How Hempel's Silic One silicone antifouling performed over two years on my 27ft boat

Stuart Guy shares the results of how Hempel’s hydro gel fouling-release system has performed on his Hunter Pilot 27 over two years

the bottom of a yacht painted with Silic One antifouling

The finish before launch: epoxy primer tie coat; two coasts of Silic One. Credit: Stuart Guy Credit: Stuart Guy

Hempel Silic One antifouling: PBO reader tested

The drying mooring where I keep my boat is a challenge for any antifouling system, as it needs to be able to cope with the constant friction and abrasion caused by my Hunter Pilot 27 regularly contacting a muddy seabed, writes Stuart Guy.

In 2023, I decided to try biocide-free with the Silic One Fouling Release antifoul.

The underneath of a yacht painted with Hempel Silic One

End of season, first year – the hull was easily wiped down with a sponge to be as clean as before. Credit: Stuart Guy

I was the first member of the Hunter Association to try it and was surprised when I asked around how little was known about its use for small boats.

So I decided to record my findings about going biocide-free. If it worked, I hoped to encourage other boat owners to avoid using copper as it leaches into our creeks and harbours.

What is Silic One?

Silicone marine coatings have been around for decades and are used on many cargo vessels, but have only recently been marketed to the recreational sailor.

In 2023, when I decided to give it a go, it cost about twice as much as premium ablative antifouling biocide, but once applied, only one coat is required every two years, and there’s no rubbing down to prepare the surface.

Hempel’s Silic One can be applied to any sound antifouling substrate, but Stuart chose to remove all the flaking antifoul and start again. Credit: Stuart Guy

The coating is effectively inert and safe to use on sensitive waterways. Hempel’s Silic One can be applied to any sound antifouling substrate, but I chose to remove the flaking old coat to start again.

What is Silic One like to apply?

The foundation was done in one day, overcoating the epoxy light primer after four hours with a maximum of eight hours at 10°C.

It’s very easy to apply with a 4in short hair roller. The actual silicone paint must go on within 16 to 48 hours, so I did it the next day.

Subsequent coats must be within 48 hours or it will require a wash down with Hempel Pre-Clean or equivalent industrial detergent, rinse and dry (two coats are recommended for the first application only).

The thick silicone paint goes on like standard antifouling. A large 9in short hair roller was quickest, but a 4in roller was more precise.

I used 2.25lt for the first coat. It levelled up imperfections well.

What to expect

When the coating dries, it feels just like silicone sealant, rubbery to the touch. I was concerned about its resistance to knocks, so I did a test piece and attacked it with a screwdriver tip – which did cause damage as you might expect.

The tie coat is very well bonded to the epoxy primer, however.

When I rubbed the silicone surface with the side of the screwdriver, it did not mark it, so it is abrasion-resistant.

A man touching Silic One antifouling on his yacht

It looks the same, but its rubbery touch feels quite different! Credit: Stuart Guy

Sailors should not expect the total release of fouling on a slow-moving yacht, but after a whole season’s use, it continues to perform well for me.

The great virtue is that the surface can be cleaned easily with a sponge and does not cover the creek with blue biocide, and that makes me and the marine life happy.

I’m fortunate that my twin-keel yacht can easily dry out mid-season so I can sponge off any crustaceans and slime that are not removed by the hull’s motion.

If you need to employ a diver, it should be a quick job.

The silicone coating does not shed into the environment during normal use, unlike ablative copper-based systems, and will never need rubbing down to refresh it.

Cargo ships only go into dry dock every two to three years for a refresh and have recorded consistent fuel and efficiency savings. I’m hoping for this too.

I also applied several coats of PTEF hull polish on the splash zone twice a year to help release fouling from the topsides.

How did Silic One perform?

The photograph (below) was taken after 10 weeks in the water, without even a wipe down.

The bottom of a yacht showing the propeller

Silic One after 10 weeks on a half-tide mooring and a couple of trips away, anchored in mud. Credit: Stuart Guy

Compare my hull’s condition to the boat next to me, launched at the same time with the standard International Cruiser antifouling (below).

Control hull with International Cruiser launched at the same time. Credit: Stuart Guy

The ‘tide mark’ of silt that usually adheres to my hull as the tide recedes is not present, which indicates that the non-stick surface does reduce adhesion even on slow-sailing boats, despite this system being designed for commercial vessels reaching 15 knots.

In addition to the drying mooring, I have anchored in the mud, and the Silic One has not rubbed off the keels.

After the first year’s use in mid-October, the results were small barnacles, no slime, splashed-up mud on keels, but no weed.

Some algae at the waterline was tricky to remove, but the hull was easily wiped down to be as clean as when first applied.

a few barnacles growing on the hull of a boat painted with Silic One

A light touch and the barnacles fall off due to Silic One’s fouling release properties – use a sponge or gloves. Credit: Stuart Guy

For my mooring, the fouling release has worked as claimed so far. But you must be prepared to wipe down with a sponge twice a season to dislodge stubborn barnacles.

My twin keel hull is ideal for drying out on the hard, so this suits me. The wipe down requires very little effort.

The initial application is an easy DIY job and can be applied to existing antifouled hulls.

Hempel recommends just one coat every two years. On this basis, the cost over 10 years is similar to other systems.

Two years on, during the first lift out, I was able to remove the remains of weed and slime with a brush and hose without any biocide run-off into the creek.

The Silic One has been scratched off in places from knocks aground or by the anchor chain. Credit: Stuart Guy

The hull was clean and smooth when I finished.

Some of the top coat had scratched off from contact with obstructions, but it is minor.

Any damage is easily touched up with a single top coat.

As with all antifouling systems, it is best not to expect 100% fouling-free – then you won’t be disappointed!

Material used for a Hunter Pilot 27

3 x tins 0.75lt Hempel Light epoxy primer n 2 x tins 0.75lt Hempel tie coat (Three tins recommended but did not use one tin)
2.25lt Silic One for coat one (this was 1.5x as much because it went on rather thick)
1.25lt Silic One for coat two (I used a small roller in 12°C and it covered the entire hull OK)
Total used for two coats Silic One 3.5lt as recommended every 2 years
Total cost: approximately £289.75 including the primer
Watch Stuart’s YouTube video at youtu.be/IRSzmEFII1Q

Expert view on biocide-free antifouling

RYA Green Blue campaigns manager, Kate Fortnam, comments:

Most biocides in antifouling enter the marine environment through leaching; however, concentrated amounts can be introduced during paint application through drips and spills, as well as during removal by water blasting or mechanical scraping, leading to deposits on land and in waterways.

Biocide-free antifoul coatings are now available to support the boating community in protecting our waters, wildlife and habitats:

Foul-release coatings like silicone – slippery not poisonous.
Ultrasonication that uses ultrasound waves to deter biofouling on the hull.
Biomimetic coatings mimic the surface of aquatic species, such as shark that have little algae growth.

Find advice on environmental best practice for antifoul coatings work at The Green Blue.

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