Sailing Today - What Antifouling Should we Buy - April 2008

No one in their right mind enjoys buying antifouling.  That’s why apocryphal tales of cheap and effective home made concoctions are so appealing.  There were the jolly West Country (or was it East Coast) fishermen who, legend has it, used a mixture of black varnish (a crude tar-based paint) and Jeyes Fluid (a disinfectant) plus a few dozen egg shells, which, they say, acted as an emulsifier and bound the evil mixture together.  To add romance to the story, this simple and inexpensive preparation was mixed in old, washed-up oil drums and heated over driftwood on the beach.  Whether they drank cider and sang sea shanties at the same time is unknown, but highly likely.

More recently, it’s said that yachtsmen have spiced up conventional products with everything from pesticides and antibiotics, to diesel and, curiously perhaps, chilli powder.  Even the manufacturers themselves have experimented.  As I recall, there was once something called Hot Bottom, which used cayenne pepper, but I imagine it was the copper in it that really did the business.  The real risk of fiddling about on your own, of course, is the potential risk to you, your boat and the environment, so it’s probably not such a good idea. 

Back in the real world, I’m afraid it’s a question of accepting the obvious fact that paint companies have invested huge amounts of money and employed the services of numerous clever chemists to develop their products.  We must also acknowledge the unwelcome fact that the materials they use are far from cheap and getting more expensive by the minute.  The price of copper, for instance, has increased by about 300 per cent in the last five years.

In the final analysis, whichever way you look at it, fouling is a difficult and costly problem to deal with and there’s no easy way out of it.  At the heart of the matter is the sheer complexity and nature of the assault on boat’s bottoms.  Antifouling paint must deter both plant and animal life whose sole purpose it seems is to make a thorough nuisance of itself.

The results of the enemy action are plain for all to see.  It causes drag, adds weight and can affect the way a boat handles.  Over time it can even attack the basic structure of the boat itself.

It all starts within seconds – as soon as your boat hits the water in fact.  There’s an immediate accumulation of dissolved organic matter and molecules that quickly settles down, inviting a rapid build up of sticky mucopolysaccharides or slime to you and me.

Surprisingly, these primitive forms of low life are far from push overs, partly because, in close up, they consist of tiny interwoven, interlocking filaments.  Some varieties are such battle hardened show offs that they apparently shrug off a dose of cuprous oxide and, for all we know, may positively enjoy it. 

These microscopic creatures – or vegetables – also provide the ideal foothold for more serious players like the numerous types of weed, some of which are predatory and use their tentacles to trap unsuspecting plankton that might be passing by.  Plants of course tend to thrive on sunlight, which is why such fouling is often most evident near the waterline.  Animal attachment on the other hand prefer to operate in the dark, often right down near the keel where they can work without being seen.  People who make a study of such things usually differentiate between ‘soft’ and ‘hard’ fouling organisms.  The soft variety includes a few things you’ve probably heard of, such as algae and kelp, and the others – diatoms, hydrides, hydroids, bryozoans and protozoans etc – that you haven’t and sound like extras in a second rate, sci-fi horror movie.  In the hard camp are tubeworms and molluscs – and our old chum the barnacle, which is probably the most insistent of all.  The well-known acorn variety, for example, arrives in egg form and attaches itself to unprotected surfaces with the force of a superglue.  As a consequence such is its incredible tenacity, it can etch its way into paint systems and eventually damage gel coats if allowed to make itself at home.  For the same reason, barnacles should also be removed with care and the calcium deposits they leave behind removed before repainting.

In all, according to the experts, there are over 4,000 different types of marine fouling species, which gives you some idea of what we’re up against.  Or, to be more accurate, what the manufacturers are up against.

Traditional Remedies

For many years the classic approach to the problem, at least for cruising boats, is a soft, relatively straightforward matrix containing cuprous oxide biocide set in rosin gum that slowly dissolved in water and gradually leaches out during the course of a season.  The most obvious problem here is the fact, that because the reaction leaves a hydrolysed layer behind, the release rate tends to show down gradually, so its effectiveness decreases.  That’s why manufacturers recommend a light rub down (using water and wet or dry paper) every year.  Otherwise after a few seasons, the subsequent build-up of these honeycomb-like residues must be completely removed to provide a sound, even surface for repainting, then the process can start all over again.  However, annual pressure washing can go a long way towards reducing if not totally eliminating the build-up problem.  Another possible drawback is the necessity to launch shortly after the paint has been applied – and the fact that the release rate is relatively uncontrolled.  However, for all that, these well-proven First Generation or traditional, hydration type antifoulings are still available and though far from cutting edge, are relatively inexpensive and particularly popular with fishermen whose boats get plenty of regular use. 

Then the boffins got clever.  By suing a carefully contrived combination of two resins, only one of which was soluble, they found they could control the reaction to produce a steady and even release rate.  These self-polishing copolymers (SPC’s) originally contained TBT (tributyltin), which proved incredibly successful in a huge variety of different environments.  It could also be used safely on aluminium.  There was only one drawback.  TBT is highly toxic and had an adverse effect on certain kinds of shellfish.

The result was a Europe-wide ban in 1987 that made its use illegal on boats under 25m.

Even so, TBT has still been available in certain areas of the world, notably parts of the Caribbean, though following recent ratification of the International Convention on the Control of Harmful Antifouling Systems on Ships (AFS) Treaty by 27 countries, it will be universally outlawed after September this year.

The European Commission also outlawed TBT on all vessels using EU ports with effect from 1 January this year.

The trend is undoubtedly towards less toxic alternatives.  Even copper which replaced TBT, is under threat.  Both Sweden and Denmark have imposed legal limits in certain areas on leach rates according to the size of boat, for example, but while the pressures are real, based on the evidence presented by ICOMIA at least, it’s unlikely that the European Commission will recommend a total ban when it makes its decision towards the end of next year.  Naturally enough though, such moves have focused the minds of the manufacturers.  It’s also the reason that these days controlled solubility or self-polishing copolymers are the obvious choice.  When the outermost layer of paint dissolves, it not only uncovers another film of biocide underneath, but also carriers away any animal or plant life that might have attached itself.  This is particularly significant, because it means the paint firms can get away with using less biocide – which is better all round.  Also, because they gradually wash away, these paints leave less behind than more traditional treatments and for that reason require less work at the end of the season.

As a bonus, copolymers are generally easier to apply and have greater covering characteristics, so you can actually use less of the stuff.  Even better, the latest concoctions are probably still more effective than the old and more vaunted TBT.

Most manufacturers offer a choice of copolymer products, typically for low, medium or high fouling areas.

Ablative systems are similar and belong in the same category, but rely more on a reaction with the surrounding water.  SPC’s and controlled solubility antifouling on the other hand provide the same kind of measured protection whether the boat is on the mooring or underway.

If this weren’t enough, at the same time, manufacturers have been trying to reduce the use of organic solvents like xylene, which can also be harmful.  Instead, they’ve introduced expensive, high performance waterborne antifouling that package the biocide in an emulsion, which evaporated leaving a hard film behind.

The chemistry is extremely complicated, but revolves around the use of film-forming liquid resins made from polymers and silica-coated copper.  The slight downside here is the fact that you can’t apply the stuff when it’s damp or raining.

Most erodible antifoulings use cuprous oxide, but some rely on cuprous thiocyanate, which is more expensive, but means you can use brighter colours.  With the correct preparation and suitable primers this ‘milder’ form of copper can even be used on aluminium – and is often found in antifouling treatments for propellers and outdrives.

Most if not all copolymers also contain small quantities of booster biuocides with such impressive names as zinc pyrithione, dichlofluandid and the awesome-sounding zineb – one even does away with copper altogether and uses the action of hydrogen peroxide.

The Hard Choice

So called ‘hard’ antifoulings, the other obvious alternative, is one much favoured by the racing fraternity in search of that extra tenth of a knot, because you can scrub it during the season.  Most use the same kind of ingredients as self-polishing varieties, but in different ratios.  For instance, there would invariably be more insoluble than soluble resins to maintain a more stable finish.  The way their biocides work is generally known as ‘contact leaching’, which uses a porous film saturated with biocides.  As one particle is dissolved, the particle behind it is exposed and takes its place, leaving a hard surface underneath.

Which Category

Having looked at the options, the next job is to decide which type is best for you.  As we’ve seen already, if your boat is made of aluminium, you can’t use an antifouling with cuprous oxide (unless you use a 400 micron thick epoxy barrier coat), because the two metals will react in salt water causing electrolysis and corrosion.  Steel is another slightly special case and may need a special primer – largely because of the increasing problem with stray currents in marinas.  This particular problem, which can throw off epoxies as well as copper antifouling, is often made worse by the amount of electronic equipment people fit these days.

For most GRP boats, however, the most likely choice is a modern self-polishing or controlled release antifouling that’s relatively easy to apply – though, ideally you do need a reasonably nice day without too much wind.

Long Life Antifouling?

If you want to avoid annual repainting, you might get away with it if you use several coats of a controlled solubility product, but as a rule the manufacturers don’t really recommend it.

Instead, they suggest you use a specially formulated multi-season copolymer antifouling with extra biocides designed to last for two years or longer.

Another alternative is one of the copper-rich concoctions, some of which use water-miscible epoxies, combined with spherical copper powder, which sheds itself at a rate of about two microns a year.  Given the fact that a standard treatment might contain  250 microns it’s understandable that the makers should claim a lifespan of 10 years and claim that some of their client’s boats have survived happily for some 15 years without further treatment.

Others use copper-nickel granules sprayed onto freshly applied resin, which, they claim, produces a hard, long lasting coating without additional booster biocides.

One possible drawback, I suppose, is the huge amount of copper they use, particularly at a time when the move is towards less toxic alternatives.  The manufacturers’ argument would be that the release is slow and carefully controlled.  

Slippery Substitutes

Alternatively, of course, some preparations use super slippery components such as Teflon.  Clearly this doesn’t kill off micro-organisms in the same way, which is why most of them also contain biocides, but it will create a really smooth, low friction surface, which can be burnished, that makes their removal considerably easier – as long as you don’t leave it too long.   A boat that remains on the moorings and never gets used will almost inevitably suffer an increasingly stubborn build-up.

On the subject of hard finishes in general, while we tend to think of them as synonymous with racing, they have other applications too.  As a case in point, they make particular sense if your boat dries out at low water.  A hard antifouling will stand up to bumps and knocks and general wear, tear and abrasion far better than the softer types.  That’s why it’s also suitable for trailer-sailers or boats that are dry berthed ashore and launched every time the owner goes afloat. 

Let’s not forget that the kinds of erodible paints we’ve been talking about also have their limitations.  It’s best not to use them on boats that regularly travel at 25kn or more, because, as you might imagine, high speeds will hasten the antifouling’s demise, which will simply wash away faster than its makers intend.

It’s equally important to be aware that different paints are formulated for different parts of the world, so if you’re planning to move to the tropics, you might want something designed to work in higher temperatures   The same principle goes for boats kept in fresh rather than salt water.  In each case, it’s a question of the right coating for the job. 

Which Is Best?

Having looked at all the various options, the next job is deciding which product is right for you.  As we’ve seen, and at the risk of repetition, for those of us with GRP hulled boats, unless we decide to opt for a long-life copper-rich treatment, it’s largely a question of deciding whether we want a hard or soft antifouling.  As we’ve seen, hard antifoulings are ideal for racers but also for boats that are kept ashore or in mud berths.  For the rest of us the basic choice is whether we go for a regular controlled solubility copolymer or a more expensive, high performance, self-polishing alternative.  These state-of-the-art products often come in two component form, - either with additional booster biocides or special activators.

Judging by anecdotal reports from owners, there’s no question that you get what you pay for, but, bearing in mind the big difference in price, it’s still worth asking around, because in some areas a controlled solubility product may work just as well as the more expensive self polishing alternative.  You might even get away with one coat – though, I’ve absolutely no doubt at all that the manufacturers would vehemently disagree.

On the other hand, you might think that the best antifouling paint would simply be the one with the most copper in it – which in turn means the one with the highest specific gravity – and to be honest, some overseas manufacturers encourage customers to think that way.  That’s why they flag up the copper percentage so boldly.  If you go along with that, it’s a case of the heavier the paint the better, but not everyone agrees.  For a start, many mid-range products contain roughly similar amounts of copper and the drive now is towards producing the most effective combination of biocides and co-biocides (or boosters) and even reducing them, so arguably, it’s more a question of matching a particular blend of ingredients to a particular set of circumstances.

The snag is that what works in one area one year may be less effective the next.  Among other things, it depends on the temperature of the sea, it’s salinity and even the amount of pollution.   Even so, it’s still worth comparing notes with owners of similar boats in your area to see what seems to work best.

Tough Times

As I said at the beginning, we all complain about the cost of antifouling, but it’s worth remembering that the manufacturers are trying to conduct an almost impossible balancing act.  While we, the consumers, want the most powerful product at the cheapest possible price, environmentalists are demanding ever tighter legislation on the use of anything that might conceivably have the slightest detrimental effect on marine habitats.

In Europe, the Biocidal Products Directive (BPD), which came into force eight years ago, requires two regulatory submissions before a biocidal product can be marketed, each of which needs a separate dossier for every product, containing information on its biocidal efficacy, toxicological and ecotoxicological properties.

So, to put it bluntly, everything the manufacturers do is subject to the closest scrutiny.

Whatever you think about the paint companies, trying to keep everyone happy is a difficult trick to pull off.