Typically we recommend a hard antifouling over the ablative types. Both have their place and limitations, particular to each, but both really only offer the same 12 month service life. It's a personal preference.
Our observation at Hardys Bay is that after 12 months, boats we service that have used ablative antifoul have more slime and shell than boats that have used a hard antifoul.
The types of antifouling available can be split into two types, hard and eroding. You will probably find other descriptions such as ablative, polishing or self-polishing. All these descriptions can be put under the umbrella of eroders.
Eroding antifoulings, as their name suggests, self ablates as the boat moves through the water. As well as while sitting in her Marina berth, the formulation of the paint allows the paint to continually ablate exposing fresh layers of copper or biocide.
Ablative antifoul is softer and wears away leaving eventually no antifouling on your hull. In theory, whilst there is antifouling on your hull it will give a degree of protection. With the current generation of paints however this does not happen because as the paint film starts to get thin, the biocides are preferentially washed out leaving paint that is essentially not antifouling paint. This is the time to apply new product.
The basic and original type of antifouling is the hard antifouling. When immersed and in a wet state this antifouling is hard enough, unlike ablative, and can withstand regular wiping down with a cloth, sponge or soft brush to remove the slime bacteria which precedes weed and mussel growth, without removal of substantial quantities of paint.
Hard antifouling does not wear away much at all, although abrasive material in the water such as silt and sand may lead to a very minor reduction in film build.
If you have a seriously fast boat or a fast boat that is used regularly then hard is probably the best way to go. Keen racing types sometimes prefer hard products as they can be wet sanded to a smooth finish prior to racing.
Boats moored in fresh water normally use these types, as the eroding types may not erode very well.
Eventually however, you are left after a few seasons with a build up of product that requires removal. The product becomes unsound and does not retain sufficient internal strength to be able to hold together when new product is applied to it.
However, in our opinion, hard choices are more environmentally friendly, as the build up could be properly collected and disposed of, where for the eroding types, it eventually "gets dissolved" in the water.
If you have decided that a hard type is your best option, International's Ultra might be your choice, a high strength product, suitable for all substrates except aluminium.
For aluminium substrates International's Trilux 33 is your best choice. Trilux is specifically developed for use on aluminum boats, outdrives and outboards.
If you have decided you want an eroding antifouling there are several choices for substrates other than aluminium.
International Micron 66 is the ultimate in antifouling performance even in the harshest fouling conditions. International Coppercoat is the lower cost option still able to give a very good all round performance.
For aluminium substrates International's Trilux 33 remains your best choice.
Copper oxide based antifoulings may be applied to hulls made of any material except aluminium. For steel hull, if not overcoating an existing antifouling, the International's Primer is necessary.
Most International antifoulings may be applied over most previously coated antifoulings directly, after a light wet sand, washing with water and allowing to dry. Overcoating of some may require a barrier coat of Primocon and other may require removal first.
Antifouling performance in general terms is dependent upon the film thickness applied at application time. International antifoulings are formulated to the optimum viscosity, or thickness. Thinning can significantly affect the application properties of an antifouling, and is therefore not recommended. Insufficient film build of antifouling is the largest cause of premature failure.
Areas on the hull that you would expect to have greater wear should have at least an extra coat applied, this includes areas that may get direct sunlight, such as the first half metre or so down from the waterline and any leading edges such as keel, rudder & prop wash areas.
Grassy growth and slime just love sunlight and are the most difficult species to ward off, so extra paint will help keep these obnoxious species away. Areas under the hull in the dark will generally not attract fouling species so readily and extra coats will not necessarily be required here.
It is a fact of life that when you launch your boat, the antifouling will not start working straight away.
It will take some hours for it to come to equilibrium with its surroundings. Meanwhile, floating around in the water are millions of small fouling species on the lookout for a clean surface to colonise and if you are unlucky enough to place your boat directly in a patch of such activity, the result can be premature fouling.
This problem can only be resolved by giving the surface a good scrub or light wet sand depending on the type of antifouling used - scrub hard types and light sand eroding types.
Another important point to remember is that the true colour of the antifouling will develop about 4 weeks after immersion.