LAUSR

Ship hull paint roughness considerably affects ship’s resistance. During the ship design stage, the added resistance coefficient, Δ C F , is used as the parameter of added resistance due to roughness. Δ C F is commonly estimated by the ITTC1978 formula using Ks as the roughness parameter. Ks is measured as the average hull roughness (AHR). AHR is composed of the average of Pt50 values (difference between the maximum peak height and the maximum valley depth in the evaluation length of 50 mm) collected from multiple locations on the ship’s hull. However, it has been indicated that not only the roughness height parameter but also the wavelength parameter can affect frictional resistance. In this study, we try to develop a new method for estimating the added frictional resistance using the rotating cylinder test. The relation between the friction increase rate (FIR) (%) and the roughness Reynolds number ( k + ) is investigated. FIR (%) is dependent not only on the height parameter but also on the wavelength parameter. The projected area of the “cones” above the non-effective thickness, δ s , to stream direction per unit area, A all , which is called the cone projected area (CPA), is calculated using the roughness parameter Rc (i.e., the average height of roughness components) and the wavelength parameter RSm (i.e., the average length of roughness components). The strong positive correlation between the FIR (%) and CPA is confirmed. Using this relationship, the FIR (%) of the roughness cylinder can be easily estimated from Rc , RSm , and δ s .