Box Coolers, Seachests & Pipework
Preventing bio-fouling in box coolers, sea chests and pipework is essential for ensuring that a vessel’s cooling system functions correctly. If fouling establishes in these locations, cooling capacity and flow rates can be severely reduced, which can lead to lengthy remedial work or even main equipment failure.
ICAF
Impressed Current Anti-Fouling (ICAF) systems are usually used to protect sea chests and the box cooler elements within. These elements are bathed in raw seawater as part of the cooling circuit for ships’ main engines or auxiliary power applications.
ICAF systems operate by passing a current through large anodes (usually copper) placed underneath the box cooler elements. The electrolytic process releases copper ions into the surrounding raw seawater, making the environment uninhabitable for algae, weeds and molluscs.
Pros
- These systems are widely available and are effective at controlling most kinds of marine bio-fouling.
Cons
- Fitting these systems requires cutting, welding and watertight wiring, which can involve extra Class surveys.
- The vessel also has to be dry-docked for the systems to be fitted or for the anodes to be replaced.
- The cooling seawater that passes through the sea chest is continually refreshed, so the expensive anodes need replacing regularly.
- They are not a zero-harm solution and rely on the poisonous effects of copper to kill organisms. This could soon put ICAF systems on the wrong side of tightening IMO biocide regulations.
Dosing systems
Dosing systems, like chemical dosing or electro-chlorination, can be used in box coolers but are more often used to keep transfer pipework clear of fouling or for flushing cooling systems. Regular dosing systems rely on chemicals like ferrous chloride, which prevents marine bio-fouling and also inhibits internal metal corrosion. In electro-chlorination systems, sea water is electrolysed using titanium cathodes and platinum-coated anodes. One of the by-products is chlorine, which acts as a biocide.
Pros
- These systems are also widely available and are effective at controlling fouling.
Cons
- Some dosing systems use less harmful chemicals like citric acid, but generally, these systems are not considered zero-harm.
- They are generally quite large and costly to maintain with other considerations like the storage of large volumes of liquid biocide and the safe venting of explosive hydrogen gas
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Sonihull uses ultrasound to stop fouling from settling on protected surfaces. Pulses of ultrasound in the range of 19.5 kHz to 55 kHz create microscopic ultrasound-induced non-inertial cavitation. This disrupts the first stages of the food chain without damaging the surface being protected.
The disruption further prevents the build-up of algae, slime and bigger more complex organisms on surfaces where bio-fouling is not wanted. The movement of water on the protected surface is also proven to prevent the adhesion of juvenile barnacle and mussel larvae
Pros
- These systems are easy to fit with no drydocking, cutting, drilling or welding required
- They can even be fitted whilst the vessel is in operation.
- With very low power consumption (3.6 Watts per transducer) these systems will even work when the vessel is idle in the water.
- It is also a zero harm system with no poisonous biocides or ablative microplastic pollution.
- Very low ongoing MRO costs compared to alternatives.
Cons
- Initial costs can be slightly higher than some MGPSs.
- Despite being an established antifouling technology in brewing, food processing and hydroponic farming industries, ultrasound has only recently started to gain a foothold in the more conservative shipping sectors.