It is a good idea to carry out an inspection of your boat’s hull condition as soon as possible after it has been lifted out and pressure washed.
Check all the surfaces of the hull below the waterline and remove any signs of remaining barnacles using a scraper. A few of these might still be found, as the pressure wash might not have dislodged them all and you do not want any of them gluing themselves to the hull as it dries out.
You also need to check for blisters. These may be caused by water being trapped under the paint or they could be signs of osmosis. If in doubt, then have an expert check them out for you.
Health and safety precautions
As antifouling is toxic and messy stuff, you must use suitable protective clothing. The biocides in antifouling can be absorbed through the skin so you need to protect yourself against this as well as any dust particles that you could breathe in. Wear a good quality breathing mask that protects you from solvents, also rubber gloves, safety goggles and overalls.
Lay down appropriate sheeting beneath the hull to collect any old paint and residue. You should check with your boatyard what the local regulations stipulate about removing and applying antifouling. You may need to use suitable tenting to protect others nearby.
Antifouling is one of the least pleasant boat maintenance jobs to do, but it has to be done. The very worst job of all is removing the old antifouling as this can get seriously messy and is very hard work.
The easiest way to reduce the build up of antifouling is by using eroding antifouling and to make sure that the hull is always pressure-washed as soon as it comes out of the water. Much of the remaining antifouling will be removed this way.
Antifouling in good condition
If the existing antifouling surface is even and there are few or no imperfections, then you can safely say it is in good condition. This means that preparing the hull before applying new antifouling will be comparatively easy whether you opt to go down the DIY route or ask professionals to do the antifouling for you.
Use 80-grit wet and dry abrasive paper to sand back the old antifouling. Be careful not to abrade too much as you want to keep the primer coat beneath intact. If in doubt, use 120-grit paper as it will be less abrasive. You need to keep the paper wet, so have a bucket of fresh water beside you to rinse in as you work.
When you have finished sanding, thoroughly rinse the surface with fresh water and allow to dry before applying the antifouling.
Antifouling in poor condition
If the surface is uneven and cratered, caused by patches of old paint that have flaked away and been progressively overpainted, then it is time to get your boat’s bottom back into shape. All the old antifouling layers need to be completely removed before new antifouling can be applied.
You may decide to employ a professional to do all this work for you and if you have the budget for this it will be money very well spent. Although this is the expensive option, it will save you considerable time, hassle and back pain. Remember also that applying antifouling in future seasons will be much more easy going.
Antifouling for metal components and hulls
Outdrives, stern drives, saildrives and propellers need special treatment. There are types of hard antifouling designed for them but before choosing these paints, you need to be sure what the components on your boat are made from.
- Most outdrives and stern drives and some trim tabs are made from aluminium.
- Propellers are made from bronze, aluminium or stainless steel.
- Drive shafts, trim tabs and other fittings may be made from stainless steel, steel or bronze.
- Keels are normally made from cast iron or lead.
As ever, it is worth checking with your propeller manufacturer’s recommendations before deciding which antifouling product to chose.
Antifouling for aluminium hulls
Antifouling with high copper content is not compatible with aluminium, so it is crucial for aluminium hulls to have several layers of primer to create a barrier between the antifouling and the hull itself. Antifouling that is made from cuprous thiocyanate is a good option but it still needs the correct type of primer beneath to protect the aluminium.