The best antifouling for your boat.

Confused about which antifouling to buy? In 2017 (which now seems a long time ago) Practical Boat Owner carried out an antifouling test and went to great lengths to help answer this question but we think it was missing some vital hints and tips.

The Captain Watts antifouling guide looks at the test results but also advises on the right antifouling for your boat type in 2021 when lots has changed, especially with regard to International Antifouling. Some of the products in the only real test there has been were superceeded in 2019 and since then we are working on customer feedback to keep you updated.

Which type of antifouling is best for my boat, hard or eroding?

Eroding, or self-polishing antifouling (often referred to as soft antifouling) works by slowly eroding over the course of the year or sailing season, to keep your hull clean. A quick jet wash at the end of the season should leave it spotless and ready for a fresh coat.


Generally, this is suggested for boats with a speed of up to 25-30 knots, which equals the vast majority of sailing boats. The PBO test was specifically aimed at this market (it is after all mainly a sailing magazine) and the results were relatively consistent across UK waters. 

The leading light of the Practical Boat Owner antifouling test was Seajet Shogun 033 which led in at least 8 of the 13 tested locations around the UK. There was one clear fail in Scotland, whatever is in the water in Inverkip seems to create more slime that the leading players can handle! However, Seajet Shogun 033 Antifouling was a clear winner in the test, which was perhaps the most comprehensive undertaken by a sailing magazine.

What if you want to spend less?

Antifouling is hardly a glamorous investment and one that spends most of its time hidden below the waterline. One of the brand name products consistently up there in the top 5 was International Cruiser Uno, this has now been replaced by International Cruiser 250. Cruiser 250 has, to our understanding some of the Cruiser Uno ingredients removed, but, as it is too early to see results we don’t know for sure if this will still work as well. The good news is it is available in varied colours and a 3 litre tin. It remains a one-year antifouling.

If you want to spend a bit more, you could consider International’s Micron 350.We recommend this for those who previously used  Micron Extra or Micron Extra 2 on their hull, so if you are worried about compatibility Micron 350 it is sensible antifouling to use.

There is more to the to Micron 350 story though, this is not a simple remix with additives removed but a totally new formula, designed for 2 seasons and works in a different way to the old Micron or  new Cruiser 250. It has much better control over the release and no longer relies on a constant flow of water, all thanks to the use of a self-polishing copolymer binder (see the product for more details). Although more expensive this may well be the better International antifouling for yachts in 2021.

If you are regularly exceeding 25 knots you will likely have a planing boat or a racing yacht (serious racing!), in which case you may need to consider a hard antifouling. PBO’s tests did not include these but it is worth reading the small print as Seajet says that the Shogun 033 is okay for use up to 40 knots.

Do you need speed or race?

Hard antifouling does not erode or self-polish, hence the reason it copes better with high speed. If you are in a mud berth or low fouling area we would suggest Seajet 037 Coastal, which is a good all-round product, rated up to 70 knots and only £59.95 for 2.5 litres. 

For heavier fouling areas, we recommend International Ultra 300 or Hemple Hard Racing antifouling as great options for racing yachts, as they can be burnished. They are a premium products but friction is bad news when looking for every little help to beat the competition and these products help to make your boat more slippery compared to standard cruising options. 

For those antifouling an aluminium hull, first and foremost, DO NOT use any of the above-mentioned products on aluminium, or any other copper-based coatings. For aluminium hulls, we recommend International Trilux, which is specifically designed for the task. This is also the most appropriate antifouling for your prop shaft, prop (if you choose to coat it) and leg. 

 A Simple Guide to Common Types of Antifoul

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Preparation & Application

As with all painting, preparation is the key, but this is not varnish, so you don't need to go overboard. Compatibility is a consideration and manufacturers all have a primer/barrier coat available in the same range. Check first though, as some are perfectly compatible. If you are at all unsure, speak to Dave at Captain Watts in Plymouth who is ready to help.

It probably goes without saying, but give the hull a good jet wash and scrub before you do anything, for which we would suggest using the Shurhold brown pad. Finally, and if really needed, a wet sand. Do not sand with normal dry paper!

The number of coats required varies from product to product. Cruiser Uno is sold as a one coat for low fouling areas, and many others say the same thing, although after a season or two, you will know if you need more than one coat for the amount of time you spend on the water and the type of fouling you face. Many of the big names recommend three coats which will last two seasons. Obviously, it costs more to start with but saves preparation before the start of the next season. 

The Captain Watts Antifouling guide has been prepared based on the information available for manufacturers at the time. There is no substitute for reading the tin and checking with a real human being. We have data sheets available for all the products we sell and will happily help you choose the best antifouling for your boat.

Notes. In 2018 the EU rules and regulations on the makeup of antifouling were updated. International had to change their key Cruiser Uno and Micron Extra Antifouling, it is too early to tell the effect of the new formula but anecdotal evidence appears to suggest the Micron 350 is working well. Unfortunately the 2020 season has been less than useful as many vessels were sat on their moorings for longer than normal and then used more than normal!