Biofouling growth study in offshore mooring ropes

Marine biofouling is one of the most crucial challenges in offshore engineering. This study presents an experimental investigation into the growth of marine organisms on synthetic mooring rope segments made from high-tenacity polyester yarn (polyethylene terephthalate - PET), designed and manufactured according to ISO 18692. The rope specimens were continuously submerged for 12 months (from December 8, 2021, to December 8, 2022) at the offshore proving ground of the Admiral Paulo Moreira Institute for Sea Studies (IEAPM), located at Cabo Frio Island, Brazil. The site offers highly favorable environmental conditions for biological colonization, including shallow, calm, nutrient-rich waters influenced by coastal upwelling. The results revealed a typical ecological succession pattern, with species' composition stabilizing around the sixth month and surface coverage reaching equilibrium by the ninth month. Colonization was dominated by soft-fouling organisms, with no continuous fouling layer found in the inner regions of the ropes. However, a few errant polychaetas and isolated bivalves were observed using the internal structure as shelter, indicating localized permeability through the outer braided jacket. Importantly, no structural degradation or significant fouling-related damage was observed. Compared to conventional steel catenary systems, the synthetic ropes showed higher resistance to marine biofouling, alongside the intrinsic advantage of be resistant to electrochemical corrosion. These findings provide valuable insight into the biofouling performance of synthetic mooring ropes in tropical marine environments and offer a foundation for future offshore durability assessments.