Antifouling Answers

What is the best Antifouling paint?

This really depends on what you are applying it to and the amount of use the vessel will get. It is not just a case of what is the strongest, what lasts the longest and rarely what the antifouling costs! The easiest way to explain is to look at the types of antifouling and their intended uses.

There are two main categories, Commercial and Leisure antifouling. This is a touchy subject among leisure users who now find it difficult to obtain commercial products. However, while they may be stronger, products that are designed to be used on ocean going ships which have service intervals of 3-5 years may not be the best for leisure craft. This is especially true of coastal vessels that may spend a lot of time in the marina. If you would like to read more on the commercial vs leisure antifouling debate click here.

What does antifouling paint do?

Antifouling paint makes the underwater areas of your boat unattractive to marine life especially crustaceans such as barnacles and shellfish. These organisms attach themselves to the hull and cause significant drag resulting in a loss of speed and fuel efficiency. Preventing fouling is accomplished by introducing a biocide (in most cases variants of copper) to the surface. They do not necessarily prevent plant growth so even a well antifouled boat may still have slime or some growth but as these organisms require light this is usually only near the surface. By their very nature antifoulings also pollute so it important that they are used responsibly and it is worth spending the time to find the best one for you which has the minimum environmental impact.

Types of antifouling paint

There are two main types of antifouling:

Self-Polishing antifouling

This is probably the most common form of antifouling. They work by slowly eroding away in seawater releasing biocides that prevent marine growth. The binders determine how fast this process takes and as the paint film tends to become smoother over time, they are known as self-polishing. You can often see the process of erosion when you wipe the hull you’ll see a small cloud of product washing away. There are many variations in the speed of boats, the amount of time they are being used and the water conditions (temperatures, salinity etc) and it is for this is the reason one antifouling will work well on one boat and not as well on another. The same product may even work well one season and not another. The manufactures try to find a balance that will give the best results for the most common situations but there are no self-polishing antifouls that work flawlessly in every situation for every boat. If you time it right there should be little antifouling left when you come to take you boat out of the water again meaning less preparation to apply fresh antifouling.

If you have a boat moored and used in freshwater these antifoulings are not suitable as they are designed to erode in saltwater.

Hard antifoulings

Hard antifoulings work by leaching biocide from the surface of the coating, they do not erode away and over time the leaching rate is gradually reduced until there is no biocide left. These antifoulings are more predictable but once the biocide is depleted they need to be removed before applying fresh antifoul. As they are a hard coating these products can be sanded to a polished finish prior to any racing.

Hard antifouling are especially suitable for fast boats as self-polishing or eroding antifoulings would simply wear away too quickly. They are also more suitable for freshwater as they do not rely on salt water to release more biocide.

How long does antifouling last?

Hard antifoulings can be considered quite predictable depending on how many times they are sanded to increase speed.  A hard antifouling will usually last a season but for leisure users this is ok as this type of vessel will be lifted out more frequently. For racing yachts and speedboats that regularly have their hulls scrubbed this type of antifouling is necessary as constant scrubbing will remove all self-polishing antifouling very quickly. There is no need to apply multiple coats of hard antifouling as the top coat will not erode away to reveal the underlying coat with fresh biocide.

For self-polishing antifouling the question of how long it will last is much more difficult to predict. However, as the thickness of the coating is important it can be generally said that the more you apply the longer it will last. In ideal conditions each coat should last one season. However, simply brushing the hull with your hand will remove a layer of self-polishing antifouling (this does not necessarily represent one coat) so any action on the hull will reduce the time your application of antifouling will last. Strong currents, frequent use, waters that contain higher levels of suspended sand or silt will all erode the antifouling and reduce how long it lasts.

How often should I antifoul my boat?

A frequent question but we feel it should be approached from another angle. How often do I want to lift out my boat?
If you lift out your boat every season for other maintenance reasons then you may want to refresh the antifouling. Purchasing an antifouling that promises three seasons protection is only worthwhile if you are not lifting out every season or, even if lifted out, you are happy to just clean off just green growth around the waterline. It is tempting to jet wash or scrub the hull once out of the water but you could be removing a whole seasons worth of antifouling by doing that, which is a waste. The simple answer to ‘how often should you antifoul your boat’ is - when it needs it. This can only be derived from experience and choosing the right antifouling in the first place.

Antifouling for boats on drying moorings?

We are sometimes asked about antifouling for boats on drying moorings. Our advice here is that there is no point in antifouing any part that sinks into silt or sand as the antifouling and any marine life is usually scrapped off at every tide. The rest of the hull should have plenty of coats of self-polishing antifoul but as the suspended matter is likely to be greater than normal it simply won’t last as long so a hard antifouling could be the answer.

Does a freshwater boat need antifouling paint?

First and foremost it is important to remember that antifoulings pollute. The open ocean and even coastal waters contain a significantly larger body of water to disperse biocides released by antifoulings. The same biocides that detract marine life are also very toxic to freshwater inhabitants.  Many freshwater moorings have restrictions on antifoulings especially lakes so it is essential you check this first. Secondly  it should be remembered that antifoulings are usually formulated to prevent marine life and not green growth. Self-polishing or eroding antifoulings may not erode in freshwater so making them useless after a short while. In short we cannot recommend any antifouling paint for freshwater use.

Remove bottom paint/antifouling from a boat

We suggest that owners learn to predict when their self-polishing antifouling have become depleted so that there is minimal removal of old antifouling. This saves waste and is better for the area around marinas if the wash off is not collected and disposed of. Hard antifouling does need to be removed once depleted and we hope that owners seek out a place to do this with the minimum amount of environmental impact. We recommend a product such as Strppit Antifouling Remover for this purpose.