Reducing biofouling build-up on non-trading vessels

The 'National biofouling management guidance for non-trading vessels' recommends cleaning and maintenance practices that will minimise biofouling on all non-trading vessels. These are summarised below.

Many vessel types in this sector have specific operating characteristics that lead to individual vessels posing a higher risk of spreading marine pests. Operators should refer to the 'National biofouling management guidance for non-trading vessels' PDF Icon  PDF [1.83mb] for guidance on specific maintenance practices for particular vessel types.

The key maintenance actions to reduce the risk of non-trading vessels spreading marine pests include:

  • slipping or drydocking vessels before relocation to thoroughly clean to remove biofouling and to repair/replace the antifouling coating
  • conducting an in-water inspection and where necessary, removing the vessel from the water to be cleaned or completing an in-water clean (noting the latest guidance for in-water cleaning in Australia)
  • inspecting internal seawater systems, cleaning strainer boxes and dosing or flushing of these systems
  • inspecting and cleaning all above water equipment and areas that may accumulate sediments and biofouling.

Slipping and drydocking

Tug at drydock for scheduled maintenance


Schedule maintenance to repair or renew the vessel’s antifouling system at intervals within the projected life of the coating system.

Make sure that the facility is licenced and has adequate waste management facilities to capture and dispose of removed biofouling. 


Vessel cleaning

Improve the effectiveness of hull cleaning by paying particular attention to niche areas.

  • Clean any gap between a fitting and the hull such as behind sacrificial anodes and stabilisers.
  • Extend all retractable equipment, and thoroughly clean all fittings (such as thrusters and dredge ladders and any associated housings or voids).
  • Clean sea chests, ensuring that any detached biofouling debris is removed.
  • Clean internal niches around shafts and propellers and nozzles (such as stern tubes, shaft couplings, rope guards and bearings, and rudder hinges).
  • Clean other voids and niches, particularly apertures and orifices (such as small bore intakes and outlets).

bow thruster with mussels


Mussels can be seen accumulating on this bow thruster housing.

   Image courtesy of Cawthron Institute

Open sea chest showing biofouling


Sea chest showing heavy biofouling accumulating around the opening.

   Image courtesy of Cawthron Institute

Sacrificial anode 

The space behind this sacrificial anode needs thorough cleaning at each drydocking




Applying antifouling

Choosing the correct antifouling coating is crucial to reducing biofouling build-up. Include each of the following practices:

  • Inspect antifouling coatings and repair any damaged areas even if coating replacement isn’t scheduled for that docking.
  • Work closely with your antifouling supplier to identify the most appropriate coating(s) for the operating profile of your vessel, taking into account maximum and typical operating speeds, duration and frequency of periods of inactivity and maintenance and docking cycles.
  • Consider applying different coatings to different areas of the vessel to match performance and longevity requirements with wear and water flow. This is particularly so in either high wear areas such as the bow area or rudder or low flow areas such as sea chest interiors.
  • Apply coatings to the accessible inner portions of intake/outlet ports.
  • Consider coating areas not normally treated such as main and thruster (auxiliary) propellers and log prober. Consult your antifouling coating supplier for advice.


  • Tributyltin (TBT) based coatings can no longer be used in Australia or worldwide.
  • Coatings containing biocides must be registered by the Australian Pesticides and Veterinary Medicines Authority.

In-water inspections

In-water inspections should be undertaken:

  • routinely, to monitor biofouling build-up 
  • to assess the biofouling risk prior to relocating.

Use qualified and experienced divers familiar with biofouling and marine pest risks to undertake in-water inspections.

Where inspections detect a build-up of biofouling, remove it prior to moving to another location by either removing the vessel from the water for cleaning or by undertaking an in water clean (noting the latest guidelines that apply to in-water cleaning in Australia).

Inspect and maintain internal seawater systems

Regularly inspect internal seawater systems for biofouling accumulation and periodically flush with freshwater or treat using thermal or chemical dosing. If using chemical treatments, ensure that the chemical is compatible with pipework configurations, components and materials and complies with local regulations.