October 11, 2018

Anti-fouling your boat: Everything you need to know - Motorboat &. Yachting Magazine Nov 2014

Anti-fouling your boat: Everything you need to know 

Motorboat and Yachting Magazine Nov 2014

In this feature, we explain everything you’ve ever wanted to know about anti-fouling, plus some things which you didn’t know you wanted to know: like can you mix your own copper paints? And how did Columbus anti-foul his boats?

What are the main types of fouling?

Fouling, or more accurately ‘biofouling’, is the build-up of plant and animal life that occurs on all submerged structures, from rocks to oil rigs and boat hulls.

These are generally split up into two subdivisions: microfouling and macrofouling. Microfouling is made up of microscopic bio-organisms, such as slime, bacteria and other small algal life forms.

Macrofouling is the bigger stuff that us boaters tend to get worked up about, such as barnacles, muscles, tubeworm, sea squirts and seaweed.

Why should I worry about it?

Because any significant growth of fouling has an immediate effect on your boat’s performance and its fuel efficiency.

On planing powerboats even a light build-up of fouling can knock five knots off your top speed and increase fuel consumption by 30%. Heavier growth may prevent a boat from planing altogether.

Does fouling vary from place to place?

Absolutely – from place to place and even year to year, according to the water temperature, its salinity, the level of sunlight, the quantity of nutrients and countless other factors.

Generally speaking, the higher the water temperature, the greater the growth, hence the reason fouling is so bad in the Mediterannean. There are variations in the UK too, with local boaters invariably claiming that their haunt is the worst.

Has it always been a problem?

Yes. And it was arguably even more of a problem to the lumbering sailing ships of yesteryear. Heavy fouling or the lack of it could be a matter of life or death during the slow-motion naval battles that they engaged in.

How did they cope?

In the early days careening was the preferred method. This involved tipping the ship on its side, lighting small fires under the hull, then scraping off the softened pitch and fouling by hand.

Pitch, tar and even whale grease were favoured by the likes of Christopher Columbus and Sir Walter Raleigh. The introduction of metal sheathing, first with lead and then copper and zinc, didn’t happen until the 1700s.

What other types of anti-fouling were tried?

You name it, someone has tried it. Patent records have been filed for everything from ground glass to arsenic, red lead, sulphur, and even guano!

History doesn’t relate which ones were the most effective, suffice it to say that bird poo doesn’t feature on many chandlers’ stocklists these days.

What are the current options?

The three main choices for leisure boaters are to paint it with some form of eroding anti-fouling, to coat it with a semi-permanent copper treatment, and to prevent build up of growth by keeping it clear of the water or regular scrubbing of the hull.

Which is best?

Theoretically, the last. A polished gel-coat will slice through the water with less drag than a hull painted with a soft, copper oxide-based antifouling.

This means it will be faster and more fuel efficient (a 34-knot boat can lose up to two knots from paint alone). It is also the most environmentally sound option.

But unless you own a boat you can keep out of the water on a lift or dry-stacking system, it is also a pain in the butt. Even a new polished hull will need scrubbing down every few weeks, while a scratched or pitted one will attract growth in a matter of days.

How do the other systems work?

Anti-fouling paints and semi-permanent treatments rely on a variety of biocides to deter and if necessary kill organic matter.

The main biocide in paints is usually a compound of copper, such as copper oxide or copper thiocyanate, which is boosted by co-biocides targeting specific types of algae and slime.

Longer-term treatments, such as those offered by Cuprotect (pictured below) and Coppercoat, rely on copper alone, usually in the form of tiny copper granules sprayed onto or suspended in a non-eroding resin coating.

Which system works best?

There is no definitive answer to this but as a very broad generalisation, a conventional eroding anti-fouling paint tends to be very effective initially but then becomes gradually less so over time, while semi-permanent coatings should maintain a similar, but arguably slightly less effective level of performance year after year.

Why does anti-fouling paint become less effective over time?

Because nearly all ablative paints work in a similar way. The active biocides, such as cuprous oxide, and the other algaecides are held in an inert resin paint matrix (usually made up of binders, solvents, pigments and small amounts of other additives).

Once submerged in water the active biocides gradually leach out of the paint matrix to deter any growth, leaving behind a honeycomb of ‘dead’ paint.

Most of this will be worn away by the action of the boat moving through the water (or in tidal berths, the water moving past the boat) to reveal a fresh layer of biocide-laden paint.

The problems tend to occur when boats are left unused for extended periods of time in non-tidal berths. This allows a thicker layer of dead paint to form, which slime and barnacles can settle on.

Do some anti-fouling paints last longer than others?

Yes. By fine-tuning the leach rate of the biocides and the eroding properties of the paint matrix, manufacturers can extend the life of paint to two or more seasons. However, this doesn’t get around the problem of boats being left unused for long periods of time.

Are there any exceptions to this rule?

Yes. True self-polishing copolymers, such as the tributyl tin (TBT) paints of the 1980s, maintain the same high level of performance regardless of whether the boat is static or moving.

This is because they don’t rely on the physical action of water passing the hull to erode away the paint and leach out the biocides, but on a chemical reaction with the water itself.

The active biocide, tributyl tin oxide, is a colourless soluble product that is chemically part of the paint matrix itself. As the TBT is exposed to water it reacts to form a soluble compound that dissolves into the water.

This exposes a brand-new layer of fresh biocide-laden paint and means that performance is consistent even when the boat is lying in the marina.

It also prevents the annual build-up of paint, can be brightly coloured or left clear, and may even make older boats faster by smoothing out imperfections in the hull surface. It was the Holy Grail of anti-fouling paints!

So why can’t I buy TBT-based paints now?

TBT settled in high enough concentrations around marinas and estuaries to cause lasting damage to the marine life, leading to a ban on TBTs for use on leisure vessels under 25m in the UK and Holland during the late 1980s. This was adopted by other countries around the world culminating in a worldwide ban in 2002.

Does that mean today’s anti-fouling paints are less effective than they used to be?

Although manufacturers are loathe to admit it, that probably is the case. Some owners stockpiled TBT paints before they were banned and rumours persist that it may still be possible to track down supplies from unscrupulous sources.

Are they likely to ban copper?

Probably not, though Holland has tried to ban it once and there are restrictions on its use in Sweden. Copper is naturally occurring in water and in small quantities actually forms part of most marine organisms’ diet. It also disperses more readily than TBTs and rapidly complexes into harmless copper compounds.

So how can copper act as a biocide?

When it is ingested in large enough quantities it becomes toxic. Contrary to popular belief, it is not copper itself or copper oxide that is the most active element of the biocide, it is the cuprous ion (Cu+). This ion is formed when copper oxide comes into contact with seawater in the presence of oxygen.

Because this ion is easily absorbed by organic matter, it will eventually overwhelm the natural biological processes of the organisms.

However, the thin barrier of copper ions that surround the boat’s hull is usually enough to dissuade barnacles and weed from even trying to attach themselves to the painted surface.

As the cupric ion complexes and becomes more dilute, fouling can happily survive just inches away. That’s why even the smallest areas of unpainted hull can rapidly attract a thick layer of healthy barnacles.

Is there a TBT-free self-polishing paint?

Although you may find the term ‘self-polishing’ on paints, they may simply be eroding (otherwise known as ‘ablative’) paints that have a self-smoothing action, rather than true copolymers.

Jotun has a new TBT-free self-polishing product in their commercial range of anti-fouling paints. Seajet also claims that its Platinum 039 is a genuine self-polishing paint.

Why can’t all copper-based paints be used on outdrives and propellers?

Copper and copper oxide can promote electrolytic corrosion of aluminium alloys. That said, some hard anti-foulings like International Trilux and Seajet Emperor are safe to use because copper thiocyanate does not cause the same problem.

How come semi-permanent coatings stay active year after year?

Instead of using a leaching copper compound and an eroding paint matrix, they use pure copper (or a copper zinc alloy) in its metal form set in a much harder coating such as epoxy resin.

The tiny copper granules are either held in suspension in the paint (in systems like Coppercoat) or sprayed onto a resin surface while it is still tacky (Cuprotect).

It still works the same way, in as far as the copper metal once submerged in water starts to oxidise and then the cuprous oxide leaches copper ions into the water.

This process is much slower than the leaching of copper oxide from eroding paints and has the potential to last much longer.

However, erosion does still happen, which is why it is sometimes necessary to refresh them with an annual wash-off and light abrasion of the copper/resin mix to expose a fresh layer of copper. Most of these coatings have a quoted life expectancy of over ten years and plenty of users swear by them.

Why doesn’t everyone use a semi-permanent coating?

In the short term they are more expensive than conventional anti-foulings, harder to apply (you need to completely scrape or blast off any old antifouling), only available in one colour (brown when fresh, greeny/blue when oxidised), and seem to work better for some people than others. This may be due to poor application, insufficient burnishing between seasons or local conditions.

A patchy history of companies coming and going, as well as confusion over the types of copper treatment (copper tiles were briefly tried and then withdrawn), hasn’t helped customer confidence either.

Any other systems on the horizon?

A number of manufacturers are experimenting with so-called ‘low surface energy’ products. These are usually non-stick Teflon or soft silicone-based coatings, which have such a smooth surface that fouling struggles to get a grip on it and is soon washed away by the water flowing past.

While these have proved effective on container ships, which rarely stop for more than a few days at a time, they are not generally so suitable for craft that spend large amounts of time stationary and may be vulnerable to surface damage from fenders, lifting strops and sediment.

Other possibilities include ultra-hard ceramic surfaces, which can be regularly scrubbed clean, and even nano-surfaces, which can stop organic matter from sticking to them through specially textured patterns.

So what’s the difference between a hard antifouling paint and a soft one?

A soft paint erodes more quickly than a hard one. In the case of fast motor boats, the action of the boat passing through the water can cause a soft anti-fouling to erode too quickly, especially along areas of high pressure such as planing surfaces, chine edges and where the crane’s lifting strops have rubbed.

This could wear away the fresh anti-fouling and expose untreated or exhausted layers of old anti-fouling.

Hard anti-fouling tends to have a smoother finish fresh from the pot and a greater choice of bright colours, but may not be so effective when the boat isn’t being used.

Does that mean fast motor boats should always use a hard antifouling?

Not necessarily. If you don’t use your boat that often or make sure you apply extra layers in areas of high wear, then a soft anti-fouling can be used and may prove more effective because of its faster leaching rate.

I use a base layer of hard anti-fouling on my 23ft sports cuddy, which I paint over with an extra coat or two of soft anti-fouling.

Why is it so expensive?

Partly because of the cost of the raw materials. Testing procedures aren’t cheap and finally every new anti-fouling product has to go through a long and costly type-approval process at the Health & Safety Executive.

Is it worth paying a premium for a well-known brand of paint?

The key active ingredients are unlikely to differ but the ratios, boosters and additives, which affect things like viscosity, flow rate, coverage and erosion will vary, as will after-sales support and advice.

Comparative tests can throw up different results, depending on where and how they were performed. Lesser-known brands can perform well, but big firms like International have multiple-testing sites (pictured below) where products are continually tweaked.

What about DIY brews that use copper granules, chilli powder and the like?

Technically, it is illegal to use any anti-fouling product that has not been approved by the Health & Safety Executive. However, in practice we have never heard of anyone being challenged on the matter. How well they work is another matter.

You can take it as read that chilli is a non-starter. Homebrews based on adding copper granules to conventional anti-fouling paints have a better chance of success and we know of several MBY readers who swear by them.

One owner recommends 250-micron copper granules mixed with International Trilux hard anti-fouling at a ratio of 1kg copper powder to 1-litre Trilux. It is essential to regularly mix the brew, as the copper will quickly slump out of suspension.

Bear in mind that not only is it technically illegal to make your own anti-fouling but that there is also a limit to the amount of copper allowed in anti-foulings, which these brews may well be exceeding.

The manufacturers and copper-based coating suppliers we spoke to were sceptical, pointing out that it may adversely affect the coverage and adhesion of the base paint and questioning whether it was the added copper or the original anti-fouling doing the work.

How do I know what to use?

Most of the well-known brands of paint have product guides, websites or even helplines you can turn to for advice. It is important when overpainting another product to ensure the two are compatible.

Trying to second-guess which of the dozens of products out there will work best for your circumstances is almost impossible.

It makes more sense to concentrate on doing a really good job of applying it than worrying too much about the precise make or brand of paint.

If you prepare the surface properly, paint on enough coats at the recommended thickness with extra layers in the key areas, the chances are it will do a decent job.


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