55 Sustainable Maritime Transportation and Exploitation of Sea Resources – Rizzuto & Guedes Soares (eds) © 2012 Taylor & Francis Group, London, ISBN 978-0-415-62081-9 Endplate effect propellers: A numerical overview Stefano Gaggero & Stefano Brizzolara Department of Naval Architecture, Marine Engineering and Electrical Engineering (DINAEL), Genoa University, Genoa, Italy ABSTRACT: Energy saving is a primary objective, historically the first and, probably still now, the most important one, in the design of marine propellers. Modern design approaches, like fully numerical lifting line/lifting surface codes and optimization applied to potential panel methods satisfy this objective and allow to design conventional propellers with maximum efficiency for a given operating point. On the other hand nonconventional propellers, like CLT and Kappel like geometries, represent a further opportunity to increase efficiency and reduce the risk of cavitation. In the present work a numerical analysis of uncon- ventional propellers will be carried out. Two different numerical approaches, a potential panel method and a RANS solver will be employed. The analysis will highlights the peculiarities of these kind of propellers, the possibility to increase efficiency and reduce cavitation risk, in order to exploit the design approaches already well proven for conventional propellers also in the case of these unconventional geometries. main advantages of CLT propellers, higher values of efficiency (thus lower fuel consumption, air pol- luting lower emissions), higher value of thrust per unit area (thus higher ship speed and lower opti- mum diameter), lower noise and vibration levels with better margin for face cavitation and cavita- tion inception speed. The gain in efficiency is obtained by the dis- placement of the maximum load towards the tip, that is made possible, without high noise and energy losses (typical of tip loaded conventional propellers) by the presence of the endplate. In fact the outer radial sections of the blade contribute more efficiently to the generation of thrust: veloci- ties are higher and, geometrically, local pitch angle is lower, i.e., the local lift is more “aligned” with the axial propeller direction. A way to achieve high efficiency is, thus, to produce the most part of the required propeller thrust in this region of the blade. The additional span (but not in the radial direc- tion!) provided by the endplate lets to locate the maximum load near the blade tip with a gradual and smooth reduction of the loading curve. In this way it is possible to avoid the presence of a strong tip vortex and higher values of induced velocities on the propeller plane, whose effect on the hydro- dynamic pitch is fundamental in achieving high values of efficiency. The presence of the endplate itself, that increases the pressure difference on the tip region, and lets to adopt a finite chord at tip, produces higher value of thrust per unit area and a local unload of the sections. The resulting smaller optimum diameter lets the propeller to operate in a more uniform 1 INTRODUCTION Energy saving is a primary objective in the design of marine propellers. The constant increase of oil price, the more strict regulations in terms of air pollution and the limits for NO X and SO X emissions require more and more efficient designs. At the same time, also requirements in term of radiated noise and vibration emissions became more strict: avoid negative effects on marine life and reduce the risk of hydro-acoustic signature are the primary aims of new commercial and navy constructions. Unconventional propellers, like Contracted and Loaded Tip (CLT) propellers, represent a valid answer to all these demands that can be fulfilled without the employment of completely different propulsive solutions, like contra- and co-rotating propellers or by the adoption of ducts, stators or wake regularizers. The first concept of tip loaded propellers goes back to late seventies: Tip Vortex Free propellers were the first application of the Loaded Tip con- cept, that quickly evolved toward the CLT solution when also contraction of the fluid vein has been taken into account for the definition of the optimal geometry (www.sistemar.com). CLT propellers are characterized by a monot- onic increase of pitch from blade root to tip, a finite chord at tip, moderate values of skew and an endplate at the outermost radial edge of the blade towards the pressure side. Full scale installa- tions and observations, together with model scale measures and theoretical studies, as reported by SISTEMAR (wws.sistemar.com) identified, as the