Hull Cleaning (Fouling Types and Bottom Paints)

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                       The increased coast for fuel for vessels operating at normal cruising speeds with a fouled hull can be averaged at 10-15%. These figures seem to be true for all types of vessels and were derived from consensus, opinions, and documentation. In most cases an underwater hull-cleaning job of even a slightly fouled vessel will pay for itself in fuel savings alone.

            In the case of sailboats, even a light film of slime can have a serious effect on performance. The hull of a sailboat is designed to be slippery to create as little drag as possible. Where a powerboat can compensate for marine growth by advancing throttles, a true sailor does not want to fire up the engine to compensate for loss of speed!

            The first stage of fouling is slime. Slime formation begins by bacteria attaching themselves to your hull. This process usually begins within a half hour of being in water.

Slime alone can increase fuel consumption by as much as 15%. Anti-fouling paints are designed to repel these microscopic intruders by releasing toxins into the layer of water next to your hull. Your anti-fouling paints’ leaching of toxins, initially, works well. As time goes by, the dead bacteria build up as slime and begin blocking the leaching toxins.

The dead bacteria forms a foundation upon which more advanced forms of marine growth will develop.

            Stage two fouling is multi-cellular grasses. These green grasses depend on light for photosynthesis and, therefore, tend to concentrate at the waterline and sunny side of your vessel. At depth, the color of grass accumulation changes from green to brown. Any grasses growing on the side of your boat should be removed on a monthly basis before their roots take foothold. If not, the grasses will leave permanent stains and may cause paint to lift away from the hull. Topside enamels and boot stripes are not as tough or thick as hull coatings. If grasses are left to accumulate, a more aggressive abrasive action will need to be used to remove them possibly resulting in bare spots in the paint. Clean Hull Diving Services always uses the least abrasive, but effective, brushes to prevent paint wear as much as possible!

            Stage three fouling is calcareous organisms. These begin as free-swimming, microscopic organisms, and attach themselves to your hull. These calcareous organisms develop into creatures that can inflict severe and permanent damage to your vessels hull.

Barnacles are the main organisms found in stage three fouling. These are usually acorn and/or goose barnacles and tubeworms. They are found from waterline to keel and will constitute the dominant type of fouling on propellers and running gear.

            Stage four fouling is the composite of the first three stages, but includes soft sedentary animal growth. Together with the other types of fouling, stage four fouling becomes a dense growth covering a greater portion of the hull. The sheer weight of this growth can be tremendous. One square foot of marine growth, one inch thick, can weigh as much as 3 pounds!


Bottom Paint


            Bottom paint can be of two basic types soft ablative or hard anti-foulant. Ablative coating also called“ Free-association” paint is soft and allows the release of more toxins into the environment. Bottom paint incorporates anti-foulants to discourage marine growth. The hardness or softness of your paint is dictated by the quality, combination, quantity and type of resin. Ablative type copolymer paint is ideal for sailboats in that it remains smooth causing less drag. Boats painted with soft ablative coatings must be launched within 48 hours of painting to retain effectiveness.

Hard Anti-foulant paint utilizes “contact leaching.” The paint dries to a pours film that is packed with Biocides which leach out on contact with water to prevent fouling growth. This leaching will usually release biocides throughout a season but the amount of toxins released steadily decrease until there is no toxins left to maintain fouling protection. Once the biocide is exhausted the paint remains on the boat. This type of paint is more resistant to abrasion. Boats using hard anti-fouling paint should ideally be hauled out for paint recoating when toxins have leached out and no longer offer adequate protection. If your boat with Hard Anti-fouling paint is hauled out for an extended period of time, the paint as well as the biocide will oxidize preventing leaching of toxin. Again it should be sanded and recoated before launching.

The most effective anti-fouling agents are metals such as lead, copper, mercury, tin, and arsenic, plus some newer compounds we will talk about. Mercury and arsenic have been banned for use in marine bottom paints. Copper is the most common toxic agent currently in use.

The application of your anti-fouling paint should be in several thick, semi-soft layers on a clean, smooth hull. We recommend a minimum application of two coats of paint with additional coats in areas prone to wear. Your hull should be submerged in water before the paint fully dries because hardening of the paint tends to limit release of toxins. All divers working for Clean Hull Diving Services LLC are careful to avoid removing more paint than necessary when cleaning your hull!


There are a multitude of anti-fouling paints available for use on your hull. All anti-fouling paints use a combination of various toxins and biocides. The most toxic agent currently used in anti-fouling paints is copper. Copper is usually added to vinyl paint they call cuprous oxide vinyl. This paint is available in various brands and colors. Your paints effectiveness depends on regular maintenance with proper cleaning and rejuvenation techniques. Proper maintenance will double the life of most anti-foulants. Clean Hull Diving Services LLC will maintain your anti-fouling paint to keep its maximum effectiveness.

            In recent years some conventional anti-foulants have included an agent called Organotin as a biocide. This agent could be present alone or with a combination of copper and other toxins. The chemical tributyltin (TBT) is found in Organotin anti-foulants. The rising level of this compound in coastal waters has proved to be detrimental to marine life. The ultimate ban of organotin-based anti-foulant paints will be a victory for environmentalists, the fishing industry, and for underwater service experts as well. Please inform us if your vessel uses an organotin-based paint. The health and safety of our divers takes presidents over the cleaning of your vessel. See Restrictions on the Use of Marine Antifouling Paints.”


Copolymer bottom paints are more effective and longer lasting than conventional anti-fouling paints. Copolymer bottom paints differ from other bottom paint in that the toxin is mixed in with and chemically bonded to the paint itself. In conventional bottom paints the toxic agent is a separate additive where chemical poisons are suspended in the paint film. The toxins gradually leach out and leave the paint behind without effective toxins. This often leaves tiny cavities in the surface of the paint. This doesn’t happen with copolymer paints. As long as copolymer anti-fouling paint is cleaned periodically to remove any stage one slime fouling, the paint should remain just as effective as when it was first applied. As long as a coating of paint remains on your hull, however thin, it will have the same toxicity as it did when it was first applied.


            Self-Polishing Coatings (SPC’s) is another category of anti-fouling paint. This type of paint is primarily used on high speed commercial vessels. SPC’s are a type of copolymer paint designed to slough off surface growth while the vessel moves through the water at high peed. These coatings do not perform effectively unless the vessel is always moving at a high rate of speed: so, they are not really suitable for most ships. SPC’s are very expensive and can’t be applied over existing paint. Even SPC’s must be periodically cleaned by divers because they build up marine growth quickly when vessel is idle.


            An underwater maintenance program is essential to assure maximum performance and longevity from every type of anti-foulant paint.  For maximum effectiveness and longevity it has been determined that anti-fouling coatings should be cleaned whenever a coating of slime and incipient grasses have developed. At this stage, with a light brushing, we remove all growth, plus an ultra-thin surface layer of anti-foulant coating to renew the surface, allowing the toxins to be released again with the same effectiveness as when the coating was first applied. All anti-foulant coatings are expensive to purchase and apply not to mention the haul-out cost. Use Clean Hull Diving Services to keep your hull clean and prolong time between haul outs!

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