Boats that are kept afloat can very quickly become a home for small marine organisms such as barnacles, weed and slime. Applying an antifouling paint to your hull is necessary to protect it from these micro-organisms, as a fouled hull can cause problems and will slow down a boat’s maximum speed considerably if left unchecked.

There has been much controversy over the years about antifouling products due to their detrimental effects on marine life, especially in marinas and crowded anchorages in estuaries. The big challenge for the paint manufacturers is to develop products that will keep hulls free of foul without harming the environment.

There are two main types of antifouling paint used for leisure boats, normally referred to as hard and eroding. Both contain biocides that kill and deter fouling organisms but they work in different ways and are designed for different types of boat. The basis of most biocides found in antifouling are copper (Cu) and cuprous oxide (CuO). These are effective at deterring the growth of molluscs, larvae and some types of weed but there needs to be high concentrations of copper in the paint for them to work. To be completely effective, some antifouling also contains zinc based biocides or organic algaecides.

When choosing antifouling for your boat, it is advisable to talk to your local chandleries as they should be able to tell you what antifouling is best for your type of boat, its location and the environment. It is important to know the type of antifouling currently on your boat, as not all types of antifouling are compatible with each other.

Hard antifouling

Hard antifouling slowly releases biocide which prevents foul from settling on the hull. The biocide can last a whole year and if several layers are applied, even longer. However, the leaching rate reduces over time and the paint loses its efficiency. This type of paint has a hard finish, which enables it to be scrubbed or wet sanded through the season to keep the bottom in good condition.

Hard antifouling is popular with boats where maximum performance is required – racing yachts and fast powerboats for example. It is also used for boats kept in fresh water as the alternative, eroding antifouling, is designed to be used in salt water and does not perform as well in fresh water.

There are some types of hard antifouling with a very high copper content, where tiny particles of copper are suspended in epoxy resin. Several layers of this copper resin have to be applied very carefully to a pristine hull. This process is normally done by a small professional team under controlled conditions. The final coat is sanded, leaving a layer of copper oxide that is effective, very hard wearing and can last up to 10 years or so. Copper resins are expensive to buy and apply in the first place, but after a few years they become a viable option as there is very little maintenance required.

Eroding antifouling

Eroding antifouling is also known as soft antifouling and like hard antifouling slowly releases biocide. The big difference between the two is that the paint itself erodes into salt water, leaving very little residue on the hull itself. This is ideal in many ways for the cruising boat owner as it reduces the build up of successive layers of antifouling and makes maintenance much easier. However, this is not so ideal for those who want to keep their boat’s bottom in pristine condition through the boating season as scrubbing or sanding it smooth takes off the paint.

Therefore, eroding antifouling is more widely used for cruising yachts and displacement motorboats where speed is not the absolute priority.

Non-toxic antifouling

Recent developments in antifouling technology have concentrated on finding non-toxic solutions which are environmentally safe. There have been some significant breakthroughs in recent times.    

There are several silicon based products available that form a very slippery surface which prevents micro-organisms from gripping onto the hull. While these developments have generally been well received by the leisure marine community, they perform best on hulls that regularly move through the water at speeds of 10 knots or more. A great idea for powerboats but not so excellent for most sailing yachts that rarely, if ever, exceed 10 knots through the water.

Another option to consider is electronic antifouling, which uses ultrasound technology to deter fouling organisms. These systems are easy to install and can be undertaken by competent DIY boat owners. You do have to swallow hard when it comes to the price but perhaps in the future these will become common place and more affordable – I hope so.