In June 2021 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.

18-month update

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. The boat was repainted with fresh antifoul after our initial test ended, but the static panel allowed us to see how the coatings fared 18 months since the test began.

It’s important to remember that a boat would not normally sit idle and uncleaned for that length of time, making the test more challenging for all our products but especially the ‘foul-release’ coatings which rely on water movement to help shift any fouling.

Now that the boat-based test has reached its conclusion, the static panel provided a valuable cross-check for the longer term performance of the products based on a visual assessment of the stripes, a finger swipe to see how easily any fouling came away, and a sponge wipe to check if the coating itself came away too.

Like the boat, our static test panel was immersed in a Portsmouth marina location in June 2021. Apart from the effect of the tide sweeping across it, the panel has remained in situ there, fully immersed at all times for the last 18 months.

As you can see from the pictures, the coatings have, by and large, performed extremely well. Apart from silty mud covering the test stripes, there are very few signs of serious fouling having taken hold on any of the coated sections.

Even green slime – highly prevalent when Raymariner was lifted a year ago – appears to have taken a back seat in this case, perhaps because the panel has been lying in a shaded area for most of the time. Proof of how well the coatings have performed can be seen by the growth of weed and up to 10cm long sea-squirts on untreated sections.

Quick links

• Best value: Hempel Tiger Xtra 7100 – Buy it now from Amazon
• Best in test: Hempel Silic One – Buy it now from Amazon

High on slime

2021’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 2022. 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.

8 of the best antifouling paints tested

Coppercoat

Type: Epoxy based 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.

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.

18-month update

Even though Coppercoat recommends an annual scrub or pressure wash to remove any surface growth, it still seems to be performing well after 18 months untouched. There was no significant fouling on the exposed copper surface, which has now adopted its characteristic blue/green colour, and minimal resistance from the swipe tests, suggesting any surface growth would fall away on a regularly used hull.

As expected of a tough epoxy based product there was no sign of the coating coming away on the sponge. Coppercoat’s claims of it being more environmentally friendly than erodible coatings.

Buy it now from coppercoat.com

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Hempel Silic One

Editor’s choice – best in test

Type: Non-biocide, silicone based foul-release coating
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.

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.

18-month update

We had expected foul-release coatings to struggle on a static panel without any movement through the water to shift surface fouling. However, the majority of the stripe stayed remarkably clean and any slime was easily swept aside with the swipe test.

Some isolated growth can be seen at the top of the strip but this could have been caused by migration of fouling from the untreated section in-between this and the Seajet Bioclean Eco (the other products were separated by a strip of white Trilux antifouling). So far there are no signs of any surface deterioration.

Buy it now from Amazon

Hempel Tiger Xtra 7100

Editor’s choice – best value

Type: Soft eroding biocide antifouling
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.

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.

18-month update

We were pleased to see how well the cheapest of our traditional antifouling coatings coped on the boat and the results from the panel did nothing to change this view. Our initial inspection showed no more fouling growth on this than any of the more expensive products and the finger swipe test easily shifted anything that was there.

Some of the coating surface colour did transfer onto the sponge, which is normal for a soft eroding coating, but over time it might start to wear through on a fast, regularly used boat.

Buy it now from Amazon

International Ultra 300

Type: Hard eroding biocide antifouling
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.

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.

18-month update

Although this is a traditional copper-based antifouling, it is a slow eroding hard coating designed for faster planing craft with increased water friction that might wear through softer products.

This didn’t affect its performance on our static test panel with little fouling growth over the 18 months and no sign of it starting to lose its antifouling properties. The swipe test suggests any fouling would fall away on a moving hull used regularly, while the sponge test showed only slight signs of the coating releasing itself.

Buy it now from Amazon

Jotun NonStop II

Type: Soft eroding biocide antifouling
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.

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.

18-month update

This premium priced self-polishing coating uses ion exchange technology to ensure a steady release of biocides throughout the year, even when the boat is not being regularly used. While it performed well it wasn’t noticeably better than some of its cheaper competitors.

However, it did have the highest degree of coating surface being released onto the sponge suggesting it was eroding consistently even without regular boat movement – a good thing as long as it has been applied in sufficient quantity.

Buy it now on Amazon

Seajet 033 Shogun

Type: Soft eroding biocide antifouling
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.

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.

18-month update

Sold as a premium self-polishing annual treatment for boats capable of up to 40 knots in areas of high fouling growth, this antifouling treatment still seemed to be performing well after 18 months on our static panel.

There was minimal surface growth and only a light smattering of slime. As expected, a certain amount of blue coating did release onto the sponge when the panel was wiped, suggesting it will eventually wear through and reminding us not to skimp when applying this type of erodible coating.

Buy it now on Amazon

Seajet Bioclean Eco

Type: Non-biocide, silicone based foul-release coating
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.

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.

18-month update

As with our other foul-release coating, this performed far better than expected on our static panel, suggesting it would still provide good protection on a less frequently used boat.

Fouling clearly finds it hard to adhere to its slippery, rubber-like coating even in a static situation like this and the swipe test suggests it would perform even better on a regularly used boat.

There were signs of isolated growth at the top and bottom but this could have been caused by migration of fouling from the untreated section between the two silicone-based coatings.

Buy it now on seajetpaint.com

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.

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.

18-month update: N/A

Buy it now from ceramicpro.co.uk

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.

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.

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.

18-month update conclusions

While the results of the long-term panel test have helped to back up the findings from our original boat-based test, there was not a big enough difference between the performance of the various different coatings to justify changing any of our original boat-based star ratings.

All seven products provided a good degree of antifoul protection when compared with the growth on even the smallest untreated sections of the panel. The extra fuel cost in dragging a carpet of unsightly fouling like this on the underside of your hull does not bear thinking about.

Our tests prove that even a moderately priced traditional copper biocide can provide all the short-term protection you need. But be prepared to keep an eye on soft, self-polishing and erodible coatings such as Seajet Shogun, Hempel Tiger Xtra or Jotun NonStop 2, because they will need topping up each year or re-applying in full every two seasons.

The fact that our test panel wasn’t moving may have helped extend the life of these products. Hard coatings such as Coppercoat or International Ultra 300 lend themselves to the extra friction from faster hulls but may need occasional scrubbing to maintain their performance when the surface layer starts to lose its potency.

They are designed to withstand being scrubbed and should not get damaged if you keep your boat on a trailer or in a dry-stack. However, on the basis of this long-term panel test, they seemed to maintain their performance for the full 18 months without any intervention and in the case of Coppercoat should carry on doing so for years to come.

If you’re willing to invest the extra time and cost of applying a silicone-based foul release coating, either of the two that we tested will, on the evidence of this test, do a very good job for you, even if your boat isn’t used that regularly.

The fact that they do this without the use of biocides can only be a good thing for the long-term health of our rivers and seas. You do need to follow the instructions carefully, because each of the three stages of primer, tie-coat and top-coat need correct application for the coating to perform well as a whole.

However, once applied, they should last for several years but tread cautiously with your annual maintenance routines, because a powerful pressure-washer can dislodge the layers if held too close.

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.

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 antifouling paints, so manufacturers are coming up with a number of biocide-free alternatives. Silicone based formulations – such as Seajet Bioclean, which we used when applying antifoul to the PBO Project Boat – 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.

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?

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