Eighty-knot gales, 10m-high waves, pitchpoling, loneliness and ever-depleting food reserves… of all the challenges facing a single-handed non-stop circumnavigator you wouldn’t expect the humble barnacle to make the top 20, let alone the top five. And yet this lowly crustacean was a serious problem that came to dominate the latter stages of the 2018-19 Golden Globe Race.

The images of long-keeled hulls entirely encrusted with barnacles, like a kind of organic structure, are a grim enough sight for a cruising sailor, but it is unprecedented in a race. Uku Randmaa’s Rustler 36, One And All, was the worst affected of the Golden Globe Race fleet. He finished 3rd after almost 252 days of sailing.

The barnacle problem really came to light at the Hobart film drop. Race chairman Don McIntyre was there to meet Randmaa in Hobart. He said afterwards: “I’ve never seen anything this bad in my entire sailing life. I felt so sad waving goodbye knowing that they will continue to grow every day to the finish. He left with a best estimate drag penalty of 0.5-1 knot for every hour he is sailing. That’s 12-24 miles lost every day for 100 days!”

Fouling proved heavy on One And All. Photo: Christophe Favreau / PPL / GGR

By contrast, Golden Globe Race winner Jean-Luc Van Den Heede suffered from very little barnacle fouling, with just a few suicidal crustaceans attaching themselves above the waterline. Yet he was also sailing a Rustler 36 and followed the same route. What can explain the difference? Well, one clue lies in the antifouling preparation by each contestant.

According to Golden Globe Race media manager Barry Pickthall, Randmaa’s boat had just one coat of Seajet Shogun when it was hauled out in Les Sables d’Olonne before the race. “The boat had done several months with the 2017 OSTAR, and there was nothing left on.”

Contrast that with the approach of Van Den Heede, who applied four coats of Seajet – three base layers of self-polishing Shogun and a final topcoat of Platinum, which contains an anti-slime agent called zineb. “The idea was it would wear itself down during the 8,000 miles in the Atlantic and expose the second layer in the Southern Ocean,” explained Pickthall.

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Prior to departure, Van Den Heede also kept his hull covered with tarps – a technique popular in the 1970s, which resembles a 30ft tent drawn up around the boat’s hull containing chlorine to kill microorganisms that turn into biofouling.

A number of skippers reported problems with barnacles, despite having applied Coppercoat’s epoxy-based antifoul. A Coppercoat spokesperson pointed out that the company has no knowledge of how well the product was applied. Correct application requires five thin coats to be applied, wet-on-tacky, all in the same day in warm conditions.

“No competitors contacted us before the race to use Coppercoat,” said Ewan Clarke of Coppercoat. “We heard of one that didn’t do it properly.” Antifouling does seem to have been a somewhat neglected part of preparations for some Golden Globe Race entrants.

Antifouling coatings must be scrupulously applied to stand a chance of resisting barnacle growth. Photo: Coppercoat

“There were some competitors whose pre-race preparation in terms of antifouling was pretty poor,” Clarke added. “Then it’s not a fault of the antifoul; just bad antifoul management. It’s like going on a long journey and running out of fuel. It’s pretty commonsense.”

Of course, these are issues that face cruising sailors as well. With average speeds of less than 6 knots, the fleet behaved much more like bluewater cruisers than modern race boats. And it’s worth noting that barnacle fouling problems were widely reported in lots of cruising grounds last year, not just the Southern Ocean.

The life cycle of a barnacle

Barnacles feed on plankton in their early life stages, when they are free-floating in the water column. It is only in their final life stage that they settle onto solid surfaces – like boat hulls.

“The barnacle fouling levels we experience today are heavily influenced by environmental conditions over the last six months or so,” explained Dr Tom Vance, manager of Plymouth Marine Laboratory’s Centre for Marine Biofouling and Corrosion.

“Based on our observations from surface waters off the coast of Plymouth, the summer and autumn of 2018 experienced higher than normal sea surface temperatures and temperatures at 50m depth. This is very likely to increase the growth rates of the food that the barnacle larvae will feed on, and rates of the barnacle larvae themselves.”

Once barnacles get a grip on a marine surface they can multiply rapidly. Acorn barnacles like these are the most common in UK waters

In UK waters, most barnacles on yacht hulls are acorn barnacles. But in other parts of the world, and in more exposed UK waters, different species predominate. Those collected so easily by the Golden Globe Race boats are thought to be goose barnacles, which are known to be more aggressive foulers.

“Goose barnacles grow like the clappers,” said Dr Vance. “It’s almost unbelievable. They spend a lot of time in the water column and will settle on almost anything. If you’re doing two to six knots – whale speed – then you’re a prime target. It’s settle or die.”

If you’re unlucky enough to run into a posse of goose barnacles, then, the only option may be scraping the hull before it’s too late. Since the banning of the ruthlessly effective tributyltin in the 1980s, the environmental restrictions on antifouling have been steadily tightened.

“With the latest Biocides and Pesticides Register laws, antifouls have had to be reformulated and most are now less effective than they used to be years ago,” said Coppercoat’s Ewan Clarke. “People have to accept the fact that cleaning their boats more frequently is likely to be the new normal.”

Scraping is the only realistic option for cleaning barnacles from a hull. Photo: Boris Senatorov / PPL / GGR

All barnacles leave behind thin discs on the hull, which should be fully removed because they contain pheromones, which will attract fresh encrustations. On harder coatings, like Coppercoat, you can lightly sand them away or even apply a mild acid (patio cleaner is recommended) to dissolve them.

Racing antifoul is also hard, to make the boat more slippery in the water, but typically requires scrubbing off every month or so. Your average cruiser might feel that diving over the side with a brush each month is beyond the pale. And with the slower speeds of cruising yachts, fouling build up is bound to occur quickly on a hard racing finish.

For faster boats another option is fouling release coatings (FRCs), which are usually silicon based. Their mission is to prevent marine fouling from forming a strong bond to your hull in the first place.

FRCs will self-clean at a speed above around seven knots – fine if you’re in a fast catamaran or a TP52, but not so realistic for bluewater cruisers. These finishes will still require regular scraping or brushing.

That leaves most cruisers with three distinct groups of paints: everyday ablative antifoul, self-polishing antifoul and Coppercoat. The first two work by wearing down slowly as water passes over them, constantly revealing fresh biocide.

Photo: Hempel

Longevity will depend on the quality of the paint and the number of layers you apply. Cheaper ablatives are rosin-based and erode very quickly – you’d be lucky to get a season of hard cruising from them. Better so-called self-polishing products, like International’s Micron, react at a constant rate with the water to control biocide availability whether the boat is moving or not.

Coppercoat is a little different, because it is based on a hard epoxy finish that is closer to a racing paint. It contains a high level of fine copper dust – 2kg per litre – which is why it can protect hulls for ten years and more in optimal conditions.

Correct application is vital

But if there is a key lesson to learn from the Golden Globe Race, it is this: whatever antifoul you choose, make sure it is correctly applied.

“Read the data sheets and make sure of the correct preparation in the right environment and that the correct amount of coats are applied,” says Jamie Smith of Marineware, which distributes International and Nautix antifouling. “Adding an extra coat to the waterline and other high wear areas can help also.”

This is borne out by Van Den Heede’s successful approach, although he admits that he got a little lucky. “I didn’t study the subject hard enough,” he told me. “Preparation is the key in this sort of adventure.”