Hull Cleaning and Biofouling

The international guidance on ship biofouling

The International Maritime Organization revised its guidance on controlling ships' biofouling, and the Marine Environment Protection Committee adopted the new 2023 Guidelines at its eightieth session in July 2023, as resolution MEPC.378(80). The IMO says the revision aimed to improve the uptake and effectiveness of the earlier 2011 text, which was written to minimise the transfer of invasive aquatic species. For a robot buyer, the point is that cleaning sits inside a planned management routine for the ship, so the vehicle is one tool in a documented process rather than a one-off fix. Ask how each cleaning job will be recorded and who will keep those records.

When cleaning in the water is acceptable

The Anti-fouling and in-water cleaning guidelines published by Australia and New Zealand in June 2013 start from a clear preference: where it is operationally and economically practicable, vessels should be cleaned out of the water. When in-water cleaning does go ahead, the coating must be suitable, the method must not damage it and discharges must meet local standards. For macrofouling picked up overseas, the guidelines expect the method to aim to capture debris greater than 50 micrometres in diameter. Microfouling may be removed without full containment if the method follows the coating maker's advice. Those distinctions decide whether a simple brush crawler is enough or whether you need capture and filtration.

Getting approval before a robot goes in

Permission is local. A page from Australia's Department of Agriculture, Fisheries and Forestry describes the approval process for in-water cleaning in Australian waters as complex, with responsibility shared between government agencies and port authorities and procedures that vary by location. It advises vessel operators to contact state and territory authorities well before any planned cleaning. A national review has also been under way, with an exposure draft of new guidelines that closed for public comment on 1 March 2025, so check which version a port applies. Build that lead time into port schedules, and expect to be asked what the robot captures, where the waste goes and who will operate it.

Questions for a hull-cleaning robot supplier

Start with the fouling you actually have. Light slime on a well-kept coating calls for gentle, frequent grooming, while established growth needs a method that can remove it and contain what comes off. Ask the supplier how the robot captures debris, how fine its filtration is and how the waste is handled ashore. Check which coatings it has been tested on and how it avoids scratching them. The Australian guidance treats propeller polishing and the cleaning of niche areas as in-water cleaning too, so ask how those areas will be handled, whether by the robot, a diver or a separate tool. Finally, request before-and-after footage from a real job, with position and time recorded.

Sources and further reading

• 2023 IMO Biofouling Guidelines (resolution MEPC.378(80)) — International Maritime Organization.
  IMO guidance on managing ships' hull fouling, including biofouling management plans and records of hull cleaning.
• Anti-fouling and in-water cleaning guidelines — Department of Agriculture, Fisheries and Forestry (Australian Government).
  Why in-water cleaning is controlled in Australia, who approves it and the status of the draft replacement guidelines.
• Anti-fouling and in-water cleaning guidelines (June 2013) — Australian Department of Agriculture, Fisheries and Forestry and New Zealand Ministry for Primary Industries.
  Joint guidelines with a decision tool for when in-water cleaning is acceptable and how much debris must be captured.

Common questions

What is the difference between hull grooming and hull cleaning?

Grooming is light, frequent work that keeps a hull free of early slime so larger organisms struggle to settle. Cleaning usually means removing growth that is already established, which releases more material and is more likely to need capture equipment and a port's permission.

Can I clean a yacht hull in the water myself?

It depends on where you are. The IMO has separate Guidance for minimizing the transfer of invasive aquatic species as biofouling (hull fouling) for recreational craft, MEPC.1/Circ.792, and marinas may set their own rules. Ask the harbour office before you start.