Biofouling is the one environmental issue that hits a ship twice. The marine growth that accumulates on a hull spreads invasive aquatic species between ecosystems — a major threat to ocean biodiversity — and at the same time it roughens the hull, driving up frictional resistance, fuel consumption, and greenhouse-gas emissions. That dual cost is why biofouling management has moved from good housekeeping to a regulated discipline. The IMO's revised 2023 Biofouling Guidelines, adopted as resolution MEPC.378(80), set a globally consistent, risk-based approach built on a ship-specific Biofouling Management Plan and a Biofouling Record Book, and a growing list of nations — Australia, New Zealand, Brazil, Norway — now enforce their own biofouling rules at the border, with ships ejected from waters and denied entry to ports for fouled hulls. A legally binding biofouling convention is now in development, with work beginning in 2026. For a superintendent or environmental officer, that means the hull's condition, the AFS, the inspection schedule, and the records behind them have become compliance-critical. This guide covers the IMO guidelines, the management plan and record book, inspection and the fouling rating, hull cleaning methods including in-water cleaning, and anti-fouling system compliance. To manage hull inspections, cleaning records, and the Biofouling Record Book in one system, book a Marine Inspection demo.
Green shipping · IMO MEPC.378(80)
Biofouling Management: IMO Guidelines & Hull Cleaning
A practical guide to the 2023 IMO Biofouling Guidelines — the management plan and record book, hull inspection and the fouling rating, in-water cleaning rules, and anti-fouling system compliance.
Invasive species
Hull fouling carries organisms between ecosystems — a major biodiversity threat
Fuel & emissions
A rough, fouled hull raises resistance, fuel burn, and GHG output
Why Biofouling Management Matters
The case for managing biofouling rests on the two impacts that the IMO guidelines exist to address. Both are significant, and together they make a clean hull both an environmental and a commercial priority. See hull management in a demo.
Invasive aquatic species
Organisms attached to a hull are carried to new environments, where they can disrupt ecosystems and biodiversity. This is the primary driver of the IMO guidelines and the coming convention.
Fuel and emissions
Fouling increases hull surface roughness, raising frictional resistance and therefore fuel consumption and greenhouse-gas emissions — so management is also an energy-efficiency tool.
Port access
Nations with sensitive ecosystems enforce biofouling rules at the border, and a fouled hull can mean ejection from waters, denied entry, and missed port calls.
Coming convention
The IMO has agreed to develop a legally binding biofouling convention, with work starting in 2026 and a draft framework expected around 2029.
The 2023 IMO Biofouling Guidelines
The revised guidelines, resolution MEPC.378(80), replaced the original 2011 version and introduced a more rigorous, risk-based framework. Understanding their core approach is the foundation of compliance. See compliance tracking in a demo.
Risk-based approach
Management is built around a ship-specific risk profile, with the anti-fouling system selected for the vessel's design, operating profile, and conditions.
Detailed documentation
A comprehensive Biofouling Management Plan and Biofouling Record Book are required, with far more ship-specific data than the previous guidelines.
Fouling rating scale
A rating scale assesses the extent of fouling in inspection areas, giving an objective trigger for cleaning and a record of hull condition.
Niche-area focus
Particular attention to niche areas — sea chests, gratings, rudder fittings, edges — which are especially susceptible to fouling growth.
The Management Plan and Record Book
Two documents anchor biofouling compliance, mirroring the structure of other MARPOL regimes: the plan that sets out how the ship will manage fouling, and the record book that proves it did. Both are increasingly demanded by port states.
Biofouling Management Plan (BFMP)
The officer or position responsible for implementing the plan
Details of the anti-fouling system installed and where
Inspection schedule and cleaning procedures
Contingency actions when fouling is identified
Biofouling Record Book (BFRB)
Retained on board for the life of the ship; physical or electronic
AFS and marine-growth-prevention-system maintenance records
In-water and dry-dock inspection and cleaning reports
Records of operation outside the normal profile
The BFMP is ship-specific and may draw on input from naval architects, shipbuilders, and AFS or marine-growth-prevention-system suppliers. The BFRB is the evidence trail: a complete, dated record of every inspection, cleaning, and maintenance action that a port state can examine to confirm the hull has been managed — and increasingly the document that decides whether a ship is granted access.
Inspection and the Fouling Rating
Inspection is the heartbeat of the risk-based approach, and the guidelines tie its frequency to whether the ship monitors its own performance. The fouling rating then turns each inspection into an objective decision. See inspection scheduling in a demo.
1
First inspection
For ships not undertaking performance monitoring, an inspection should be carried out within 12 months of the anti-fouling system's application.
2
Performance-triggered
Where performance monitoring — power and fuel-consumption trends — indicates the AFS is underperforming, an inspection should be triggered.
3
Ongoing cycle
Subsequent inspections should follow every 12 to 18 months, and possibly more often depending on the ship's risk profile and fouling.
4
Act on the rating
Where the fouling rating exceeds 1, indicating macrofouling, cleaning with capture is the recommended response, recorded in the BFRB.
Performance monitoring — tracking propulsion power and fuel consumption against expectation — is the early-warning system. A rising fuel trend often signals accumulating fouling before a hull inspection confirms it, which is why the guidelines treat performance data and physical inspection as complementary. The conclusions from every inspection should be recorded in the record book.
Keep the record book current
Track Hull Inspections, Cleaning, and the BFRB
The 2023 guidelines demand a complete Biofouling Record Book of inspections, cleaning reports, and AFS maintenance for the life of the ship. Marine Inspection schedules hull inspections by risk profile, logs cleaning and AFS maintenance with reports, and keeps the BFRB current and ready for any port-state check. Book a 30-minute demo to see biofouling record-keeping, or start a free trial today.
Hull Cleaning Methods
When inspection shows cleaning is needed, the method matters — for the hull, the coating, and the environment. The guidelines distinguish proactive from reactive cleaning and set expectations for how cleaning is done. See cleaning records in a demo.
Proactive cleaning
Periodic removal of microfouling to prevent macrofouling taking hold, done in line with the AFS provider's recommendations so as not to damage the coating.
Reactive cleaning
Removal of established fouling identified at inspection. Delaying it when inspection shows it is needed increases the risk of spreading organisms.
Cleaning with capture
Where the fouling rating exceeds 1, capturing the removed material is recommended to prevent release of organisms and waste substances into the water.
Dry-dock cleaning
Full hull cleaning and AFS renewal at dry-docking, the most thorough option, with wastewater contained and treated ashore.
In-Water Cleaning Rules
In-water cleaning is valuable — it removes fouling without dry-docking — but it carries risks the IMO addresses in dedicated guidance (MEPC.1/Circ.918). It can damage coatings and release harmful waste substances and organisms, so it is tightly conditioned.
Protect the coating
Cleaning should avoid unnecessary wear or damage to the anti-fouling coating, as harsh removal can compromise its remaining service life.
Minimise waste release
Release of waste substances — biocides, metals, microplastics, removed fouling — must be minimised, with capture where the fouling level requires it.
Local approval
Cleaning must conform to local regulations and approvals; many ports require advance notice — Brazil, for example, asks for a request 10 days before arrival.
Record the result
A cleaning report verifying the hull's condition should be produced by the service provider and recorded in the Biofouling Record Book.
The tension at the heart of in-water cleaning is that the same operation that restores hull efficiency can, done badly, damage the coating and pollute the water. The coming biofouling convention is expected, among other things, to help standardise in-water cleaning approvals so ships can access it in more places than today.
Anti-Fouling System Compliance
The anti-fouling system is the first line of defence, and it is regulated separately under the AFS Convention, which controls the biocides a coating may contain. Keeping the AFS both effective and compliant is central to biofouling management.
The AFS Convention
The 2001 Convention on the Control of Harmful Anti-Fouling Systems bans harmful organotin compounds such as TBT and controls other harmful biocides in coatings.
The cybutryne ban
Cybutryne was added to the Convention from 1 January 2023; coatings containing it must be removed or sealed at the next AFS renewal, and within 60 months of application.
Right system for the profile
Different AFS suit different operating speeds and niche areas, so the system should be selected on technical advice for the specific ship and its trade.
Maintain coverage
Adequate coating thickness and touch-up on edges, welds, and niche areas keep the AFS effective where fouling pressure is highest.
The thread tying the whole regime together is the record. Biofouling compliance is proven by a ship-specific plan, a complete record book of inspections and cleaning, an effective and compliant anti-fouling system, and performance data showing the hull is managed. A ship that inspects on schedule, cleans responsibly, and documents it all turns a port-state biofouling check into a routine — and keeps its hull efficient, cutting fuel and emissions as a direct bonus. Book a demo to see biofouling compliance management.
Frequently Asked Questions
What is biofouling management?
Biofouling management is the control of marine growth on a ship's hull and niche areas to minimise the transfer of invasive aquatic species and to keep the hull efficient. It follows the IMO's 2023 Biofouling Guidelines through a ship-specific Biofouling Management Plan, a Biofouling Record Book, an effective anti-fouling system, regular inspection, and responsible cleaning.
What are the 2023 IMO Biofouling Guidelines?
They are resolution MEPC.378(80), adopted in July 2023, replacing the 2011 guidelines. They introduce a risk-based approach with ship-specific risk profiles, more detailed documentation through the BFMP and BFRB, a fouling rating scale, and a focus on niche areas, aiming for a globally consistent approach to minimising invasive-species transfer through hull fouling.
Is biofouling management mandatory?
The IMO guidelines are currently recommendatory, but several nations — Australia, New Zealand, Brazil, Norway — enforce their own mandatory biofouling rules, with ships ejected or denied entry for fouled hulls. A legally binding IMO biofouling convention is now in development, with work starting in 2026 and a draft framework expected around 2029.
How often should a hull be inspected for biofouling?
For ships not undertaking performance monitoring, the first inspection should be within 12 months of anti-fouling system application, with subsequent inspections every 12 to 18 months and possibly more often. Where performance monitoring shows the AFS underperforming, an inspection should be triggered. The fouling rating from each inspection determines whether cleaning is needed.
What are the rules for in-water cleaning?
In-water cleaning, covered by IMO guidance MEPC.1/Circ.918, must avoid damaging the coating, minimise release of waste substances, capture removed material where the fouling level requires it, and conform to local regulations and approvals. Many ports require advance notice — Brazil, for example, asks for a request 10 days before arrival — and the cleaning result must be recorded in the BFRB.
What is the AFS Convention and the cybutryne ban?
The AFS Convention (2001) controls harmful anti-fouling systems, banning organotin compounds such as TBT. Cybutryne was added from 1 January 2023; anti-fouling coatings containing it must be removed or over-coated with a sealer at the next AFS renewal, and at the latest within 60 months of the cybutryne coating's application.
Built for biofouling compliance
A Clean Hull, a Complete Record, an Open Port
Schedule hull inspections by risk profile, log fouling ratings, cleaning reports, and AFS maintenance, keep the Biofouling Record Book current for the life of the ship, and tie it to fuel-performance data — so port-state checks are routine and the hull stays efficient. Marine Inspection keeps biofouling managed and documented. Book a tailored walkthrough or start a free trial today.
