Managing biofouling on petroleum vessels

To minimise biofouling, the following practices are recommended:

  • Slip or drydock vessels before relocating to thoroughly clean the hull and niche areas, remove all biofouling and repair/replace the antifouling coating.
  • Conduct an in-water inspection and where necessary, undertake drydocking, slipping or an in-water clean where regulations permit, noting the latest guidelines for in-water cleaning in Australia.
  • Inspect internal seawater systems, clean strainer boxes and dose or flush these systems.
  • Inspect and clean all equipment (above and below water) and areas that may accumulate sediments and biofouling.

Slipping and drydocking

Schedule regular biofouling removal from the vessel at an on-shore facility that 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 as follows:

  • 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).
  • Open up and 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 clearly 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 and applying it correctly is crucial to reducing biofouling build-up. Include each of the following steps:

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