Capture or no capture? How fouling rating decides the in-water cleaning method

What "capture" means

Cleaning with capture means collecting the material removed from the hull, the fouling organisms and any coating particles, rather than letting it drift into the water. Capture systems typically use a shroud or suction head around the cleaning tool, pumping the debris to the surface for filtering and disposal ashore.

Cleaning without capture, sometimes called open cleaning, releases everything into the surrounding water.

Why it matters

When divers remove macrofouling (weed, barnacles, tubeworms), they can release living organisms into a new environment. That is the main route by which marine species spread around the world on ships' hulls. Cleaning also abrades antifouling coatings, releasing biocide-laden particles. A port that allows open cleaning of heavy fouling is accepting both risks.

How the fouling rating decides the method

The IMO's 2023 Biofouling Guidelines rate fouling on a scale from no fouling, through microfouling (slime), to increasing levels of macrofouling. IMO's later guidance on in-water cleaning (MEPC.1/Circ.918) builds on that:

• Microfouling (slime) can usually be cleaned gently without capture, where the port permits, because it poses a lower biosecurity risk. This is often called proactive cleaning or grooming.
• Macrofouling should generally be removed with capture, and the captured material treated and disposed of properly.

The practical consequence: inspect first. Without a fouling rating, nobody can say which method is appropriate or whether the port will allow it.

What ports are doing

Port rules vary widely, and many are still evolving:

• Some allow in-water cleaning freely
• Some allow it only with an approved capture system
• Some allow only propeller polishing or work above the waterline
• Some publish lists of permitted cleaning companies
• Some do not allow it at all

The BIMCO and ICS industry standard on in-water cleaning with capture, with its approval procedure for cleaning companies, gives ports and owners a common reference, and more ports are expected to refer to it.

How Cleanship cleans

Our underwater hull cleaning is diver-operated brush cart and hand cleaning, with debris capture where the port requires it, and we document fouling and coating condition before and after. We tell you at quoting stage what the port requires for your vessel's likely fouling rating and what method we will use. See our underwater hull cleaning service and the complete guide to ship hull cleaning.

Questions to ask any contractor

1. Will you inspect and rate the fouling before cleaning?
2. Is your method with or without capture, and what system do you use?
3. What does the port require for this fouling level, and are you permitted to work there?
4. Where does captured debris go, and is there a disposal record?
5. How do you protect the coating?
6. What will the report show about fouling, method and coating condition?

A contractor who cannot answer these clearly is guessing.