Back to the future

Back to the future

When Alex Milne and Sandy Christie discovered in the 1970s that tributyltin (TBT) copolymer coatings were remarkably effective at polishing predictably over time, they could have had little clue that their findings would provide a basis for a revolution in self-polishing hull coatings technology several decades later.

But International Marine Coatings latest self polishing copolymer (SPC) Intercept®8000 LPP incorporates the best features of TBT-based hull paints without the negatives.

Mike Hindmarsh, Business Development Manager, Newbuidling and Military, stresses the contribution that the two men made to coatings advancement.

“Alex and Sandy are the Godfathers of the latest self polishing copolymer coatings,” he says. “The properties which they discovered nearly 40 years ago have been formulated again in our latest SPC coating, Intercept®.”

Although outlawed in 2003, many ship operators swore by TBT-based coatings which had become the industry norm: they were tremendously effective in the prevention of fouling build-up. Unlike rosin-based systems, TBT based coatings had no leached layer to slow down the release of biocides – the reason why controlled depletion polymer (CDP) hull coatings  only work effectively up to 36 months.

The smoother the better

Crucially, TBT-based SPCs polished predictably over time, resulting in smoother hulls and less frictional resistance. This gave ship operators a clear picture of likely hull coatings maintenance in the future.

Robert Townsin, a naval architect with whom International® researchers have worked closely over the years, provides a general rule of thumb: for every 25 micron increase in hull roughness, there is approximately a 1% penalty in fuel consumption. Smoother hulls save money.

The predictability of TBT-based coatings performance gave ship operators much more flexibility on how long their ships could stay out of drydock. This consistency, meant coatings would perform for longer , resulting in a whole new era of fouling control management.

However, long before the application of TBT-based coatings was banned by the IMO in January 2003, International®’s polymer scientists had been working on a range of alternatives.

But try as they might and despite the pre-eminence of International®’s research team, its scientists could not reproduce the principal feature of TBT-based coatings which had won over the hearts and minds of so many ship operators – the fact that such coatings polished at a consistent rate over time. Their predictable antifouling performance had proved invaluable in planning ship maintenance strategies and drydocking intervals.

None of the replacement technologies – based on copper, zinc or silyl acrylates – offered the same consistency. Copper-based coatings, for example, tend to polish faster at the outset and slow down to linearity: silyl acrylate paints behave in just the opposite way, requiring a greater thickness of paint to allow for faster polishing towards the end of the docking cycle.

TBT-like linear polishing seemed unachievable.

Until now.

The Lubyon® revolution

A new polymer technology, with its roots stemming from research carried out by Alex Milne and Sandy Christie all those years ago, now offers ship operators the constancy and predictability in coatings performance which TBT replacements have so far failed to deliver.

The patented Lubyon® polymer is “super-hydrophilic”, meaning that it is water-loving – the surface swells on immersion, smoothing out imperfections. This ‘lubricious’ effect results in a low-friction surface which is smooth and slippery under water.

Patented by International®, the new polymeric coating offers a linear polishing rate with consistent biocide release. The super-hydrophilic surface reduces resistance, there is no leached layer and its performance is largely unaffected by water temperature.

In fact, Intercept®8000 LPP heralds a revolution in self-polishing copolymer hull coatings. In-service trials provided excellent results and early applications are generating positive feedback from customers.

Chinese coastal operator Shanghai Donghai Shipping, for example, selected Intercept®8000 LPP to replace a standard rosin based (CDP) antifouling on the hull of its 7,500 dwt tanker Dong Cheng You 16 which trades in a relatively high fouling challenge region on the Chinese coast. The owners report a one knot speed increase and an almost 10% cut in fuel consumption.

Hindmarsh is delighted, the results are very encouraging.

Meanwhile, Royal Caribbean has notched up a first with its choice of Intercept®8000 LPP and International®’s new top-of-the-range fluoropolymer antifouling, Intersleek®1100SR, for the hull of its Legend of the Seas.

Save money, cut fuel bills

Hindmarsh says that ship operators now have a fantastic new opportunity not only to save money by cutting fuel bills but also to take greater control over the management of hull performance over time.
“We can now offer the same level of predictable linear polishing performance which ship operators have missed since the days of TBT,” declares Hindmarsh. “This is a major watershed in SPC development.”

He also points out that fuel savings are potentially just as achievable when ships are slow-steaming as they are at full speed. In fact, he says, the percentage saving becomes greater at slower speeds though the actual value in dollars is less because less fuel is being consumed.

Although International®’s executives are expecting Intercept®8000 LPP to appeal initially to owners in a maintenance and repair context, they are also well aware of the importance of the ship construction market, particularly in the future.

“We must support the newbuild market,” says Hindmarsh. “And it’s important that Intercept® should be on shipyards’ standard specifications.”

Find out more about our performance pioneers and how they shaped the marine coatings industry >>> International Paint - The Performance Pioneers

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