The development of biofouling on ship hulls is known to be deeply damaging for the overall performance of the vessel. The real effects of soft fouling, especially due to biofilms and diatoms, are however not yet understood and precisely defined. The current work numerically assesses the influence of an increase in surface roughness due to soft biofouling over the hydrodynamic performance of a containership. The simulations are carried out through MARIN’s in-house software ReFRESCO. Unsteady free-surface computations are used to evaluate both the resulting frictional drag, and the wave profile modification for different input surface roughness values. The results show that frictional resistance at 14 knots is increased of up to 45% for a limit equivalent sand-grain roughness height ks = 300 μm, correspondent to biofilms. Residuary resistance at the same speed suffers decreases of maximum 2.5% in the same range. These consist in hull pressure variations in the aft and transom areas of the vessel, and in small height differences in the wave pattern. A dataset obtained from monitoring of the containership for five years is used to study the added frictional resistance evolution due to roughness. Holtrop & Mennen
procedure integrated with environmental variables show a maximum increase of ΔCF = 1.4 · 10−3. The methodology proves useful to identify potential drydocking periods, and to provide an overview
of the added resistance trend. It should however be implemented with Machine Learning models to improve accuracy, in case the precise influence needs to be assessed. A novel comprehensive soft
fouling growth model is created to assess the surface roughness ks and ΔCF time evolution. This constitutes one of the few attempts in the literature to create a model that simultaneously considers the
effect of multiple environmental and operational variables based on the GPS position. Light intensity, sea surface temperature, draft and concentration of nutrients. Increases of up to 100 kN in resistance
and of ΔCF = 0.001 are observed if only diatoms are considered are integrated. Temperature and nutrients result to be more relevant for growth, in comparison to light intensity and draft. A sensitivity
study is also carried out to prove the small dependence on the choice of the analytical approach. A comparison of the growth model + CFD results with data processing show that the analytical procedure
provides a good indication on the growth trend, while added resistance intensity is underestimated in the order of ΔCF = 4.65 · 10−4.