Antifoul
How They Work
Antifouling paint keeps marine organisms, taking the forms of shell (animal fouling from barnacles and zebra mussels), weed (plant growth) and slime (single-celled algae) from attaching themselves to your boat. Most antifoulings use the dissipation of metal (on the hull’s surface and in the water) to prevent these nasty critters from adhering. Copper (cuprous oxide) and tributyl tin are two metals that have proven effective as biocides, but tin (finally banned worldwide on ship hulls only last year) was so poisonous that it decimated underwater ecosystems. Copper compounds are now most popular, but the price of the metal raw material has skyrocketed. Additionally, high copper concentrations dissolved in the water of harbours have created environmental problems and restrictions on application of cuprous oxide-based paints.
Antifouling Paint Choices
Copolymer/Ablative Paints
Copolymer paints release biocide at a constant controlled rate throughout their lives, wearing away or “ablating” much like a bar of soap. Paint wears off faster in higher drag areas on the hull and appendages. These paints work well in high-growth areas and continue to be effective after haul-out and relaunch. Copolymer paints offer true multi-season protection, lasting as long as there is a reasonable coating thickness. Because they expose new biocide until the coating is worn completely away, additional coats add to their longevity. We recommend a covering of two or three coats on the first application. Copolymer paints with anti-slime additives are best for heavy fouling areas.
Ablative paints (of the non-polymer type) work in a similar way and minimize the annual ritual of sanding when applying a fresh coat. Best use: Boats that are used often, but are not serviced by a diver. Not recommended when you want a super-smooth bottom finish and have a diver maintain it, since scrubbing removes paint and reduces longevity. Must be repainted if the boat is pulled out of the water for winter storage. All ablatives of both varieties share the advantages that they can be applied over most other types of antifouling paints and do not create a paint buildup.
Hard “Contact Leaching” Paints
If you keep your boat in the water year round you are most likely a candidate for a modified epoxy paint that prevents growth by leaching biocides upon contact with water. Contact leaching paint releases the biocide at a steadily decreasing rate, leaving the hard coating of the original thickness at season’s end. Higher copper content, rather than the type of paint binder as with ablative paints, generally means greater effective performance in this paint type. Modified epoxy paints adhere tenaciously to most surfaces, and can be applied over most types of paints. On the down side, they lose effectiveness when the boat is stored out of water.
Dual Biocides
Paint suppliers add a second biocide to some versions of their coatings, using formulas such as Biolux, Irgarol and zinc pyrithione and zinc omidine. These additives block photosynthesis near the water’s surface and restrict the growth of algae.
Aluminum Hulls and Underwater Metals
Aluminum hulls, outdrives and props require paints that do not contain cuprous oxide, which reacts destructively with the aluminum. Copper-based paints are safe for use on properly primed stainless and bronze. Zinc anodes should be left unpainted to retain their effectiveness.
Application and Prep Choices
If the old paint is known and in good shape: Remove old loose paint, dirt, grease, and marine growth with a power washer, brush or scraper. Wipe down with thinner/dewaxer or solvent wash. Sand with 80 grit paper. Exercise caution to avoid sanding through a barrier coat, if your boat has one. Repeat solvent wash. Clean with the thinner recommended by your paint manufacturer.
If the old paint is unknown and in good shape: Clean, remove loose paint, sand (80 grit paper) and rinse with water. Then simply apply the antifouling of your choice. Some slippery Teflon paints such as the Interlux VC Offshore series may need to be removed before applying a noncompatible paint.
If the old paint is unknown and in bad shape: Remove the old coats of antifouling paint. If the hull does not have an epoxy barrier coat this is a good time to consider applying this protection. Then proceed with painting.
Conclusion
Good preparation and priming are the basis for any paint job and antifouling paints are no different. Solid prep ensures good adhesion and better performance over time. Remember that most bottom paint changes color when exposed to air or water, so do not judge the color of your bottom paint on dry land. It will show its true color after a couple weeks of immersion. Don’t be too alarmed by a greenish hue of bottom paint near the waterline, due to the paint’s reaction with oxygen. It does not affect the effectiveness of the paint. If the look troubles you, paint the waterline with a hard antifouling paint and scrub it regularly.
What is anti-fouling Paint?
In salt water there are teeming thousands upon thousands of small creatures swimming along or carried by currents upon spawning. In the food chain size is important. The larger the organism the smaller the number of predators. However nature also provides some animals with the ability to feed while they are stationary, like mussels, oysters and barnacles for example. They feed by ingesting passing particles carried by currents and wave action. To resist the turbulance these animals have developed a highly sophisticated cementaceous adhesive which they use to anchor themselves to any surface. Just like the vaccum created by a rubber suction cup, but with a powerful glue. Once attached, these animals grow and propagate, creating colonies or clusters which in turn captures more passing food……. and so on.
On a boat that is constantly in the water this creates a significant problem, because left untreated the rudder, propellers, prop shaft and other moving parts will quickly become so encrusted with growth that they will seize up and become inoperable. This growth also creates significant drag to a vessels movement, adding to fuel costs and restricting hull speed.
The solution (?) Produce a paint coating that repels these organisms by creating a constantly toxic boundary layer of water next to the hull surface. These paints were designed to prevent the “fouling” of the surface by marine growth, hence the name anti-fouling paint. Although simple in principle, it proved extremely complex to perfect, because of the variations of conditions and toxin release rates. In cold climates toxin release rates were sluggish but so was the growth rate. Conversely in warmer waters the release rate increased, but so did the propagation of growth, meaning that the anti-fouling paint exhausted its potency much sooner than planned. Once depleted the growth explodes into being. The answer was to produce an optimum “middle of the road” product that would cover both cold and warm water conditions.
Adding to this complexity the environment also creates a pot-pourri of other intangibles. Rainfall, water temperature, salinity, tidal flows, localised pollution, effluent outflows, land mass phosphates/fertilisers…….. all contributing to this aquatic “soup”. Then we have photosynthesis which creates the slime, algae and grasses not repelled by the normal toxins. Although confined to the sunlight zone, this development also causes havoc with hull speed and visual ascetics…. and the problems do not end there.
Other creatures like Teredo Worm love the cellulose of wood. These animals will burrow into timber (when not repelled) and leave an entry point of a millimetre hole. Once inside they eat out the wood by “honeycombing” the entire plank and growing to a length in excess of a metre and as thick as a mans thumb. Next time you are down at a jetty, look at the timber piles and you will see the effect of Teredo Worm.
ANTIFOULING PAINT
There are 2 basic types of anti-fouling paints, hard and soft. Those that allow the release of the toxins through the paint film, and those that shed part of the paint binder/toxins in layers through friction. The latter are referred to as “soft” or “erodible” coatings. The “hard” or “contact leaching” types leave a spent coating of resin binder behind at the time of repainting. This means that the re-coating process builds on top of the existing film. Although this may result in some stripping of the paint layers in 12-15 years time it also helps to enhance annual repainting because there is a “reservoir” of remaining toxin in the old coat to enhance the performance of the new one.
Soft, or erodible coatings, were designed to give commercial vessels an economy of scale. If a boat had to undergo frequent slippings for routine survey inspections, then it was prudent to use an anti-fouling paint that did not last as long, but was easily washed off and replaced with a new coat……. eliminating buildup. Because this type works on friction it was necessary to impose a speed limit of less then 10 knots. Exceeding that speed simply tore the paint film off too quickly leaving nothing remaining when the vessel stopped.
Erodible anti-foulings were developed for the international shipping market where continuous hull friction created a “smoother” underwater profile by wearing away the high spots and as a consequence creating substantial fuel savings. This type of product has no advantage for a recreational vessel sitting on a mooring 6 days out of 7.
SELECTION
Here lies a minefield of controversy. Put 10 boating people together and raise the topic of anti-fouling and there will be 10 “expert” opinions on which product is best (and which ones are “rubbish”). Then there will be application advice on brush versus roller usage and what “brews” can be made to improve performance…….. chilli powder – sump oil – antibiotics – anti-fungal additives and so on. These do not enhance the performance of these paints and will affect the controlled release rate of the toxins.
The essential thing with all anti-fouling applications is to not exceed the prescribed coverage rate specified by the manufacturer. The correct film thickness (evenly applied) means that the toxic boundary layer of water will be uniform, and the performance likewise. Cutting corners by inadequate preparation, thinning the paint, or ignoring relaunch time minimums (drying times) will only lead to poor performance and increased costs later on.
Painting propellers require special attention because the vortex created, tears the paint from the leading edges and then continues to work back to towards the shaft. When stationary, the areas without anti-fouling will attract growth and eventually the whole propeller will become fouled and restrict movement. Only the “hard” types of anti-fouling (like Topflight) should be used. Several coats with emphasis on getting more paint on the outer edge is desirable. (see diagram 1) Allowing additional drying time is also worthwhile. Painting the propellers first will enable more coats to be applied and provide the longest drying times.
What are the Toxins?
All anti-fouling paints contain copper as the main repellent. There are 2 forms of copper:
Copper (cuprous oxide) and copper (cuprous thyocianate). The latter is less corrosive to
aluminium than the full blown cuprous oxide is but corrosive nonetheless. Other additives to
control slime/weed only play a minor role. The main problem is caused by barnacles,
tubeworm, teredo worm and only copper is a satisfactory deterrent.
This copper is released into the water by a controlled leaching process called hydrolising. This rate is 2.5 to 7 micrograms (millionths of a gram) per square centimetre per 24 hours. (see diagram 2) Within this range the paint will remain active for as long as the copper is being released. When exhausted, the marine growth will start to re-established within hours. The higher the copper content of the paint the longer it will take to be released, which
Limitations to colour range
The cuprous oxide levels in NORGLASS ANTI-FOULINGS dictate what colours can be
made. By using a low tint strength copper colours such as blue, black and green can be
created. Obtaining other colours are only possible by using the less effective copper
thiocyanate.
Selection
� Any vessel doing 10 knots or over should not use Soft Copper anti-foulings.
� Boats made of aluminium, or those with stern drives or sail drives must not use
NORGLASS ANTI-FOULINGS. Select a brand containing copper Thiocyanate and follow the manufacturers instructions to the letter.
� Boats doing less than 10 knots should seriously consider upgrading to the hard (contact leaching) anti-foulings as value for money is obvious. (TOPFLIGHT RED, BLACK or BLUE)
� Craft that use a travel-lift or crane for haul-out should not use Soft Copper antifoulings because the slings will tear the paint off upon re-entry. � Soft copper anti-foulings can only have more Soft Copper paint applied over them (brand irrelevent). To use a hard type, the old soft copper must be totally removed. � Hard type anti-foulings are generally compatible brand to brand and, given normal preparation, not a problem.
� Active consituents of all anti-foulings must, by law be stated on the main panel of the label. Comparing the price and the stated grams per litre (g/l) can influence the choice of product.
Considering that there are only a small number of manufacturers of anti-fouling paints (world wide), and with a vast tonnage of product used every year, (More than a million litres of antifouling on commercial shipping vessels sitting off Singapore harbour……..any day of the week) illustrates the magnitude of the problem. Globally, scientists have tried Silicones, Teflon, Lanolin, synthetic compounds and an assortment of other ideas to resolve the problem of fouling…….without success. With a lead time of 7 years (minimum) to produce a new anti-fouling paint, plus the investment in R & D……..to make a better mousetrap is a hard ask. Consider this aquatic soup. Rainfall variations, land mass development run-off, temperature variables, salinity levels, topography, tidal flows, effluent outflows, fertilisers and so on………..plus human pollutants, all have a contributing role on how successful the coating will be.
Removing old Antifouling
On surfaces such as steel, aluminium or wood the most practical ways are either by paint stripper – wet sandblasting – or a “poultice” technique which uses a paper over a coated solution and then gets peeled off. Last option is to wet sandpaper the surface.
Because the toxins are potentially hazardous, dry sanding is not an option. Any removal of old anti-fouling paint must be done responsibly, so that all of the removed material is contained, or captured before it has the opportunity to reach the water.
Removal of anti-fouling paint from fibreglass can cause some additional headaches because the use of chemical paint strippers can affect the integrity of the gelcoat. If a slow reacting paint stripper is used, only small areas should be coated at any time so that the paint/residue can be removed before the stripper has time to react with the gelcoat surface.
Storage
Anti-fouling paints are normally very dense (heavy). A can of Topflight Red for example weighs-in at more than 2kg per litre. As a result the copper settles in the can faster than other paint products. In order to keep the copper in suspension, the tins should be turned upside down once a month to prevent compacting of the contents. Meticulous stirring is essential, right up to the time of applying.
Consider this: If a tin of anti-fouling has been sitting on a shelf for a few weeks, the weight of the copper will want to sink lower in the can. Therefore, if the tin is opened and just painted on, the first 20% of this product will have a lower copper ratio. Then as the residue arrives at the surface, it will be disproportionate with a copper sludge, and less formulated material, to provide the correct rate of dissolving.
If this happens there is no way of providing an overall controlled release rate of toxins. Some areas may begin growth within days/weeks.
In a nut shell
. • Make sure the surface is properly prepared and dry.
. • Read and follow all of the manufacturers instructions.
. • Calculate the area to be painted and divide by the coverage rate per square metre to determine how much anti-fouling paint is to be applied. Do not exceed this rate. Any left over anti-fouling is best used up by coating turbulent areas such as the stem, propellers, planing strakes and around the waterline.
. • Observe the launch time so that adequate drying time occurs.
. • Avoid using the motor until the paint is well set and hard. The vortex created by the propellers can strip off uncured anti-fouling very easily.
. • Stir thoroughly before use and do not thin or add anything to the paint.
. • Do not allow any anti-fouling scrapings to enter the waterway and respect the environment by correct disposal of empty cans and used equipment.
. • DO NOT use NORGLASS ANTI-FOULINGS ON ALUMINIUM AS SEVERE CORROSION WILL RESULT.