Biofouling

An Age-Old Problem:

Bio_Fouled_Closeup

Close up of 8 months of growth on a sailboat hull.

An Extreme example of a fouled hull.

 

 

 

 

 

 

 

 

Once a boat or ship is placed in the water, either saltwater or fresh, marine growth or bio-fouling begins to accumulate. It starts with algae and quickly progresses to brine shrimp, barnacles, grass, lettuce, tube worms and other varieties of marine organisms and sea monkeys. A general rule is: The warmer the water, the faster the growth. This process can begin to occur in as little as two weeks but is retarded by the application of anti-fouling paint (bottom paint), which is poisonous to marine growth. There are two basic types of anti-fouling coatings: soft (or ablative) and hard.

Soft bottom paints rely on a fine layer of paint sloughing off the hull to remove the bio-fouling and require frequent recoating.

Hard bottom paints rely more on poison or extremely slippery, non-stick compositions (Teflon). The typical poisonous compound used in both soft and hard paints is copper with proprietary additives depending on the manufacturer.

Regardless of paint type, within a few months of the new paint’s application, marine growth begins to form. It creates a rough, irregular surface which in turn creates hydrodynamic drag, reducing performance and increasing fuel consumption.

For example, on a typical 40-foot motor sailboat, a clean hull will yield 7 knots (about 8 miles an hour) at full throttle. With a moderately fouled bottom, maximum speed will be reduced to just over 5 knots at full throttle, an efficiency reduction exceeding 30%. On fast powerboats, moderate fouling will reduce the performance to the point where eventually they cannot get up on plane; a power boat that normally makes 20+ knots, tops out at only 8 or 10 knots. More fuel is burned yet less distance is covered. Expecting good performance from a boat with a fouled bottom is like applying shag carpet to the wings and fuselage of an airplane and expecting it to fly. (Fortunately, the boats still float!)

A Little History:

Careened_Tallship

 

 

 

 

 

 

 

 

 

 

 

In the days of the tall ships, the entire hull below the waterline was covered with pure copper panels nailed or screwed in place. As steel and iron ships replaced wooden vessels, paints were manufactured from extremely poisonous substances including lead and a chemical compound of tin (organotin). With society’s increasing awareness of human effects on the environment, these highly toxic (and highly effective) methods of controlling growth have been phased out in most countries.

These environmental concerns are only increasing. California and several other environmentally progressive states are considering legislation removing copper from all bottom paints and have already reduced the allowable copper content of existing coatings, making the problem (from a boat owner’s perspective) worse, by increasing the frequency for hull cleaning. The modern paints simply don’t work as well as the older compounds.

How Boat Hulls are Cleaned:

All boat owners who keep their boats in the water for any length of time, whether in a slip in a marina, or on a mooring in the harbor, or on a trailer for the winter, are painfully aware of the necessity of keeping their hulls free of bio-fouling.

There are three basic methods of removing bio-fouling:

Sail or motor the boat through a large patch of kelp. Although this appears to be the most cost effective way, there are substantial risks, such as wrapping your keel, propeller or rudder with kelp. It inevitably leads to the next method:

Dive the boat. Either hire a commercial diver or do it yourself (or get your crew/kids to do it) by scrubbing the hull with brushes, scrapers or pads made from abrasive material.

Haul the vessel out to strip and repaint. This process is expensive and time consuming. It is inevitable that a boat be “hauled” for maintenance; the object is to delay this type of expense.

By far the most popular method is hiring a professional commercial diver to clean the hull on a regular basis. Hull diving enterprises are generally small one- or two-man operations with a list of repeat clients. They are usually confined to a particular harbor or marina (although there are some that operate in multiple harbors and have numerous employees) and perform other vital underwater maintenance tasks in addition to cleaning.