Biofouling

General fouling is the undesirable accumulation of solids on rigid interfaces. In shipbuilding, is referred to as fouling by sessile organisms or fouling the colonization of ship hulls or other immersed in water structures. These organisms are especially shellfish such as mussels and barnacles as representatives of the barnacles and goose barnacles.

Effect

The organisms are able to keep themselves on very smooth surfaces. They can not be solved by massive mechanical stress. In the case of the aforementioned crustaceans ensures a basal disc, which induces a very strong suction effect due to the resulting negative pressure at the surface. Mussels hold on by a strong adhesive that sticks to itself teflon and it ensures very good grip. The chemical structure of this substance was elucidated at the beginning of 2004. It is the amino acid used in the treatment of Parkinson's disease 3,4- dihydroxyphenylalanine ( levodopa), which is bound by a Fe3 ion in an octahedral complex in the adhesive. In this way, a network that forms the byssus threads of the shell forms.

Damage and countermeasures

In the case of fouling on ship hulls gives an economic loss to the owners and users of the ship. By the fouling takes the ship to put on weight, and he at the same time increases the flow resistance, which leads to slower speeds or higher fuel costs; Also the hull can be damaged.

To counteract fouling, especially so-called anti-fouling paints have been used in the recent past. They should act with poisons ( primarily heavy metals, such as tributyltin hydride / TBT) against the organisms. These substances are, however, now largely banned and taken off the market because the toxins escape into the water, accumulate in the sediment, resulting in considerable heavy metal pollution of the seas. Thus, underwater coatings were banned based on tin with the EU Regulation 782/2003. A ban on the use of copper-containing paints is provided. As a replacement for tributyltin today various other biocides are used. The most important are DCMU ( a urea derivative) Cybutryn ( a triazine ) Dichloroctylisothiazolinon (Sea- Nine 211, an isothiazolinone ) and copper and zinc pyrithione. Connected is the use of biocides with SPC systems (Self Polishing Copolymer), which cause a constant Biozidfreisetzung a permanent polishing rate.

Recent developments in the field of anti-fouling systems are based on silicones, the so-called Silicon FRC (Silicone Fouling Release Coatings ). These systems are characterized by an extremely smooth surface, to a large extent flexible, cold- resistant, non- eroding and sea water resistant properties with a high service life. A relatively new method against fouling proceed comes from the Materials Research. The skin of sharks has been studied, as it is not attacked by parasites, unlike the skin of whales. An attempt is made with a silicone-like ship color which certain small structures during curing to emulate the biological model. The advantage of this method is that no toxic substances are used.

Research has shown that tiny nanoparticles of vanadium ( V) oxide suppress the growth at interfaces. Vanadium in this case acts as a catalyst, which forms highly toxic compounds for microorganisms.

A new painting based on Nanokompositlacken which have different electrical conductivities and applied in a multilayer system on the hull. Is allowed to pass through these layers in the region of low currents of 0.1 milliamperes ( mA) per square centimeter. At specified time intervals, the streams are then reversed. Due to electrolytic processes thereby the pH of the water in the immediate vicinity, which counteracts an increase of mussels, algae and barnacles changes. With a boat fisheries surveillance in Mecklenburg-Vorpommern is currently (2012 ) tested the effectiveness.

History

Particularly damaging was fouling with wooden ships, as they were used until the 20th century. On the wooden planks encamped on very much. It began in the 18th century, partly in order to cover the vessels with copper plates. This also protected against the shipworm, a wood-eating species of shellfish.

Long forgotten was a technique of the Romans: they covered their ships with lead plates to inhibit fouling. Lead is soft enough to hammer it on woody underground can. This technique has been documented for example in the Nemi ships.

A severe disciplinary sanction in seafaring was careening in which the person suffered by the sharp-edged fouling deposits with severe injuries often fatal opportunistic infections.