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Hull cleaning and biofouling: a little-known market

By Arthur More · professional saturation diver · 23 August 2026

Published 30 July 2026 · 8 min read · 1,543 words

In brief

Cleaning a ship's hull underwater is one of the steadiest jobs in port-based commercial diving. Biofouling — marine life that attaches to the hull — increases fuel consumption and carries invasive species, so its management is increasingly regulated. It's a low-profile market, highly repetitive, with steady demand.

The commercial diving that shows up in features is the platforms and the saturation vessels. The kind that keeps many small companies around the world afloat is different: cleaning hulls, inspecting propellers, and scraping off the marine life that attaches itself to ships. It's low-profile, repetitive, and its demand never stops.

What biofouling is and why it matters

A submerged hull starts getting colonised within days. First a bacterial biofilm appears, then algae, and on top of those, hard organisms settle in: barnacles, mussels, tube worms, bryozoans. That whole mix is called biofouling.

The direct effect is hydrodynamic. A rough hull creates more drag, and that drag is paid for in fuel. For a shipowner, the difference between a clean hull and a colonised one shows up in consumption, emissions and operating cost over thousands of miles. That's why cleaning isn't a cosmetic matter, it's an economic one.

The second effect is environmental, and it has grown in importance over recent years. A hull acts as a carrier: organisms that attach in one port can detach in another, thousands of kilometres away, and establish themselves where they never existed before. Introducing invasive species this way is a recognised marine biosecurity problem, and the regulatory response has been growing.

The regulatory framework, in essence

Biofouling management has gone from being a shipowner's own decision to being shaped by rules at several levels. The International Maritime Organization has developed guidelines for the control and management of ships' biofouling to reduce the transfer of invasive aquatic species, and several countries have added their own requirements for entering their waters.

In parallel, many port authorities regulate in-water cleaning within their jurisdiction. The concern is twofold: on one hand, the organisms that come off; on the other, the antifouling paint debris, which contains biocides and shouldn't end up in the port's sediment. Hence the growing trend of requiring systems to capture and filter the waste generated during cleaning.

For the diver, the practical consequence is that the job comes with paperwork: permits, approved procedures, a record of what was done and, increasingly, documented proof that the waste was managed properly. Working without that exposes both the company and the client to penalties.

How the work is done

Prior inspection

Before cleaning, an assessment is made: type and condition of the coating, degree of colonisation, critical zones. So-called niche areas — sea chests, chain lockers, rudder, propeller shaft struts, propeller — concentrate the problem because they're hard to protect with paint and hard to clean. Much of the inspection is documented on video for the shipowner.

Limpieza

The usual methods are:

Mechanical brushing: units with rotating brushes, either handheld or mounted on carts, suited to heavy, consolidated fouling.
Cavitation: equipment that dislodges fouling through the implosion of microbubbles, gentler on the coating.
Pressure water jetting, effective but high-risk for the operator, and more likely to damage the paint if not set correctly.
Sistemas robotizados Cleaning robots controlled from the surface, with integrated capture and filtering, increasingly common for environmental and safety reasons.

The choice isn't free: it depends on the type of coating. A self-polishing paint or a low-friction silicone coating gets damaged by aggressive brushing, and damaging the coating speeds up recolonisation, so the cure ends up worse than the disease.

Propeller and critical items

Propeller polishing is handled separately. A rough propeller hurts propulsive performance out of all proportion to its surface area, so it's usually treated as a service in its own right, with demanding finish standards.

Specific risks

The depth is shallow, but the job has its own well-identified hazards:

Isolating the ship's energy sources: before entering the water, written confirmation is required that the propulsion, rudder, bow thrusters and sea chests are locked out. This is the single most critical point of the whole operation.
Suction from sea chests, capable of trapping a diver against the grating.
Port traffic: movements of other vessels, tugs and support craft in the same basin.
Near-zero visibility Reduced visibility, in many ports, with the work done almost entirely by feel.
Umbilical snagging on the ship's structure and on the cleaning unit itself.
Water quality: chemical and biological contamination that calls for proper protection and strict decontamination of the equipment.

None of this is exotic, and that's exactly why the real risk is routine. The typical accident in this line of work doesn't happen on the difficult manoeuvre, it happens on the two-hundredth time doing the same one.

What the market looks like

It's a local market, made up of small and medium companies tied to specific ports, with recurring clients: shipowners, agents, shipping lines. The work is organised around short port calls, with near-constant availability required, because cleaning happens while the ship is stopped, and that window doesn't wait.

Rates are noticeably lower than the offshore work covered in how much a diver earns, and the pace makes up for it with volume and continuity. For many professionals it's the stable base they live off between campaigns.

As an entry point it has a clear advantage: it builds up logged hours and teaches the discipline of working under supervision and procedures. It doesn't replace offshore experience and on its own it won't open the door to saturation diving, but it's real work from day one, which is something in short supply when starting out, as we cover in how to get your first job as an offshore diver.

If you want to place this niche within the wider industry, you'll find the rest of the picture in companies and in empleo and in equipment you'll find the equipment associated with this kind of work.

A trend worth watching

Tightening environmental rules are reshaping this niche. Cleaning without waste capture has its days numbered in many ports, and that favours companies able to invest in filtering systems and robotic units.

For the diver, the takeaway isn't that the work disappears, but that it changes: less brush in hand and more equipment handling, procedure control, documentation and inspection. It's the same direction seen across the rest of the industry, and reading it in time usually makes the difference between a long career and an interrupted one.

Inspection: the service that comes with cleaning

Cleaning almost never happens without inspection. While the diver works the hull, they document the condition of the coating, the sacrificial anodes, the sea chests and any visible welds, usually with video and referenced photography.

That material has its own value for the shipowner, who uses it to plan maintenance and to demonstrate the ship's condition to third parties. In some cases in-water surveys recognised by classification societies are also carried out, which require divers and inspectors with specific qualifications and approved procedures.

It's the natural specialisation path within this niche: moving from cleaning to qualified inspection, through underwater inspection and NDT training like the kind we describe in underwater inspection diver. It changes the type of work, the rate, and the physical toll, which in a trade like this ends up mattering.

Frequently asked questions

What is biofouling?

It's the build-up of marine organisms — biofilm, algae, barnacles, mussels, bryozoans — on the submerged surfaces of a ship or a structure. It increases hull roughness, drag, and with it, fuel consumption.

Why is it cleaned underwater rather than in dry dock?

Because putting a ship in dry dock is expensive and takes it out of service. In-water cleaning recovers hull performance during a port call without interrupting operations, though it doesn't replace dry maintenance.

Is hull cleaning allowed in every port?

No. More and more port authorities restrict or place conditions on in-water cleaning, and usually require waste capture systems to avoid releasing organisms and antifouling paint debris into the environment.

What's the connection to invasive species?

The hull acts as a transport vector: organisms attached in one port can detach in another thousands of kilometres away. That's why biofouling management has become a matter of marine biosecurity, not just efficiency.

What equipment is used?

Everything from handheld brushes and cavitation equipment to rotary brush units and, increasingly, cleaning robots controlled from the surface. The choice depends on the type of coating and the port's environmental restrictions.

Is it a good job to start out in commercial diving?

It's one of the most accessible entry routes in the port sector, with shallow dives and steady work. It doesn't give saturation experience, but it does give logged hours, operational routine, and contact with companies in the industry.

Published 23 August 2026 · By Arthur More, professional saturation diver

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