Operational Guide · Registers & Logbooks

# Biofouling Management

Fewer invasive species transferred, less hydrodynamic resistance, fewer emissions: biofouling management is one of the rare environmental topics where ecological and economic interest coincide almost perfectly.

biofouling invasive species in-water cleaning GloFouling

## Operational Explanation

Biofouling (the accumulation of aquatic organisms on the hull and submerged surfaces of the ship) has been identified as one of the main pathways for transferring invasive aquatic species between different marine ecosystems, with significant impacts on biodiversity. The 2023 Guidelines for the control and management of ships' biofouling (adopted by MEPC 80 in July 2023) provide a globally consistent approach to biofouling management, replacing the previous 2011 guidelines.

In April 2025, the MEPC approved Guidance on in-water cleaning of ships' biofouling, to support the global availability of safe and environmentally responsible in-water cleaning services — a critical issue because in-water cleaning, if carried out without adequate containment, risks dispersing the very organisms and anti-fouling paint residues it is meant to remove. Also at MEPC 83 (April 2025), the IMO agreed to develop a legally binding framework for biofouling control and management, moving beyond the current voluntary nature of the guidelines.

Effective biofouling management also improves the hull's hydrodynamic performance, reducing fuel consumption and emissions, with a direct synergy with the CII rating.

## Regulatory Reference

2023 IMO Biofouling Guidelines (adopted with Res. MEPC.378(80), July 2023); Guidance on in-water cleaning approved in April 2025; development of a binding framework agreed at MEPC 83 (April 2025) is under way, though the guidelines currently remain voluntary.

## Scope of Application

Every ship, with particular attention to those with prolonged port stays or low speed, which favor the accumulation of biofouling on the hull, sea chests and propellers.

## Procedure / How to Complete It

1. Adopt a Ship-Specific Biofouling Management Plan documenting the prevention and management measures adopted per the 2023 Guidelines.
2. Periodically inspect the hull and critical submerged surfaces (sea chests, propellers) to detect biofouling accumulation, especially after prolonged port stays.
3. Before resorting to in-water cleaning, verify that the chosen service applies containment and residue capture systems per the Guidance approved in 2025.
4. Schedule hull and propeller cleaning in coordination with engine performance trend analysis, as an indirect indicator of hydrodynamic deterioration.
5. Monitor regulatory developments toward the binding framework under discussion since April 2025, to anticipate any transition from voluntary to mandatory requirements.

## Practical Example

Management example: a ship with a prolonged stay in a tropical port, a condition favoring rapid biofouling accumulation, schedules an underwater inspection at the next port call and, having detected significant accumulation, selects a certified in-water cleaning service with a containment and residue capture system compliant with the 2025 Guidance.

## Real Cases

The approval of the Guidance on in-water cleaning in April 2025 responds to a concrete concern: in-water cleaning carried out without adequate containment risks dispersing into the environment the very invasive organisms and anti-fouling paint residues the cleaning operation is meant to remove, defeating the environmental purpose of the intervention.

## Common Mistakes Mistake Library

Mistake | Consequence | How to avoid it
--- | --- | ---
In-water cleaning carried out by services without a containment and residue capture system | Dispersal of invasive organisms and anti-fouling paint residues into the environment | Always select in-water cleaning services compliant with the 2025 Guidance with adequate containment
No formal Ship-Specific Biofouling Management Plan in place | Non-systematic biofouling management, left to occasional interventions | Adopt a ship-specific management plan per the 2023 Guidelines
Engine performance deterioration not systematically linked to possible biofouling accumulation | Hull cleaning not scheduled promptly, with growing impact on consumption and emissions | Monitor engine performance trends as an indirect fouling indicator and schedule cleaning accordingly

## PSC Observations

The topic is not yet subject to standardized PSC verification given the voluntary nature of the current guidelines, but the evolution toward a binding framework agreed at MEPC 83 could change this scenario in upcoming regulatory cycles.

## Operational Tips

- Adopt a formal Ship-Specific Biofouling Management Plan, do not rely on unplanned occasional interventions.
- Always select in-water cleaning services with a containment system compliant with the 2025 Guidance, verifying credentials before every intervention.
- Link engine performance monitoring to hull/propeller cleaning scheduling, leveraging the synergy with energy efficiency.

## Checklist

- Ship-Specific Biofouling Management Plan adopted and updated
- Periodic inspections of hull, sea chests and propellers scheduled, especially after prolonged stays
- In-water cleaning services verified for compliance with the 2025 Guidance on containment and residue capture
- Engine performance trend monitored as a fouling indicator
- Developments toward the binding framework under discussion since 2025 monitored

## FAQ

Are the 2023 IMO Biofouling Guidelines mandatory?
No, they currently remain voluntary; however at MEPC 83 (April 2025) the IMO agreed to develop a legally binding framework, which could change this scenario in coming years.
Why does in-water cleaning of biofouling require specific Guidance?
Because if carried out without adequate containment it risks dispersing into the environment the very invasive organisms and anti-fouling paint residues the intervention is meant to remove, defeating its purpose; the Guidance approved in April 2025 supports the availability of safe and responsible services.
What is the relationship between biofouling management and energy efficiency?
Biofouling accumulation worsens the hull's hydrodynamic performance, increasing fuel consumption and emissions; effective biofouling management therefore also improves the ship's CII rating.
🎬 Additional photos, videos and interactive diagrams for this topic will be available in a future version of the platform.

## Related Topics

Ballast Water Management Convention In Depth Operational Energy Efficiency in the Engine Room

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