Transformational technology has come to the seemingly mundane business of anti-fouling – the perennial bugbear of the shipping industry.
Time consuming, expensive, exceedingly complex but unavoidable, anti-fouling traditionally required divers to be sent down to assess the state of the hull.
Now, help is at hand in the form of digitally controlled devices such as Hempel’s remotely operated vehicles (ROVs) that can be deployed to inspect hulls in as little as two hours, searching for bio-fouling or coating defects. The resulting high-resolution video footage can be analysed in real time by algorithms.
“Our experts use classification systems aligned with international standards, such as those produced by the National Association of Corrosion Engineers (NACE) and the Baltic and International Maritime Council (BIMCO), to make an assessment of the bio-fouling type and coverage over the entire wetted surface of the hull,” Hempel group segment manager for marine drydock Andreas Glud tells Container Shipping & Trade in a briefing.
And the HullSkater, a device with magnetic wheels developed by Jotun and Kongsberg, works its way around the hull removing bacteria and bio-film before they can accumulate to levels that lead to speed loss.
And that is to be avoided at all costs. According to Hempel’s definition, speed loss is all about hydrodynamic inefficiency. “If a vessel’s main engine is set at a specific power output, it will propel the ship at a constant speed through the water.”
But that is before the hull becomes fouled. “The accumulation of fouling will happen over time, increasing drag and decreasing the vessel’s speed in spite of a constant output of power by the main engine. This reduction in speed is termed ‘speed loss’,” Hempel explains.
However, instead of ships trailing around a wide variety of unwanted sea life for months on end, the latest coating technology claims to keep hulls cleaner for longer. And there is a lot of unwanted sea life out there.
Technically speaking, notes Mr Glud, the most common forms of bio-fouling comprise slime (microscopic organisms including bacteria and diatoms); incipient algae (adherent algae at the early stage of its formation of about 5 mm in length); algae (soft biofouling between 3 mm-5 mm in length); long algae (soft biofouling longer than 3 cm); small calcareous (hard biofouling under 5 mm such as barnacles, mussels and tube worms; and large calcareous (hard biofouling bigger than 5 mm including barnacles, mussels and tube worms).
The way these organisms accumulate closely reflects the operational pattern of the vessel, explains Mr Glud. “The intensity of fouling depends on a range of factors including the water temperature, nutrients, light and the vessel speed. Algae growth is very dependent on light and will typically settle on the vertical sides of the ship, closer to the waterline. While barnacles and tubeworms are more likely to attach to any cavities and the flat bottom. A vessel sailing in warm waters with higher levels of nutrients – closer to the shore, sailing at low speeds or even idle – will have faster fouling growth, for example.”