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.

Keywords:

• High-speed craft (HSC)
• planing hull
• planing surfaces
• vee hullform
• monohedric hull
• monohedral hull
• Savitsky long form
• hydrodnamic resistance
• conformal mapping

Additional information

Notes on contributors

C Bertorello

Professor Carlo Bertorello is a Naval Architect, taking his PhD in 1998. He has conducted research at the University of Naples Federico II since 1999 in the area of Naval Architecture. He was appointed Professor of Small Craft Design in 2000. He has also been contract Professor of Naval Architecture and Marine Construction for the Master’s Course in Yacht Design at Milan University since 2001. Carlo was a member of the Italian Delegation at IMO SLF Sessions held in 2000 and 2003, and the Organizing Committee of the International Conferences FAST 2003, ICMRT 2005, ICHD 2006. He is the author of more than 35 scientific papers on the topics of high-speed craft hull forms, multi-hull ship stability, multi-attribute design procedures and composite materials.

L Oliviero

Dr Luciano Oliviero is an aerospace engineer and naval architect. He has held positions as performance engineer at FIAT Safety Center and structural designer at Magnaghi Aerospace. He was a PhD student at Naples University, being involved in the research program concerning high-speed and planing craft.