Before you apply antifouling (see How to prepare and apply antifouling), it pays to understand what paint you should use and understand how it works.
There are many tasks that have become easier and more cost effective over time thanks to improvements in technology. However, that’s not true of antifouling paints. Even though most manufacturers are investing plenty of research in improved formulations, the problem is that the ultimate protection for the bottom of your boat is incompatible with the health of the marine environment as a whole. Put simply, keeping too many boats in one location over a long period of time means that high-strength antifouling products not only keep the bottom of a boat clean, but they also become responsible for slowly wiping out marine life in a wider area.
Get to know your biocides
While the first high-profile change was in 1987 when the use of tri-butyl tin (commonly known as TBT) was banned Europe-wide on boats under 25 metres, the noose of legislation has continued to slowly tighten.
In order to choose the best antifouling product for your boat, it’s important to have an appreciation of the types of biocide that are typically used in antifouling paints. The most common is copper oxide, which copes well with keeping weed and animal fouling at bay. However, it’s much less effective at preventing slime, which is why more expensive brands also include various organic biocides.
Below is an outline of what antifouling paint you might want to choose for different types of boat and patterns of use. It’s important to recognise that the optimum type changes not just for different styles of boats, but also how often the boat is used and the purpose for which the vessel is used.
1. 33ft sailing cruiser
Boat used: minimum three weekends a month May to September
This boat is one of the easier ones to protect, so a mid-priced eroding product such as International Cruiser Uno or Hempel Cruising Performer will have a reasonable chance of doing the job with acceptable efficiency. There are a number of reasons for this: firstly, if slime forms towards the end of the season, then on a cruising sailboat it’s critical to neither performance nor fuel economy. Secondly, the very fact that the boat is used regularly will help the eroding antifouling paint to do its job, thereby minimising the build up of slime in the first place. Thirdly the relatively short (five month) season means that prolonged protection is not required.
2. 36ft racing yacht
Boat use: One or two cross Channel or similar races per month, over a seven month season.
This is a much tougher scenario, as the boat is used less frequently over a longer season, which gives more time for slime to build up between outings. In addition, any slime that does form will quickly take the edge of the boat’s performance and while losing 0.2 knots won’t matter much to a cruising yacht, for a racing boat it can make a half hour difference on a 100-mile race.
For this boat a quality hard racing antifouling paint such as Nautix A4, Hempel Hard Racing or Flag Performance Extra will give excellent short term protection and allow the boat to be lifted to clean the hull before your most important races.
3. 42ft long distance cruiser
Boat use: continuous cruising in warm waters for 10 months per year.
If you’re in a position to clean the bottom of the hull from the water, then a product such as Coppercoat would be worth considering and may eventually repay its high up-front cost several times over. While this isn’t as good at preventing slime as conventional antifouling paints with a relatively high organic biocide content, particularly for boats that don’t move much. However, if you’re regularly on the move and tend to anchor and swim in the kind of places where it’s easy to give the bottom of the boat a quick wipe periodically this may be a good choice.
Alternatively, a high-performance eroding antifoul such as International Micron Extra 2 or Hempel’s Ocean Performer will keep marine life at bay for longer than lesser products.
4. 40ft planing motor yacht with 23-knot cruising speed
Use: one weekend per month, plus a two-week summer 400 mile cruise
Just as the racing yacht needs to avoid the build up of slime, the same is true of fast power boats. Even a small amount of growth will increase the amount of power needed to get on the plane, significantly increasing friction, and therefore fuel consumption, at speed.
Most eroding antifouling paints are not recommended for speeds above 17 knots, so this factor is likely to limit you to the hard racing types – as with racing yachts it’s worth choosing a top quality product as the relatively modest extra cost will easily be covered by fuel savings. In addition, you’ll want the hull and propellers to be as clean as possible for your summer trip, so schedule a lift out and pressure wash as close to the start of this as you can.
5. 25ft RIB or sportscruiser
Use: Bank holiday and occasional long weekends from Easter to September, plus a handful of day trips during a two week summer holiday.
For a boat like this the arguments against even bothering with antifouling get stronger each year. Given that it’s next to impossible to keep the bottom of a boat that’s only occasionally used clean, and this type of boat is very sensitive to any layer of slime, for most owners it would be better to admit defeat. Instead of keeping the boat afloat, book a slot in a dry stack.
This means you won’t need to pay for moorings, or for annual antifouling, yet the bottom will always be clean when you want to use the boat. In addition, given that most drystack facilities provide a degree of protection from the elements, it will also be dry and clean each time you want to go out.
For more information and advice on antifouling paint, see: How to prepare and apply antifouling or How to choose antifouling paint.