vessels were inspected over periods ranging from 25 months to 36 months after application.
One of the vessels Al Khor was drydocked in Dubai 30 months after application of Intersleek 700. According to International Paints, after low-pressure fresh water washing commenced on the vertical slides, two areas could be seen where the light slime fouling had been washed off revealing the original Intersleek 700 glossy surface. The vessel was ready for the next in-service period without any further work necessary.
One of the keys to efficient movement of vessels is fouling control. Loss of speed primarily occurs due to fouling, either on the main hull or on the propeller or on both. Macro-fouling (weed or animal) can reduce speeds by more than 1 knot or increase fuel consumption by more than 10 per cent as a result of the extra drag caused by the fouling. Increased fuel consumption leads to increased greenhouse gas emissions.
Analysis on a range of vessels has shown that LNG ships suffer the greatest fouling challenge. The reasons for this are not clear but it has been speculated that the use of the ‘dump’ condenser by steam turbine ships when in port may produce higher seawater temperatures around the hull when stationary, resulting in more prolific fouling growth.
The most commonly used antifoulings are the high-performance Self Polishing Copolymer (SPC) types, which are based on synthetic acrylic polymers that undergo a chemical reaction with seawater at the surface. This results in a slow and steady dissolution (polishing) of the paint thus providing controlled release of the biocides contained in the paint formulation for up to 60 months in-service life. In addition, water flow over the hull results in a smoothing process whereby peaks of roughness are polished away preferentially, thus minimising drag and maximising fuel efficiency.
Until 2003, SPC antifoulings were predominantly based on tributyltin (TBT) acrylic polymers. Since 2003, as a result of the IMO International Convention on the Control of Harmful Antifouling Systems on Ships, TBT anti-fouling systems have been phased out. They have been mainly replaced by acrylic systems based on either copper acrylate, zinc acrylate or silyl acrylate copolymers.
Foul release technology was first discovered in the early 1970s but it is only in recent years that commercial products based on the technology have been used on deep-sea vessels.  Most commercially available foul release coatings use a PDMS (polydimethylsiloxane) cross-linked polymer as the main film-forming material. This gives a very smooth, lower energy surface, which is elastomeric (rubbery) in nature. Studies have show that it is a combination of both low surface energy and elastic modulus that imparts the fouling release properties. International Paints listed several advantages from the environmental and operational standpoints in the use of foul release coatings on LNG ships compared to biocidal antifoulings.
It said they were more durable; there was no change in colour over time; paint usage was reduced; M&R costs at future drydockings were lower; there was evidence of higher volume solids and lower solvent content, and no biocides were released into the sea.
With regard to lower M&R costs at future drydockings, it was pointed out that the coatings were quick to wash down, the wash water was not treated as toxic waste and only one coat re-coat was required after 60 months in service. The draft marks did not generally need repainting and the drydock time was shorter.
“The environmental benefits can form an integral part of an overall environmental management plan and the operational benefits can result in significant savings at future maintenance and repair dockings,” said International Paints
On propeller coatings, International Paints said the use of biocidal antifouling coatings on propellers was generally not found to be successful since they did not last long enough under the high shear conditions.
“By contrast,  foul release coatings work best under shear conditions, with the first successful trial on a propeller being reported in 1993, it said.
“Since then the foul release coating Intersleek has been applied to the propellers of over 80 large ships including carriers.” 
Studies were recently carried out at Newcastle University to examine the effect on ship performance of coating a propeller with Intersleek.
“Speed trials using the university’s research vessel Bernicia showed that coating the propeller with Intersleek did not in itself give any performance enhancement compared to the uncoated clean and smooth condition (Rubert Scale A). However, the trial did show that the propeller was kept totally free of all macro-fouling throughout the year, where previously it had become extensively covered in tubeworms and barnacles,” said International in the Propeller article.
“The ability to prevent fouling on propellers has been substantiated from our experience on the Deep Sea ship applications carried out,” said International Paints.
“Typically around the edges of the blades where cavitation occurs, the complete coating system is removed down to the underlying bronze surface. This effect is generally worse on the suction (forward) side but fouling cannot grow in the extreme operating conditions in these areas. On the remainder of the propeller where the coating system is not removed, the Intersleek remains fully intact and without any fouling.
“Thus the propulsive efficiency of the propeller is maintained and there is no requirement for in-water cleaning throughout the in-service period.”
Describing the use of foul release coatings on underwater hulls and propellers of LNG ships as “a revolutionary new way to improve efficiency, International Paints said they not only provided improved environmental control, since they did not use biocides to prevent fouling, but they also had been proved to provide better fouling control than SPC antifoulings.
“This results in increased fuel efficiency and reduced maintenance costs,” it said.