How does antifouling work? Which one to choose?

Andaman 50 

Regular antifouling renovation is a key step in the maintenance of your boat, to ensure speed and energy savings.

Disclaimer: The purpose of this article is to provide information on the various operating modes and main categories of antifouling, but it cannot replace professional advice.

How does it work? Which antifouling category to choose?

How does it work?

Biocides release:

Today's most effective conventional antifoulings are all based on the same principle: the application to the hull of a product containing biocides, substances which are toxic to marine organisms. These biocides slow down, or even prevent, the settlement of marine fauna.

The products used in antifoulings are varied, each with specific properties designed to prevent the adhesion and development of marine organisms on boat hulls.

Here are the main compounds used:

Active compounds (Biocides) :

• • Copper (Cuprous oxide, Cu2O) :
    Function: Copper is widely used for its biocidal properties against algae, shellfish and other forms of biofouling.
    Mode of Action: Copper releases toxic cupric ions that inhibit the growth of marine organisms.
    Considerations : Although highly effective, the use of copper is regulated in certain areas due to its potential impact on the environment.
• • Zinc Pyrithione :
    Function: Used as an alternative to copper, it is effective against a wide range of organisms.
    Mode of action : Disrupts cellular metabolism in marine organisms.
    Considerations: Less problematic for the environment than copper, but still subject to regulation.
• • Tributyltin (TBT):
    Function: Formerly widely used for its effectiveness against all types of biofouling.
    Mode of action: Interferes with enzyme synthesis in marine organisms.
    Considerations: Banned worldwide in 2008 due to its devastating impact on marine ecosystems.

Alternative Biocidal Compounds :

• Diuron: A herbicide that inhibits photosynthesis in algae.
• Irgarol 1051 : A biocide effective against algae and certain forms of shellfish, but its use is restricted in certain areas due to its effects on aquatic plants.
• Chlorothalonil : Used mainly against filamentous algae.
• Theophane-Methyl : A fungicide that can be included to combat fungi and other micro-organisms.

These compounds are then released using various mechanical processes, more or less adapted to the type of boat, its use and the environment in which it evolves.

Hard Matrix:

• How it works: Biocides are encapsulated in a hard, non-wearing matrix. Biocides are released by diffusion through this matrix.
• Efficiency : Constant diffusion makes this type of paint suitable for boats that are not in constant motion.

Erodible die (Auto-erodable) :

• How it works : Paint gradually wears away with the movement of water. This controlled erosion releases biocides at a constant rate.
• Effectiveness: As paint wears away, it always reveals a fresh surface with active biocides, which is particularly effective for boats in frequent use.

Controlled hydrolysis :

• How it works: The paint matrix breaks down by hydrolysis (reaction with water), releasing biocides in a controlled manner. This chemical reaction enables a gradual but constant release.
• Efficiency: Offers long-term protection with uniform release, even when the boat is stationary.

Andaman 50

Which antifouling to choose?

Before making your choice, ask yourself the right questions:

• Your boat's maximum speed (≥ 25 knots)
• Can it be beached?
• Navigation frequency
• The type of environment with which the boat is confronted (marine or freshwater, currents, temperatures)
• The nature of your hull.

Erodible die :

• Destination : Sailing boats, not recommended for motorboats as the antifouling would erode too quickly. Composite, wood and steel hulls.
• Highlights :
  • No layering over time as the antifouling erodes.
  • Easy maintenance, no sanding before recoating.
  • Drag reduction.
• Weak points :
  • Not suitable for boats faster than 25 knots.
  • Uneven biocide emission depending on sailing frequency.
  • Soft coating that cannot withstand grounding.
  • Faster wear in high-current environments.

Hard Matrix:

• Destination : Motorboats/sailboats, composite, wood and steel hulls.
• Highlights :
  • Withstands high speeds.
  • Withstands environments with high currents.
  • Consistent biocide emission even when the boat is immobilized for long periods.
  • Withstands grounding.
• Weak points :
  • Higher maintenance, with mechanical intervention necessary to limit the multiplication of coats over the years (sanding).
  • Less efficient navigation.

Self-polishing matrix (Hydrolysis) :

• Destination: Sailboats (speeds under 25 knots), composite, wood and steel hulls.
• Highlight:
  • Constant biocide emission, regardless of the environment or how often the boat is sailed.
  • Light maintenance, equivalent to that of an erodible matrix.
  • Excellent sailing performance
• Weak point :
  • More expensive to buy.
  • Relatively soft matrix.

The choice of antifouling for a sailing catamaran needs to be carefully considered.

The self-polishing matrix is the most suitable for several reasons:

• Consistent effectiveness: It ensures a steady release of biocides, regardless of sailing frequency, which is ideal for sailboats that are not in constant motion.
• Sailing performance: Its performance is excellent, reducing drag for greater speed and energy savings.
• Simplified maintenance: Maintenance is light, with less need for sanding between applications, a significant advantage for catamaran owners.

However, it may not be suited to the requirements of a long-distance boat, being softer and less able to withstand grounding. In some parts of the world, it may be more difficult to obtain.

Lastly, the initial investment in a self-polishing matrix may be higher, but the benefits in terms of performance and long-term maintenance justify this choice, especially if the boat sails frequently or in environments with a high presence of biofouling.

A few words about sound antifoulings...

The field of sonic, or more precisely ultrasonic, antifoulings is an emerging, environmentally-friendly alternative to traditional antifoulings based on chemical biocides.

Ultrasonic antifouling :

Operating principle :

• Technology : Ultrasonic antifouling uses high-frequency sound waves, not audible to the human ear, to prevent or reduce biofouling on submerged boat surfaces.
   
• Mode of action : These ultrasonic waves create vibrations that disrupt the formation and adhesion of microscopic marine organisms, such as algae and shellfish larvae, preventing the formation of the initial biofilm that is the starting point for colonization.

Advantages :

• Ecologically Cleaner: Does not release chemicals into the water, reducing the environmental impact on marine life.
• Long life: Once installed, the system can operate without the need for annual renewal as with antifouling paints.
• Less maintenance: No need to refit to renew the antifouling, saving time and money.

Disadvantages :

• Installation: Transducers must be installed on the hull and properly secured to optimize wave diffusion.
• Variable efficiency : Efficiency may vary according to hull thickness and material, water salinity, and the presence of other sources of underwater noise.
• Power consumption : Although low, continuous power consumption is required to emit ultrasound.
• Initial cost : The initial investment to purchase and install the system can be significant.

Points to consider :

• Compatibility : This method is generally more effective on hulls made of solid materials such as polyester, aluminum or composite. It is less effective on wooden or ferro-cement hulls, which absorb vibrations.
• Use : Ideal for boats docked or moored for long periods, as it continues to operate even when the boat is not moving.
• Impact on marine life: Although ultrasound is not harmful to large marine animals, its effect on micro-organisms and plankton is still being studied.

Ultrasonic antifouling represents a promising solution for those seeking environmentally-friendly alternatives to chemical antifoulings.
However, it is not yet universally recognized as a complete solution, especially for high-speed boats or those requiring very specific maintenance.
 

It is advisable to combine this technology with other biofouling prevention methods, or to consider its effectiveness in the specific context of your boat and sailing area.

If you're considering this option, it's wise to carefully evaluate your boat's specifications, the regularity of your sailing, and perhaps consult feedback from other sailors or case studies to assess whether this technology meets your needs.