Combined CFD-EFD methods applied to determining the form factor of vessels with very low length to beam ratio

Abstract

This study investigates the influence of scale effects on form factor determination for a fishing vessel with a low length-to-beam (L/B) ratio, using a combined Experimental Fluid Dynamics (EFD) and Computational Fluid Dynamics (CFD) approach. The research compares the behavior of the form factor between a fishing vessel and the well-known KCS benchmark hull. Results show that scale effects have a more significant impact on the fishing vessel, particularly due to increased viscous pressure losses in the stern region. While the non-dimensional frictional resistance component remains similar between both hulls, the non-dimensional pressure component differ significantly, highlighting the influence of hull shape on pressure recovery. The comparison with empirical methods reveals that traditional marine formulations may not adequately capture full scale form factor of hulls with very low length to beam ratio. Instead, the form factor obtained using aircraft drag estimation approaches shows better agreement with CFD predictions at full scale. Based on these findings, the adoption of distinct form factor values at model and full scale is recommended for vessels with similar geometric characteristics, in contrast to conventional extrapolation practices that assume a constant form factor. This methodology may improve the accuracy of effective power predictions and support more reliable design evaluations.