The fact that smooth hulls save fuel has been a key message from International Paint for years. But understanding how and why marine organisms attach to the often hard-to-reach underwater areas of ships is a complex scientific challenge.

Now, leading researchers are focusing on “slime”, a generic term covering many types of marine organisms which, so far, have defied man’s attempts to stop them settling on the underwater hulls of vessels. These researchers include famous scientists across the world, such as hydrodynamist Professor Mike Schultz at the US Naval Academy and biofouling specialist Professor Geoff Swain at the Florida Institute of Technology.

Other scientists at world-leading academic institutions, researchers in the US Navy, and chemists and marine biologists at International Paint’s R&D facility in Felling, UK, are also focusing on research into slime.

Until recently, macro-fouling – involving both plant and animal organisms – was their main focus. A seriously macro-fouled ship’s hull can increase resistance through the water by as much as 40%. And even in the days of cheap bunkers, most ship operators were clear that hulls had to be kept clear of organisms such as barnacles and weed.
 

Growing their own slime
 

But as fuel costs have continued to climb, International Paint has turned its attention to less obvious organisms, including “slime”, a complex community of bacteria and diatoms.

Slime - A Diverse Industry Challenge

Few, if any, have done more to understand the science of slime in a practical ship operating context than International Paint where a team of chemists, marine biologists and polymer specialists are, quite literally, growing their own slime. As a result, they are right at the forefront of marine fouling research.

David Williams is Research Manager at International Paint and has spent 15 years in fouling control. He runs the company’s Technology Centre in Felling, UK, where some 30 chemists, marine biologists and other multi-disciplined scientists address the challenges of fouling control – with a particular focus recently on slime. A key member of the team is Jennifer Longyear, a marine biologist, partly funded by the UK’s Royal Commission for the Exhibition of 1851.

The Royal Commission for the Exhibition of 1851 was established in 1850 by Her Majesty Queen Victoria to organise the Great Exhibition and fellowships and grants to pure research in science and engineering, applied research in industry, industrial design and other projects. Jennifer’s research will lead to a far clearer picture of the build-up of slime over time.
 

Big competition
 

Just how closely David and Jennifer and the team are involved in “understanding the enemy” is evident from the way in which he describes the Centre’s ongoing research into slime. “It’s a big competition out there,” he says, “and every organism wants to get on to that underwater surface and stay there. We have to understand how and why, and find ways to stop them.”

“With modern hull coatings available today,” he continues, “ship owners and operators don’t expect macro-fouling. That’s a given! But what about slime?”

“It’s a marine bio-film comprising millions of organisms which nobody knows much about, and feedback from customers led us to believe that we had to research slime as a matter of urgency,” explains David. “We said we needed a whole community of slime and so developed a farm where we grow our own. Today, we have a marine biology facility where we grow bacteria and diatoms which change every day. And we’re focusing on new technologies which work against all bacteria, algae and diatoms which, to a ship operator or his superintendent, are simply slime.”

Its effects are only too clear to the operators of some vessel types, and can represent a penalty of several percentage points when it comes to bunker consumption. On a big containership, this could be several tonnes of fuel a day, running into thousands of dollars. Across a fleet, this could mean millions of dollars in fuel and increases in emissions every year.
 

New challenges
 

Tackling the slime issue has meant plenty of new challenges. Diatoms have various unique characteristics compared with other forms of marine fouling. For a start, any surface submerged in sea water develops a bio-film in minutes. Invisible to the naked eye, this has the potential to start increasing hull resistance immediately.

According to International Paint’s Dataplan scheme – which records the application of coatings and their subsequent performance on the hulls of more than 200,000 vessels – there was no statistical difference between the development of slime on biocidal or non-biocidal coatings. In other words, it’s much more tenacious than other forms of fouling.

A third issue which International’s scientists have had to tackle is the fact that slime develops on any underwater surface, regardless of speed, and is difficult to remove under normal operations.
 

Extensive tests
 

David and his team have worked closely with many external institutions, thereby cutting the time required for tests and trials by a multiple. Communities of slime have been harvested from rocks, ships and other underwater surfaces, put into an incubator in the International Paint Technology Centre and given plenty of food.

Different types grow at different speeds but slimed fouling control coating test slides developed at the farm can be quickly assessed for their foul release capabilities.

Intersleek_®1100SR - Slime Release Performance

“We have managed to test more than 140 different coating formulations within 18 months,” says David, “ and within a month, we can test the performance of potential new products against our existing ones.”
 

“Initiative won’t stop”
 

David is clearly excited by his team’s recent achievements, particularly the fact that the slime farm has hastened the drive for new super-efficient hull coatings the first of which, Intersleek®1100SRwith unique slime release capabilities, was recently launched. But there is no sign of complacency.

“Setting up a slime farm is not easy,” he says. “We may be one step ahead today, but we intend to stay one step ahead tomorrow too. Our slime initiative won’t stop – what makes it, what stops it and how can we prevent it sticking to ships’ hulls?”