Hydrodynamic resistance assessment of non-monohedral planing hull forms based on Savitsky’s methodology

Abstract Planing hard chine hull forms are widely used for high-speed small craft. While monohedral1 deep V forms have been commonly used for more than 25 years, recent trends are toward non-monohedral forms in which most of the hydrodynamic lift is produced by low deadrise areas in the after part of the hull. The deadrise gradually increases in the centre and forebody, allowing greater angles of incidence that are beneficial to reduce wave impact forces and ship motions. Wetted surface also is reduced in comparison to the standard monohedral form, resulting in smaller frictional resistance. This trend has been initiated by the search for better seakeeping performances, and made possible by a general reduction in ship weight due to higher main engine power/weight ratio and lower structural weight. Resistance predictions based on Savitsky’s method are commonly used, although this procedure has been developed on the hypothesis of monohedral geometry for the wetted part of the hull. The results are consequently affected by errors due to wrong assessment of both hydrodynamic lift and centre of pressure In this paper, two procedures for the application of Savitsky’s method to non-monohedral hulls are proposed. The results relative to a recently developed non-monohedral hull form are compared to those obtained by the standard Savitsky method and by towing tank tests. Furthermore, a study for the analysis of error propagation in Savitsky’s long form procedure is proposed.