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In-water hull cleaning means cleaning the underwater body while the ship stays afloat. It saves a dry-docking, but it has to be done carefully. The wrong tool can strip the coating and make the problem worse. This is how we approach in-water hull cleaning in Nagoya Port.
Before any cleaning starts, we ask what coating the ship has. Soft self-polishing paints, hard antifouling coatings and foul-release silicone coatings all respond differently. A brush that is fine for one can destroy another. The paint maker's guidance and the owner's instructions come first. If the coating condition is unknown, we begin with a test patch and examine it on camera before we continue.
Light slime can be removed with soft brushes or cloths by hand. For larger areas, a Diver-operated brush cart presses rotating brushes against the Hull and moves along it. For heavy barnacle fouling, stiffer brushes or scrapers can be used on suitable coatings. In some cases a small ROV with brushes works on the flat bottom. Whatever the method, the pressure and speed are kept within the limits that protect the paint.
Cleaning removes organisms and paint particles, and some ports restrict or control this. Rules differ by country, port and sometimes berth. Before we start, we ask the agent which requirements apply at the berth and plan the work to fit them. Where the rules or the owner's policy call for capturing the debris, we use methods that collect it, such as vacuum systems. If cleaning is not permitted at a certain location, we say so and suggest another way.
A brush cart can cover several hundred square metres per hour in light fouling, much less in heavy fouling. A full Hull of a 180 to 200 m ship normally takes 1 to 2 days with a team of divers. Partial cleaning of the flat bottom, the waterline or the propeller is faster.
We film the Hull before and after, and the report states the areas cleaned, the method, the condition of the coating and any damage found. If the cleaning exposes damage that was hidden, such as bare steel or a dented plate, we report it at once.
Hull cleaning means a Diver working close to the Hull for hours, often near sea chests and discharges. We make sure intakes are not running near him, that the propeller and thrusters are locked, and that the ship does not move without our knowledge. The surface supervisor logs each dive and keeps a standby Diver ready. If a ship needs to shift berth suddenly, we recall the divers at once.
After the job we provide a signed dive log, the cleaning report, and photographs. If a port or charterer asks for proof of the cleaning method or the debris handling, we can provide the details we have.
Q1. How fast can a brush cart clean a Hull?
A Diver-operated brush cart can cover several hundred square metres per hour in light fouling, and less in heavy fouling.
Q2. How long does it take to clean a whole ship in the water?
For a 180 to 200 m ship, usually 1 to 2 days with a team of divers, depending on fouling.
Q3. Can cleaning damage the antifouling coating?
Yes, if the tool is wrong for the paint. We check the coating type first, follow the maker’s guidance and begin with a test patch when in doubt.
Q4. Do local rules affect in-water cleaning?
Yes. Rules vary by country, port and berth. We confirm the requirements with the agent before work and use debris capture where required.
