Hulls & Surfaces
Fouling on a ship’s hull increases hydrodynamic drag and creates a corresponding spike in fuel consumption and exhaust gas emissions. The worse it gets, the more expensive it becomes to operate the ship.
Anti-Fouling Coating Systems
Since the global ban on tributyltin (TBT) in 2008, copper has become the biocide of choice in most anti-fouling paints, 95% of which still rely on biocides to kill organisms.
Copper is an effective poison for animal-based fouling (mussels, other molluscs, and barnacles). Typically, 20-50% by weight of all anti-fouling paint is copper or copper oxide. In order to control slime, algae and weeds, these coatings also need to be supplemented with booster biocides like Zinc pyrithione and Zineb. These are expensive, synthesised organic biocides and account for up to 5% by weight of current anti-fouling paint formulations.
- Coating systems are the most widely-available solution to hull fouling.
- They work well to reduce drag and improve vessel performance between drydocks.
- These coating systems rely on poisonous biocides which are being legislated out of the industry.
- Performance reduces over time and systems require regular drydocking and re-coating.
- The self-polishing nature of these coatings leaves a trail of microplastic particles and toxic chemicals in the oceans. Currently, an estimated 2,920 tonnes of microplastic pollution is released into the oceans annually, just from leisure boat coatings, in Europe alone.
Usually, an epoxy resin infused with a very fine powdered copper. sea-water attacks exposed particles of copper creating cuprous oxide, an effective biocide. Over time, this oxide further degrades into cupric hydrochloride which is eventually washed away by the movement of the vessel exposing fresh copper powder.
- Can work well in small leisure vessel applications and can last a long time.
- Copper is insulated by resin so electrolytic issues are avoided.
- Requires immaculate surface preparation, application and buffing which is difficult to achieve in large commercial shipping applications where fast coverage and waste minimisation is key.
- Still relies on copper as a biocide, so it is unlikely to pass the IMO’s MEPC zero-harm framework.
The use of ultrasound to prevent hull bio-fouling has been popular in the leisure boating sector for over a decade. In Norway, the Green Marina Project in cooperation with the World Wildlife Fund has recently proven that permanent antifouling can be achieved with just three elements: a hard hull coating, ultrasound systems to prevent macro fouling and regular use at high speed (or an in-water boatwash).
Until legislation removes existing biocide-based choices, scaling this approach up to the commercial shipping sector will remain slow. At the moment, the investment is prohibitive, but legislation to control invasive species and the financial pressures to maintain smooth hulls could provide the perfect environment for new systems to become more and more cost-effective.
- Sonihull’s ultrasonic technology provides proven effective protection against marine biofouling including algae, weeds, mussels and barnacles.
- Although ultrasound is already gaining favour as an anti-fouling solution in pipework systems and box coolers, full-scale hull protection is currently in trials.
- Ultrasound is unlikely to remove the need for some kind of hard coating on the hull.