Antifouling, what you need to know.

FUBAR. Fouled up beyond all recognition

Noun

Treatment of a boat's hull with a paint or similar substance designed to prevent fouling.

"antifouling bottom paint"

There is a lot of disinformation about antifouling paint, look around at some questions on forums, conflicts of opinion worse than if discussing politics. Let´s try and keep it simple. If you trailer your boat, do not leave it in the water for more than very short periods then you do not need to antifoul the bottom, otherwise you should consider getting the wet underwater surface painted.

Why antifoul?

The wet surface (underwater) part of your boat sits in the water, doesn't matter if its fresh or salt water, it contains organisms that will stick to the hull of your boat. The cleaner the hull, the faster the boat will go, use less fuel and produce less emissions.

Apart from the obvious benefits of economy, hull growth forces engines to work harder and so can run hotter, the sea water intakes can get partially blocked and cause all sorts of problems, antifouling helps to reduce this. Something that is often misunderstood and we should get clear now, no antifoul is 100% effective, there will always be some growth, how much depends upon geographic location and how often the boat is used.

How antifouling works

Quite simply really, the paint contains biocides, ingredients that kill marine growth. The paint has a leech rate, this means how much of the poison (that´s what it is they just don´t say it), whatever growth is on the surface of the painted hull will start to die, as the boat moves that dead growth will fall, exposing more paint to repeat the process.

One important thing is that not all paints are compatible with all hull materials, wood and GRP (fibreglass) tend to be the least finicky, however aluminium and steel will not be able to be coated with any kind of topcoats and, may require a particular kind of primer.

Hard or soft?

There are two basic types of "normal" antifouling, split into two groups, these are hard and soft types, each has its uses on different types of boats.

Soft

Also known as self polishing or self/auto eroding, as the boat moves through the water, the antifouling erodes, the growth falls away and more of the paint is exposed underneath. Soft antifouls are generally suited to "slower" boats, sailboats and powerboats who tend not to cruise at higher speeds, say the high twenties, the paint would erode too quickly for such sustained cruising.

When hauling out, the yard will use high pressure cleaners with jets of water than will remove this kind of paint. In order to take full advantage of how this paint works, the boat needs to be used regularly.

Hard

Does not erode like soft antifoul, the major benefit of this kind of paint is it can be scrubbed, that is, cleaned, rubbed or even jet washed providing you´re careful. For boats that have very high cruise speeds this works well, racing yachts will apply this hard formula and gently sand the surface for the best possible finish. I would also suggest this kind of paint for the many boats that seem never to move from their moorings except to go to the yard.

Specialty antifouls

Coppercoat is an epoxy resin (two part product, resin & hardener), each litre is mixed with about two kilograms of copper powder, it is non leaching and regarded as more environmental than other types of antifoul, it also has a very long life expectancy, some boats claiming not to need a new coat for ten years.

Coppercoat does require some surface prep and you cannot use certain chemicals for preparation as the epoxy will not adhere well. When the vessel is hauled for bottom cleaning (usually quite a quick affair with this type of coating), the antifouling is sanded to reveal a new coat of the product before relaunch. Coppercoat when first applied is literally the colour of copper, when it has been in the water for a while, it goes a sort of pale green, anybody who has see corroded copper wire or tube will know, apparently the cuprous oxide (green colour) is especially distasteful to marine growth.

I can testify first hand to the effectiveness of this kind of antifouling, what I think puts people off using it is not all yards make a good job of the preparation or the application, there are detailed instructions on how to apply this product, it´s not difficult, just has to be done as per the instructions, I have found the most effective method is only do what you can achieve in one day, the subsequent coats (you can apply many) go on "wet on tacky". Another consideration is cost, especially when you have to remove completely strip the hull of any old antifouling paint.

Propspeed This is not an antifouling in the normal way, it does stop fouling but does not do it by releasing any biocides, it is a marine coating that stops growth from actually being able to get a grip. It is used for propellers and rudders mostly although other products are available for underwater lights and transducers. I have no clue what it is made from but again, I can testify to it´s effectiveness, when you touch the coating it feels like a rubber or latex, bit like a mechanics glove or a birthday balloon.

Silicone based antifouling. I have included this in the specialty section for a reason, even though silicone based antifoul has been around for a while, it seems a bit slow to have really penetrated the market.

The really important thing here, is selecting a biocide free silicone antifoul, there are other types, but we do not want silicone being leeched into the water. The silicone based paints create an oh so slippery surface (more on that in a minute) that when the boat moves, growth has a much harder time staying attached. I have heard nothing but good things about this kind of paint, including tie coats that allow it to go over conventional antifouling without having to strip back to the bare hull.

Slippery little sucker. I said we´d get back to how slippery this stuff is, some yards are less than happy about lifting boats painted with silicone based antifoul, when investigating the reasons, I found out that it´s so slippery, especially when it has a very thin layer of slime or algae growth, that the strops in the travel lift actually slip. This is easily overcome by using ropes to tie the fore and aft slings or strops together so they cannot move, don´t be surprised if there is a surcharge for this service.

First time painting

You might be able to order your new boat already bottom painted from the factory, if not you will need to get it painted for the first time. If a dealer is arranging this, they should have enough experience to know where the water line is and get straight to work, if not there is a simple process;

Put the boat in the water, if it is not already at it´s maximum displacement (full of fuel, water, supplies etc.), you might have to add weight in order to simulate the water line. Leave boat, come back some days later and have boat hauled, there should be a nice dirty line to show you where to antifoul to. The alternative method, same as number 1, some yards simulate the weight with workers from the yard (cue many jokes about weight loss), then toss sawdust in the water around the boat to mark the water line. It allows the boat to stay in the water for the minimum time.

Marking & cleaning, bow we have our guide, we have to get a wax pencil or crayon and mark the line made in the water, mark the line in several areas, now clean off and sawdust or loose fouling.

Sanding & taping, the shiny gelcoat will not allow the paint to bond correctly, the finish must be abraded, how you go about this depends on how big the boat is, either using a sander or by hand. You might be surprised as to how coarse of paper you need. The sanding pads made of a fine metal mesh seem to work very well for this, remember to use a mask, you are trying to achieve a uniform matt finish, not gouge and you are trying trying to achieve a fine finish like you would for varnish. 

Final step before primer is to mark the waterline with painters tape, hopefully you haven't removed the marks you made previously. If you will finished painting in a short time, no more than a few days, regular "yellow" tape will be fine, if the tape will be left in place, one of the other "low tack" or similar tapes should be used, this type of tape will not leave a sticky residue behind when removed.

Prime, for the top coats of antifouling paint to stick, the first coat must be a primer, this will form the bond between the freshly sanded gelcoat and the topcoats. Primer is usually grey, this is useful to highlight where still needs painting, before priming or any painting, make sure there is no dust on the surface to be painted and also read the instructions of the product.

First coat, Following the instructions, first coat of antifoul goes on following the primer, due to the primer being grey it is easy to see where to paint. The most effective method for painting both top coats and primer is to use a roller, some products will recommend a foam roller, others a short pile type, no long pile or texture type should be used. For cutting in around skin fittings, rudders etc., use a bush, make sure you remove any hairs lost from the brush.

Second coat, Consider using a different colour of antifoul for the second coat, the contrast will allow you to see where still needs painting and will serve as a guide in the future which areas a losing the most paint and when it´s time to haul the boat for a fresh coat. Subsequent coats of paint when hauling out can be one or two coats depending on how much has been lost.

Then what?

Well, if you have finished bottom painting, take a step back, admire your work, leave the boat in the yard for the required time for the paint to cure, pay your bill and launch your boat, go boating, have fun adventures.

Recoating

Well, nothing would be that simple would it? Antifouling will require recoating, in the past it was an annual affair, now I have been seeing the same boats getting recoated every 10 months, this is probably more noticeable with the soft antifouls, the reason is the same sorts of chemicals used in previous years can no longer be used, so the function of the paint is affected. For those people who do not use their boats that much, I would not worry too much about brining your boatyard visit forward.

If the antifouling looks like this, it might be time to strip it

Starting over

After many years of coats of antifouling, it does become necessary to start from scratch, navigating more often, you may be able to go many years without stripping the paint off and starting over. In order for the paint to work effectively the surface needs to be as flat as possible, not like the surface of the moon. It´s always a good thing to go back to the original underwater surface for a proper inspection.

A good way to judge when it´s time to strip the antifouling is when you feel a thick edge of paint at the waterline, a bit like when brake discs start to wear and you can feel that lip on the edge.

Antifoul stripping & removing

Blasting

This is a professionals only service, a machine is used to fire a media at the hull removing the old layers of paint and primer, going right back to the hull surface. It is extremely effective and there are more kinds of environmentally friendly medias available, such as soda or wet sand that can be recovered and at least partially reused. The downside is it can make a lot of mess, often yards insist that curtains are erected around the boat to contain the process.

Sanding

You can do this yourself, but please use a mask, goggles and either a protective suit or clothes that you do not mind ruining. One other thing to remember, prolonged use of vibrating tools is not good for you, if your hands start to feel funny, stop. This is probably the most common method of removing antifoul, you can get sanders with vacuum attachments and makes life much cleaner. It is whichever way you do it, time consuming, something to think about when on a daily rate of hard standing in a boatyard.

Chemical stripper

This is something you can do yourself. I have seen two types, one that softens the paint like any other paint stripper, the hull is then scraped and the paint comes off, or the hull can be jet washed. This method can make a lot of mess and obviously paint stripper can be nasty stuff, use with precaution. I am not sure that water blasting the old paint off is very friendly to the environment.

The second method is a chemical stripper with a cover sheet, I have used this method first hand, it was sold by peel away A test patch is done first, determining how many hours the product has to be left on. The plastic sheet, when removed brings all the layers of old paint with it, keeps the mess to a minimum, keeping you in the yard managers good books. On reflection, the yacht we stripped, I think the owner was too eager and we should have left the stripper on for the maximum 48 hours, for my liking we had to do too much sanding after.

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