Antifouling your multihull

By Michael (Nod) Crook

Service Manager, Multihull Solutions

I am regularly contacted by owners of new and pre-owned catamarans who want to know how to best go about their first haulout and re-antifoul.

There are many things to consider before undertaking this routine maintenance, and I have outlined some of these below:

 DIY or contracted

A lot of people imagine they will save a considerable amount of money by taking on this challenge and doing the work themselves. However, you may be pleasantly surprised at some of the lift, hardstand and re-antifoul packages offered by boatyards. They buy product in large quantities and can usually supply at good prices. They also normally spray the antifoul which gives you a better finish, an even coverage, and reduces the labour time.

For those going it alone, make sure you take into consideration the products you are dealing with. Most antifouls contain copper (cuprous oxide) as well as other chemicals. These prevent the growth on your hull but are also very toxic. You need to make sure you are wearing protective clothing while sanding and re-antifouling. Make sure you only wet rub the hull to keep dust to a minimum. If you do have to dry sand the product, make sure you wear a respirator.


A properly applied, good quality antifoul should last up to two years. With ablative products this is, of course, dependant on how much is applied to the hull and how far the boat sails during the time period. For those heading off on extended cruising, often to remote areas with poor facilities for lifting larger catamarans, a good antifoul before departure is recommended.

For some owners, the haul out is an annual occurrence as they want to polish hulls, check rudder bearings, replace anodes, clean through hull fittings and engine pick ups.  In this case, a light application of a cheaper product may be all that is needed to keep the boat clean for 12 months.


If you are re-antifouling your boat for the first time, you may be unsure of what product has been applied to the boat previously. Make sure you seek professional assistance and are buying a product that is compatible and will adhere to the existing product.


There are many different types of antifouls for different applications. For most cruising catamarans, the boat stays in the water all year round, and so the products below do not include those for boats on the hard or for serious race campaigners.

Standard Ablative Antifouls

These deliver the copper biocide to the surface by gradually dissolving or “ablating”. As the antifoul wears, a fresh dose of copper goes to work preventing weed and growth from forming. Ablatives are good 1-1 ½ season paint.  Note: You need to apply more to the high-wear areas like the front of the hulls, keels and rudders. Ablatives do not build up like epoxies and so only require a wet rub before re-application.  Note: Most ablatives cannot be hardstanded for long periods without losing their effectiveness.

Epoxy Paint Antifouls

This leaves a non-erodible painted surface. The copper biocide leaches through the base paint when in contact with water and continues until it has all gone.

The paint remains after the copper has gone. For this reason the layer needs to be fully sanded back before the next application.

A high copper content is key to the longevity of each particular product. These antifouls can also require a regular hull clean in high growth areas.

True Epoxy-coating Antifouls 

These antifouls are an epoxy-based paint containing copper. Coppercoat is the most well known one of these. The coating has to be applied over a bare fibreglass bottom or epoxy barrier coat and will survive repeated haul outs. The copper biocide slowly comes out of the paint and will last for several seasons or more. Due to the copper content and longevity it is the most expensive. Coppercoat makes a lot of sense for remote cruising or to protect your boat for many seasons.

Ultrasonic Antifoul

I have included this product as an alternative to the norm. It regularly comes up in conversation and has very conflicting reviews. Some manufacturers claim that once installed you never need to antifoul again. I have heard a few good reviews of it working well as an addition to an antifouled hull. I will let you all make up your own mind!


There are primers available that you can put on your propeller to allow you to antifoul it. For boats that are not used or scrubbed regularly, this is a good idea as growth will start very quickly otherwise. Prop Speed has become a very popular choice for applying to props, shafts, struts and thrusters. It is a two-part application. The first is an etching primer to the bare prop. The second is the clear coating that leaves a very smooth surface growth should not stick to. The success of Prop Speed is in the correct preparation and application. If done badly, it will not adhere to the propeller for the required duration.

If you spend the time prepping and re-antifouling your boat correctly you will enjoy less maintenance and faster boat speeds all season.

Good luck!

Nod Crook

Service Manager

Multihull Solutions

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