What are some of the best practices for preventing marine biofouling on ship hulls?

Biofouling is heavily influenced by ship speed, water temperature, ship operating geography, roughness of the ship's hull surface, and the anti-fouling coating applied. For example, a ship that sits idle in warm tropic waters is likely to accumulate more marine growth than one traveling at speed in the cold waters near the poles. The surface roughness of the hull also affects the rate of growth, a very smooth hull makes it more difficult for critters to attach where as a rough hull makes it easier.

Pay attention to the sea water temperature that the paint manufacturers use to calculate the thickness of the vessels anti fouling coating. It is one of the most important factors and it is often overlooked.

"The first step to prevent marine biofouling" This statement is pretty misleading. Humans have been trying to prevent biofouling for a long time. What we might have learned is we haven't yet figured out how to prevent it, but we are learning how to mitigate the effects on what we put into the marine environment. Even the most toxic substances we had (and have since been banned) didn't prevent biofouling, but did significantly reduce the growth of biofouling. It appears that the path forward will include a large amount of educating industry members as well as regulators and the public.

Perhaps explore biological responses to this problem. Marine microbes and invertebrates that exhibit traits of bioactive molecules characterised by antifouling agents (primarily used as a defence mechanism against predators/bullies, to prevent fouling of their surfaces), environmentally "friendly" substances that don't have the same functional groups as those already banned, alternatives to chemical compounds that will not be regrettable substitutes, review of the technology/materials (R&D) around shipping hauls to prevent biofouling, improved technology to clean up biofouling and ensure capture of non-target species (no micro or nanoplastics used for cleaning ship hauls etc) in the event anti-biofouling techniques don't work successfully.

Biofilms containing proteins and bacteria allow more complex organisms to settle on a structure. Given that complex biofilm begins to coat most surfaces within hours of them being placed in the water, the most Important precaution is to stop these thin film “factories” containing proteins and bacteria from getting a grip. Old antifoul coatings did this by indiscriminately poisoning and could leach into harbour waters. A more targeted solution would be to develop localised enzyme releasing coatings that only affect the biofilm attempting to settle on the structure, but extensive research will be needed before any approval for open water trials. Controllable local chemical “warfare” is preferable to uncontrollable biological methods.

Also a consideration, but may be very difficult to predict, is the operational profile, as mentioned by David Hume. Some coatings are designed to release some biofouling at higher speeds. If a ship is purposely operating at speeds slower than what was designed to release fouling, then the ship is not realizing the foul release capabilities of the coating, but will be saving fuel. Not always easy to figure out which coating is best.

Graphite is a new promising material used as an anti fouling by Graphite Innovation and Technologies in Dartmouth,Nova Scotia, Canada 🇨🇦

Hull cleaning is at the top of the list of ways to manage fouling. Regardless of the best practices used, a ships' hull will accumulate enough fouling to affect fuel consumption. Cleaning a heavy slime coating can save 5% or more in fuel costs. Recent IMO studies show a 23% reduction in GHG emissions by keeping a clean hull. Hull cleaning robots are still a novelty but they have significant advantages over divers in safety, speed and efficiency. Until they are in more ports and getting more visibility, they will largely be under utilized. Educating ship operators, ports and regulatory groups about the changes to hull coatings (banned substances) and getting changes on in water hull cleaning prohibitions is a large part of the equation.

Large vessels may go three or more years between significant hull cleanings. One of the biggest drivers impacting the frequency of cleaning is the impact it has on fuel efficiency, a severely fouled hull on a ship may increase fuel consumption by close to 20%. Recently there have been a number of new technologies tried that leverage hull cleaning robots that reduce the cost and complexity of hull cleaning.

The idea of adding a biological control agent to the equation is terrifying to me. In my local waters it may be effective to some degree. But what happens when that agent is transported on the hull to another geographic location and the "organisms" attack the biology in the new region but it's locally important to that new region? So clean the hull before you go? Why not skip the step and just clean the hull and be done? Bioengineer a biofouling eating organism? So what else will it attack? Unintended consequences. Let's be sure we're not causing a bigger problem that what we are trying to manage. Frequent cleaning only requires scaling existing technology with service providers in many ports.

One way that a fouled hull is measured on board of a vessel is through a metric called 'slip' which is a percentage that signifies the difference between the actual distance travelled by a ship and the theoretical distance. Slip is measured daily by ships' engineers and a positive slip might be indicative of a fouled hull.

When I was studying Fish Biology at Scripps Institution of Oceanography in 1988, I suggested to Dr Rosenblatt that I thought there was merit in studying fish slime as a potential coating over the existing bottom paint to add greater time before marine growth could attatch when the topic of hagfish came up in his lecture. Later I learned that the US NAVY had the same idea and had created a synthetic hagfish slime. I would like to revisit this topic for use on my own vessel and to help reduce shipyard costs, and limit contamination to the environment.

I've seen various effective strategies against marine biofouling:- Anti-fouling Coatings- A vessel I worked on applied a silicon-based coating, significantly reducing fouling for over 18 months. Regular Dry Docking- A cargo ship I supervised had its hull cleaned biennially in dry dock, noticeably improving speed and fuel efficiency. Ultrasonic Anti-fouling Systems- On a luxury yacht, we installed ultrasonic systems, which proved effective in deterring organism growth. Speed Optimisation- A research vessel maintained higher speeds during transit, reducing fouling due to less idle time at sea.

It appears that the industry is largely having to relearn how to maintain hull effenciency as toxic hull coatings have been banned. As a hull cleaning service provider using ROVs, the biggest challenge has been changing the perception of in water hull cleaning not being allowed. This prohibition has been based on toxins in paints that are not typically present in current hull coatings. Ports and regulatory groups are starting to move to allow cleaning of micro fouling but the process is slow. The science behind continuous hull cleaning being effective is there, but there is still work to do on implementation.