Adam Fiander and Hugo Andreae test eight antifouling products on a regularly used Hardy 42 motorboat to find out which is the best antifouling paint on the market right now…

Last June we coated the hull of a Hardy Commodore 42 with eight of the best antifouling paint products. The motorboat Raymariner, which is the test boat for Raymarine, is based in the Solent and is used three or four times a week for trialling the company’s electronics.

The aim of the test was to compare traditional copper-based annual antifouling paints with a number of longer lasting and more environmentally sensitive alternatives.

We applied three non-copper antifouling paints and three traditional eroding paints plus IP Ultra 300, which is a hard coating, and Coppercoat, which is a non-eroding copper-epoxy coating.

Raymariner was lifted in January 2022 to have a transducer replaced, so we took the opportunity to compare the results after seven months of submersion.

Tightening antifouling paint regulations

These days, many of our buying decisions are influenced by our desire to be mindful of the environment. Antifouling paint is no different, and the Biocidal Products Regulation means manufacturers are subject to ever tightening regulations controlling the substances they are allowed to use.

Copper is still the most widely used biocide in antifouling paints. Described, variously as copper powder, dicopper oxide or cuprous oxide, copper represents anywhere from 25% to 55% of the volume solids of many formulations.

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BEFORE: As Raymariner looked when she was launched in June 2021

This is suspended in a paint matrix that gradually erodes as water passes the hull, releasing biocide at controlled rates, depending upon whether it’s a hard or soft-eroding type. It is the build-up of these biocides in marinas, harbours and waterways that poses a risk to larger marine wildlife.

Coppercoat is the exception to the rule, because although it counts as a biocide, it uses copper granules set in hard epoxy resin that not only gives it a lifespan of 10 years or more but ensures that only minute quantities of copper are actually released into the water.

Alternative antifouling paints

As the net tightens some countries now ban the use of copper-based antifouling paints, so manufacturers are coming up with a number of biocide-free alternatives. Silicone based formulations – such as Seajet Bioclean, which we used on the PBO Project Boat (PBO February 2022) – are among the most promising alternatives.

These prevent fouling through the physical properties of their super smooth hydrophilic surface rather than biocidal action. In other words, the coating is simply too slippery for marine fouling to attach itself.

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AFTER: As she looked when she was lifted towards the end of January 2022

It’s all very well having strong eco-credentials but we wanted to find out if these silicone-based alternatives work in a range of different biofouling conditions. Do they, for example, stand up to the rough and tumble of the dry-stack, and will their multi-coat regimes and strict instructions for pot lifetimes and overcoating intervals appeal to the pressed-for-time DIY and professional user?

Since silicone based coatings work better on regularly used boats (as do self-polishing antifouls) Raymariner was the ideal test bed. For comparison purposes, however, we did paint a static panel to see how that fared. Antifouling paints need motion of water across the hull to work, so this was placed in a tidal area, and we’ll revisit it over a longer period of time.

High on slime

Last year’s hot and wet weather may well have contributed to the excessive build-up of slime that greeted us when the boat was lifted in January this year. As you can see from the pictures, slime coated all eight test stripes, some more than others. However, almost none of them showed any weed or shell growth, whereas the uncoated strips we left between some of the products were heavily encrusted.

You can see a full table of costs and specifications below but for the individual antifouling paint reviews we have quoted two prices. The first is our estimated price of the initial application to a typical 36ft boat (not our 42ft test boat), including the cost of any essential preparation work such as stripping and priming (but not labour or lifting costs).

The second is an estimated annualised cost calculated over a nominal six-year period to reflect the lengthier payback times of medium and long term treatments such as Silic One and Coppercoat.

The table doesn’t include labour costs and some coatings may of course last longer than their specified times, including the traditional ‘annual’ antifouling paints.

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Great for topsides, not so good underwater

8 of the best antifouling paints tested

Ceramic Pro

Type: Biocide-free ceramic based nano-coating
Preparation: Smooth bare gelcoat
Initial cost: POA, for above-water use only

In fairness to Ceramic Pro, they were keen to be involved in this test as much for their own ongoing research as for ours, to see if their protective ceramic coating designed primarily for use above the waterline, would also prevent fouling below it.

Hugo Andreae, editor of our sister title Motorboat and Yachting (who we jointly ran the test with), has used Ceramic Pro to good effect on his own boat.

The hydrophobic surface makes it easier to clean and it has become a popular treatment among professional boat valet and ‘detailing’ companies, who find it provides a tough and permanent barrier against salt-deposits, exhaust fumes, surface oxidation, staining, bird-droppings, and that ugly line of filth commonly seen around the boot-top, just above the waterline.

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BEFORE (left): Ceramic Pro looks great above the waterline. AFTER (right): But it didn’t seem to deter fouling below the waterline

It was hoped that this would also prevent fouling from attaching below the waterline, however the micro-organisms that lurk in the Solent’s tidal waters proved too persistent.

Even though the fouling was not too difficult to remove, shell growth and plant life had clearly taken hold and probably would have become worse over an even longer period of time.

Ceramic Pro told us pricing for boats is on a case-by-case basis and as the product was not successful as an antifouling it was not included in the results table below.

Buy it now from ceramicpro.co.uk

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Lasts for 10 years, but has a high initial cost

Coppercoat

Type: Non-eroding long term biocide
Preparation: Hull blasted back to bare GRP
Initial cost: £1,948
Annualised cost: £325 (£183 without shotblast preparation)

Coppercoat uses pure copper powder set in a hard epoxy coating that should last for at least 10 years and vastly reduce the amount of copper released into the water.
Coppercoat is a two-component epoxy that can only be applied to hulls that have been stripped back to bare gelcoat.

We used an antifoul removal firm to mineral-blast the test area but if you were to strip the hull yourself it would be much cheaper.

Each of Coppercoat’s five coats have to be applied wet-on-tacky. This effectively means it all has to be done during the course of a single day.

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BEFORE (left): Copper colour turns a greeny blue once immersed. AFTER (right): Some slime evident but no weed or barnacles

Once dry, the coating needs to be burnished with 400-grit paper to expose the copper and activate the coating. The only ongoing/annual maintenance required is to clean (typically pressure-wash) the boat from time to time.

The results show a similar level of protection to the other copper-biocide alternatives. There may be a little more slime than some but in fairness to Coppercoat, theirs is a slow-release long-term solution and seven months is barely one season’s worth of use.

The initial cost is higher than most, partly due to having to blast off old antifoul (brand new boats just need sanding), but its annualised cost after six years is much the same as traditional antifouling paint and it would carry on getting cheaper after that. Nor does this take into account the substantial saving on labour time.

Buy it now from coppercoat.com

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Silic One was the best performer, but it is fiddly to apply

Hempel Silic One

Editor’s choice – best in test

Type: Biocide-free medium term antifoul
Preparation: Hempel Light Primer (4 coats), Silic One Tie-Coat (1 coat)
Initial cost: £1,045
Annualised cost: £233

Silic One had the most stringent set of application instructions of our group. It’s strongly advised to apply it on to a stripped hull but, if the existing coating is in good order, a barrier coat of Hempel’s Silic Seal will enable the switch.

Commencing with Hempel’s two-component Light Primer, the bare surface must be built up with a minimum of four thin layers. Next, a tie-coat must be applied while the last coat of primer is still tacky.

After two hours the first of two coats of Silic One can be applied, the second a minimum of eight hours hours later, then a 16-hour minimum drying time before immersion.

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BEFORE (left): Smooth rubbery surface makes it hard for fouling to grip. AFTER (right): Impressive result – no weed, barnacles or even slime

If it sounds like an involved process that’s because it is, taking nearly three days from start to finish once drying intervals have been factored in. However, the results speak for themselves.

After seven months, Silic One has performed the best of all our group, with no signs of weed or shell growth and the least amount of surface slime. It also wiped off exceptionally easily. An impressive result for a biocide-free antifouling paint.

Because it has a recommended lifespan of two years before topping up with one fresh coat of Silic One, the high initial application cost is offset over time.

Its six-year annualised cost comes in lower than all other products on test except Hempel Tiger Xtra 7100 and Coppercoat if you exclude the cost of shotblasting.

Buy it now from Amazon

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Impressive value, but needs applying every year

Hempel Tiger Xtra 7100

Editor’s choice – best value

Type: Eroding annual biocide
Preparation: Hempel Underwater Primer (2 coats)
Initial cost: £298
Annualised cost: £167

While it might not be the most technically sophisticated formulation out there, for many boat owners Tiger Xtra has become a go-to product – a reliable staple and a firm favourite on the winter maintenance list for the past 20 or 30 years.

With one of the highest m2/ litre coverage rates of anything tested here, applying Tiger Xtra will soon have you making decent progress across the hull in a relatively short space of time. The prospect of coating even larger than average-size hulls needn’t be as daunting, or as expensive, as you might have first imagined.

The question is, does it work? And the answer to that question is yes, in a similar way the other fast-eroding formulations have benefited from the vigorous, weekly use that Raymariner has been subject to these past seven months.

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BEFORE (left): Easy to apply and leaves a smooth finish. AFTER (right): A similar amount of slime, but easier to wipe off than others

Self-polishing mechanisms need movement of water across the hull and Tiger Xtra has proved its formulation is still a worthy contender even after all this time. Slime was also a little easier to release from this coating, compared to some of the others.

The only unknown quantity is whether this more thinly spread coating would continue to deliver over a longer length of time, especially in warmer waters with higher fouling.

Hopefully, we’ll get a chance to monitor this on our test panel but on this showing it represents good value for money compared to its similar performing annual rivals.

Buy it now from Amazon

Easy to apply, average performance

International Ultra 300

Type: Hard annual biocide antifoul
Preparation: Primacon (1 coat)
Initial cost: £446
Annualised cost: £326

Prior to this test Raymariner had been coated with International’s Micron 350. When it was lifted in June 2021 in preparation for our test patches, the hull had appeared in remarkably clean order.

This time around we opted for Ultra 300 Hard, as the hard and slow-eroding formulation lends itself well to fast or regularly used motorboats. It would also be suitable for yachts on drying moorings that need a harder antifouling paint.

After applying just one recommended coat of primer, we applied two, good coats of Ultra 300 in a straightforward and fuss-free way, making life so much easier for the DIY applicator. Job done.

BEFORE (left): Another easy to apply coating that leaves a smooth finish. AFTER (right): The usual layer of slime but a bit harder to shift than some

The results have been good, but marginally less impressive than Micron 350 looked back in June, although that could be down to seasonal differences in water temperatures and fouling growth.

The Ultra was sheathed in a film of slime, thicker near the waterline, as expected. And when we tried to wipe the slime away with a damp microfibre towel, it showed quite a lot of resistance, suggesting it had taken hold quite firmly – though nothing that a jet-wash wouldn’t shift, and with no long beards of weed, or signs of shell growth.

At an annual cost of around £326 for a typical 36ft boat (£446 if you include the cost of a primer coat), it’s a solid, easy to apply performer.

Buy it now from Amazon

Slime is easy to shift, but this antifoul is pricier than most

Jotun NonStop II

Type; Eroding annual biocide
Preparation: Jotun Megacote Epoxy (4 coats), Megasealer Epoxy Tie-Coat (1 coat)
Initial cost: £463
Annualised cost: £355

As we’d stripped Raymariner’s hull back to the bare gelcoat Jotun decided to send us their epoxy primer, tie-coat and combined anti-osmosis system, prior to applying the two final coats of Jotun NonStop II.

While this belt and braces approach makes sense on a brand new hull, we felt for the purpose of our price comparison table it would be fairer to use the costs of Jotun Vinyl Sealer – a straightforward one-component product that we have been assured can also be applied to bare gelcoat.

Jotun Vinyl Sealer is ideal for those looking to antifoul an already treated hull in good condition and is a readily available product the DIY user would be more inclined to buy.

BEFORE (left): Blue is one of several colours available in this range. AFTER (right): A decent result comparable with other more traditional antifoulings

If the existing coating is a known Jotun product and in good order, with no damage or signs of flaking, Jotun NonStop II can be applied without even needing a primer.

The results in January showed good overall performance, broadly similar to the other copper-biocide products, with no significant weed or shell growth to talk about but a thickish layer of slime that shifted quite easily when given a wipe with the towel.

Even using the basic vinyl primer for the initial application, the annualised cost still makes this one of the pricier options so it will be interesting to see if it lasts longer than the cheaper options over time.

Buy it now on Amazon

Solid performer, but needs regular stirring

Seajet 033 Shogun

Type: Eroding annual biocide
Preparation: Seajet 015 Primer (2 coats)
Initial cost: £486
Annualised cost: £289

When we heard about a new non-biocide alternative from Seajet, it made sense to compare it alongside Seajet Shogun, its best-selling, copper-based formulation.

Backed by the commercial resource of Chugoku Marine Paint, Seajet first appeared in the UK about 20 years ago and carved a niche for technical-quality antifouling paints.

Despite the fact Seajet products are often found on the lower reaches of chandlery store shelves, Shogun is a reliable performer and a product that many boat owners have become fiercely loyal to.

BEFORE (left): Needs a good stir but paint goes on evenly. AFTER (right): Another solid performer with no shell or weed growth

One thing we found when applying Shogun is the copper and zinc volume solids sink to the bottom and to achieve a homogeneous consistency, it’s important to ensure a good 5-10 minutes of continuous stirring with a wide blade stirring stick, not just the screwdriver you used to prise the lid off.

The vapour given off made us glad we were outside in the fresh air but the coating itself goes on in a thick and consistent way.

Largely in-keeping with the other self-polishing brands on test, close inspection returned a good, solid performance, with no signs of shell growth, or significant plant or weed growth to talk about. The extra coat of primer added a bit to the initial cost of application but in subsequent years the cost comes down considerably.

Buy it now on Amazon

Boasts a 3-year lifespan, but we did see some fouling migration

Seajet Bioclean Eco

Type: Biocide-free medium term antifoul
Preparation: Seajet 117 Multipurpose Epoxy Primer (3 coats), Seajet Bioclean Tie-Coat (2 coats)
Initial cost: £1,011
Annualised cost: £268

Seajet Bioclean Eco has a rubbery-like finish that fouling finds difficult to adhere to. It is a seven-coat full system on bare gelcoat but can be applied on top of existing antifouling in good condition, with two coats of tie-coat, followed by two coats of Bioclean Eco.

Dry weather meant we made steady progress, first with three coats of epoxy primer, then the coloured tie-coat stage before two good coats of Bioclean Eco, a thick and transparent, paste-like substance. On Seajet’s advice we used a clean mohair roller head to achieve the required film thicknesses.

BEFORE (left): Shiny silicone- based foul-release system is available in several colours. AFTER (right): Almost no fouling bar some migration of growth from the untreated dividing strip

When lifted, the test strip was admirably clean and foul-free but there were some patches of fouling that appeared to have migrated across from the untreated dividing line separating this test patch from the neighbouring one rather than starting life on the surface of Bioclean Eco itself.

The amount of slime was less than on the biocide products and the wet microfibre towel test showed that resistance to removal was also less.

Seajet expects it to last for at least three years after which another tie coat and top coats are likely to be needed, although as this a new product the recommended routine isn’t yet fully established. The PBO Project Boat, a Maxi 84, has been coated with Seajet Bioclean Eco so we’ll be able to update you in due course.

Buy it now on seajetpaint.com

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Full price comparison – click to enlarge

Verdict: Which is the best antifouling paint?

Almost all of the coatings did an effective job of keeping fouling at bay but there were some notable differences between them, not just in terms of performance but also cost, application time and environmental credentials.

Coverage rate per litre was different according to the product. Coppercoat do not state a coverage rate but prefer to calculate the amount you need based on your boat type and length. All the figures on the table were based on a 36ft motorboat hull, of 34m2 surface area.

The silicone based biocide-free alternatives performed very well, especially Hempel’s Silic One. If you’re prepared to put up with the higher initial cost and time taken to apply these products for the first time, they really do deliver on their promise and the price differential reduces over time.

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Antifouling stripes were applied to the hull of Raymarine’s electronics test bed vessel Raymariner, a Hardy Commodore 42, in June 2021

They won’t suit every boat, however, as silicone can dry out if left unsubmerged for long periods and may start to wear through if kept on a dry-stack or drying-mooring, but for the majority of boats they look like an effective alternative to copper-based antifouling paints.

Coppercoat’s tough finish is fine to use on a drying mooring or dry stack and has the next best eco-credentials of our group. It performed almost as well as the traditional annual antifouling paints but should last for 10 years or more with minimal annual upkeep.

It does have to be applied to bare gelcoat, though, which ramps up the initial cost. On our fictional 36ft boat we calculated the break even point at about six years but this would come down substantially if you included the annual labour costs or were applying it to a brand new boat that didn’t need stripping.

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Adam Fiander coated the hull of Raymariner and a test board for immersion in a marina

There was little to choose between the traditional biocide antifouls, which supports the view that if you prepare the surface and apply it properly most antifouling paints will do a decent job of protecting your boat, at least over the course of a single season in UK waters.

Hempel’s budget offering, Tiger Xtra, is still providing incredibly good value protection after all these years, and Seajet Shogun, International Ultra 300 and Jotun NonStop II have proved their worth with solid, reliable protection that was impossible to split during the course of our initial test period.

We’ll continue to monitor the performance of our static test panel to see if this is still the case over the coming season and beyond. In the meantime, thanks to Raymarine for allowing us to redecorate Raymariner’s hull and we’ll report back again this time next year.

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