KC Maritime Consultancy Ltd.

Biofouling is the process of aquatic organisms such as bacteria, diatoms, algae, barnacles, mussels, tubeworms, etc. attaching to ships’ hulls or any other submerged, or semi-submerged structure.

The process occurs in stages, from a conditioning layer through slime layer to barnacles; but even at an early stage when only a slime layer exists, it increases ship hull roughness and hence its resistance to movement through the water.

Prevention of biofouling is achieved mostly through the use of antifouling paint. Both ancient and modern efforts in producing an effective antifouling paint had one thing in common: toxicity to marine life.

The ancient story of biofouling and antifouling

One of the early records on the detrimental effect of biofouling on ships’ speed was the reference to Echeneis remora; a fish mentioned by the Greek philosopher Aristotle in the 4th century B.C. The fish would attach itself to the ship’s bottom by means of a sucking disk on top of its head, and Aristotle credited it with the ability to “slow down ships going at full speed, or even stop them entirely as if they were tied to one spot in the ocean”.

A few hundred years later, another Greek philosopher Plutarch stated that “fouling, rather than the Echeneis might be responsible…” He also stated that “it was usual to scrape the weeds, ooze, and filth from the ships’ sides to make them go more easily through the water”.

Wooden ships of ancient times were protected by wax, tar, arsenic and sulfur mixed with oil, lead and copper sheathing. Some had a purpose of protecting the hull from shipworm, some for water-tightness, and protection against biofouling.

Attempts to prevent biofouling went on throughout the centuries. Many antifouling paints had been tried and failed and most of them used toxins such as copper, mercury, and arsenic with various compounds.

All efforts towards the production of an effective antifouling paint proved “useless or worse”.

It wasn’t until the 18th century that copper sheathing was recognized as having outstanding antifouling properties, causing the interest in the development of antifouling paints to fade.

However, with the onset of iron ships in the 19th century, copper sheathing was abandoned due to its corrosive effect on iron (galvanic corrosion) and its excessive rate of wear.

In those days, biofouling even proved useful; in 1862, the copper sheathed H.M.S. Triton “had her plates corroded to such paper thinness that, according to her commander, she was only kept from foundering by her fouling; practically sailing home on her barnacles”.

The 20th century developments

It wasn’t before the early 20th century that the study of slimes led to two important results: apparent relation between slime formation and biofouling and development of techniques for measuring the rate at which toxicants used were given off by the paint surface.

Further experiments on controlling the rate of discharge of toxicant from the paint surface led to the introduction and widespread use of tributyltin (TBT) paint in the 1960s’.

TBT paint applied to hull leached toxicants which prevented the settlement of marine organisms. TBT and its variant, the self-polishing paint were a success.

However, some twenty years later, the much-celebrated TBT paint proved detrimental to marine life. It had an adverse effect on certain marine species, also causing a condition known as imposex – imposed sexual organ found in rock shells, some other deformities in shellfish, deaths of certain marine mammals, and the weakening of fish immunological systems.

 As a result, the IMO banned its use in 2003, with a complete prohibition by 2008.

 Since the TBT ban, different antifouling systems have been designed, biocide-free or not, each of them exhibiting problems such as the overall cost of hull maintenance, poor self-polishing including little activity during idle times, effectiveness only at certain ship speeds, etc.

 The sheer volume of paint types left shipowners and operators with numerous alternatives to hull coatings of varying prices and features, along with the demanding task of optimising fuel consumption and contemporary environmental protection compliance.

The 21st century biofouling issue

While in ancient times the main concern related to biofouling was ship speed, in the modern era it is also the transfer of invasive species and greenhouse gas emissions.

And yet, no antifouling system to date has been successful in combating biofouling without causing harm to the marine environment.

At the COP26 side event held on 4th November 2021 (Managing Biofouling – A Win-Win Solution to Help Curb Climate Change and Preserve Ocean Biodiversity), it was mentioned that “the perceived impact of biofouling is likely to have been historically underestimated by industry leaders and policy makers”.

This “underestimation” referred to the greenhouse gas emissions strategy, but there is so much more than meets the eye when it comes to biofouling management, which is by no means a simple task.

As many times before, there are again newly available options, such as bio-repellent paint, and ultrasonic biofouling repellant.

Despite claims for being “green” and perfectly harmless to the marine environment, chances are that some of the new antifouling systems will likely prove detrimental to one sea-dwelling creature or another at some point.

The ultrasonic antifouling system, for example, works in a way that the ultrasonic sound waves emitted through the hull generate a barrier of moving water molecules throughout the submerged hull area which targeted micro-organisms cannot survive. 

If they cannot survive, then it is not just a repellent as claimed. Still, killing some is presumably better than poisoning all, but the lack of clarity on the matter does give the overall impression that technology continues working against nature.

One example of the detrimental effect of technology is naval sonar which has been known to cause whales to beach and die in agony in some parts of the Mediterranean from the 1960s’ on. And yet, it was only in 2019 that scientists understood why. Whales committing suicide in other parts of the world remains a mystery…

Perhaps checking various ship tracking maps cluttered with ships could shed some light on it.

One can argue that all the efforts to preserve ocean biodiversity are still too little, but, is it also too late?