A systematic study on the influence of scale, hull roughness, and draft on form factor estimation

In recent years, considerable attention has been given to the prediction of form factor of ships and the associated scale effects, as the accuracy of such estimations has come under scrutiny. This paper explores the discrepancies between model-scale and full-scale form factor predictions derived from CFD simulations using a newly developed approach known as the 2- k method. This method enhances the precision of form factor evaluation, particularly when applied at full scale, showing notable improvements for hulls with wetted transoms. This study tests the hypothesis of 2-k and transom correction methods with different numerical tools and methods. It reveals a strong dependence of the form factor on grid resolution across different scales, while aligning well with findings reported in the literature. Additionally, a sensitivity analysis based on uniformly distributed surface roughness is performed. The 2- k method is also applied to systematically varied transom submergence conditions, demonstrating consistent form factor trends across both model and full scales. Furthermore, when evaluating draft variations, the method yields results that more closely match experimental data. These findings suggest that the 2- k method is a reliable tool for estimating the form factor in scenarios involving complex turbulent flow, such as in the wake of the transom. • CFD-based form factor assessment in model and full-scale for five benchmark hulls and two commercial hulls. • CFD-based form factor using two RANS approaches: double body and free surface. • Verification and Validation (V&V) analyses on hull resistance components and form factor for benchmark hulls. • Consistency of form factor results through draft variation with transom submergence in both model and full-scale. • 2-k method estimation provides reliable predictions of form factors for the analyzed hulls.