Antifouling systems (AFS), whether a coating, a surface treatment or a device, are designed to protect the underwater hull from biofouling accumulation. Selecting and applying/installing the optimal system is key to achieving the best in-service performance results in terms of controlling biofouling. This not only protects the asset but also minimises the risk of transferring non-indigenous species and preserves marine biodiversity, an AFS function which is becoming significantly more important due to coordinated efforts to tackle biodiversity loss and an increased awareness regarding the gravity of the issue.
Selection and specifications
As awareness about the issues associated with biofouling grows, so do the attempts at solving them by increased levels of research and development of various AFS. Selecting the right AFS, whether a coating, treatment system, device or a combination of the above has never been more challenging as the market becomes more and more fragmented.
For the optimal solution to be identified, careful consideration needs to be given to a variety of vessel-specific factors affecting the suitability of potential AFS. The output of a methodical analysis of such factors is referred to as ‘functional specification’.
Examples of such factors are typical operational profiles and associated environmental parameters, expected activity and speed patterns, freshwater exposure, refit/new-build locations and AFS availability, substrate type, application/installation methods, biofouling management options and cleaning equipment availability at typical locations, etc.
The efficacy and performance of some systems may vary across areas of the underwater hull or may be affected by environmental parameters, such as temperature, water salinity and time spent in different ecological regions. This variability in AFS performance is a particularly important consideration for vessels, such as explorer yachts, that may be exposed to significantly different operational conditions over relatively short periods of time,
AFS installation and application
In terms of the underwater hull, once the optimal solution(s) have been identified, they need to be applied and/or installed in a manner ensuring that the systems’ expected in-service performance will not be compromised.
Coatings are the predominant technology used to protect the underwater hull from biofouling. Surface preparation, mixing and adequate application are also integral to the process.
Niche areas present different types of challenges in terms of application and installation considerations compared to the rest of the underwater hull. The guidance on recreational craft provides a non-exhaustive list of typical niche areas including the following:
• Propellers, thrusters and/or propulsion units
• Rudder stocks and hinges
• Rope guards, stern tube seals and propeller shafts
• Apertures or free flooding spaces
• Areas prone to anti-fouling damage from groundings
• Outlets, inlets, cooling pipes and grates
• Anchors, anchor wells, chains and chain lockers.
Some of these areas, such as the entrances to inlet and outlet discharge pipes, bow and stern thrusters, rope cutters and rudder fixtures may be neglected or inadequately protected when applying AFS. Other areas, such as anodes, are typically not coated. The guidance for recreational craft suggests that to minimise biofouling accumulation in the area, (1) the anodes can be flush-fitted, (2) the gap between the anode and the hull can be caulked or filled with a rubber backing pad, or (3) the area of the hull is coated with an AFS suitable for low water flow.
There are alternative AFS that could also be considered.
The international shipping industry is being encouraged to adopt a risk-based approach to biofouling management, a trend that will likely affect the recreational sector as well. As a response, the industry is adapting by using the power of predictive analytics to assess the risk of translocating non-indigenous, potentially invasive, species through digital tools. AFS maintenance is an important part of biofouling management. It is not unusual for yachts to be idle, which typically leads to biofouling accumulation. In-water hull cleaning is one of the common remedies in such cases. There are potential water quality and biosecurity related issues with in-water hull cleaning equipment not capable of capturing debris, therefore local requirements may be in place in different regions. Apart from capture capability, another consideration related to in-water hull cleaning is the AFS suitability. Some cleaning strategies or equipment may not be suitable for all types of coatings, treatment systems or devices.
Frequent cleaning or scrubbing of the surfaces, especially with equipment that may not be recommended for the purpose, could lead to early AFS failures due to issues with coating thickness or integrity.
Marine growth prevention systems, such as chemical injections in internal seawater systems, and any other devices and treatment systems designed for controlling biofouling accumulation should be regularly monitored according to manufacturer’s instructions.
Biofouling can have a detrimental effect not only on the operation of each vessel but also on the environment. Preserving marine biodiversity is crucial for achieving the UN Sustainability Development Goals and ensuring climate change resilience. The issue of translocating non-indigenous, potentially invasive, species via biofouling can be addressed through a coordinated effort on a global scale. Expert advice on developing an effective biofouling control strategy should be sought for best results.
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