The Science of Fouling - SailNet Community
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The Science of Fouling

Every boat owner who keeps his or her craft in the water on a long-term basis must face the issue of fouling, which means periodic haulouts for most boats.
Every year sailors who keep their boats in the water go through the ritual of prepping the boat’s hull and applying some form of antifouling. There are numerous approaches to keeping your boat’s bottom free from growth—and it’s obviously important; that’s why an entire industry has grown up around this need. But what do these sailors understand about the cause of their actions? Why is it they’re forced to endure this bottom-painting ritual? If you’ve ever wondered about the reasons behind the existence of antifouling products, you’re not alone. Read on for a better understanding of why we all go through the drill every year.

There are three basic types of bottom fouling, each of which has its own characteristics:

Shell species
such as barnacles and zebra mussels release millions of veligers or larvae into the water, which in turn move around in the currents. Because the nutrients these creatures need to grow into fully developed adults are suspended in the water, they have difficulty feeding and therefore look for static objects where they can attach themselves. As most boats remain static 90-percent of their time afloat, they offer extremely suitable feeding grounds for all types of fouling.

Weed comes in a variety of forms. Static objects will attract common seaweed, many forms of which will simply fall off when a boat hull begins to travel through the water. However, some weeds such as Brown Weed, are more resilient and can withstand quite high speeds through the water.

Weed and slime can foul a hull and slow you down, but the consequences of barnacles clogging an engine intake or centerboard trunk can be truly dire.
is the other major form of fouling, and this one presents a formidable challenge to the antifouling chemist. Slime is caused by billions of single-celled algae that produce a syrupy medium in which to settle. In common with many types of fouling, once established, this medium provides an ideal settling ground for more algae. Hence coatings of slime can grow quite thickly on a surface and will remain on the hull as it moves through the water.

Why does fouling vary so much between areas? Different water qualities and temperatures produce different types and breeds of fouling. The differences can be quite dramatic, even in one region. This is due to outfalls, pollution, inflows from rivers and streams, the flow speed of the water, and even shading from cliffs, trees, and buildings that reduce sunlight. Once fouling has established a hold on a boat’s hull, it will rapidly spread or colonize the surface. Prevention is therefore a better approach than seeking some other cure or attempting to remove the fouling by periodic cleaning and scraping.

There are a number of key reasons to keep your hull free from these sources of fouling. Safety is the principal reason. Heavy fouling growth reduces the responsiveness of sailboats and powerboats as well. In extreme cases, the extra weight of the fouling can make the boat sit lower in the water than intended. This can have obvious implications in heavy-weather conditions.

Protecting your hull is important because prolonged fouling can penetrate and weaken the substrate.
Protection of the vessel is also important. Prolonged growth of certain types of fouling can damage the substrate of the hull. For example, the natural glues used to attach organisms to the hull can damage wood and fiberglass. And of course fouling can also clog water intakes, resulting in damage to the engine.

Speed and efficiency also figure into the reasons why you’d want your hull to remain free of fouling because extraneous growth or materials on the hull cause drag. As drag is increased, fuel consumption increases and speed is reduced even to the point where a planing hull may not be able to get up on plane. For racing sailboats, this can be the difference between winning and losing, and for offshore and coastal cruisers, it can mean that a voyage takes longer than planned, which in itself has any number of consequences.

Recreational and commercial craft have been battling the fouling issue for centuries, and some progressive resolutions have begun to appear (see sidebar).

Keeping it Clean

All sailors who keep their boats in the water must contend with marine growth, but we can all learn to do so in ways that have a lesser impact on the marine habitat around us. First, we can consider using antifouling paints that are nontoxic or have a lower copper content and a hard slick surface. (Hard paints tend to release their toxins into the water and a lesser rate.) And regular underwater hull cleaning can help control fouling growth between haulouts. However, boats with soft, rapidly sloughing or ablative paints shouldn’t be cleaned underwater because this unnecessarily releases more toxins.

Because the additives in bottom paint that deter marine growth also have been found to cause major damage to marine habitat, the evironmentally concerned boat owner should consider all the options. Here are a few alternative approaches to antifouling. Lack of experience with each makes difficult for us to offer recommendations, but they’re worth investigating on your own:

Sounding Off    The manufacturers of a number of different devices tout success with sonic antifouling. One that goes by the name Barnaclean features small electronic nodes installed inside the hull that create a low-frequency "shield" to keep the hull free of growth. The system reportedly uses a miniscule amount of current.

Smooth Skins   Synthetic coatings designed to repel growth, such as Marine Skin, boast no cacinogens, nor copper or tin. Some, like Seal Coat are silicone based and use a series of electrostatically charged microfibers to repel growth. Others like Wearlon boast self cleaning properties if your boat travels as sufficient speeds.

Suggested Reading:

The Bottom Paint Blues by Don Casey

Combatting Bottom Growth by Mark Matthews

Spring Hull Cleaning by Tom Wood

SailNet Store Section:  Cleaners, Polishes, and Coatings

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