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Engineering, United States

Boeck F.,TU Berlin | Hochkirch K.,FutureShip GmbH | Hansen H.,FutureShip GmbH | Norris S.,University of Auckland | And 2 more authors.
4th High Performance Yacht Design Conference 2012, HPYD 2012 | Year: 2012

In contrast to modern sailing yachts, ancient sailing canoes did not use a foil-like shaped keel. This fact raises the question of how the hydrodynamic side force generation of a canoe hull in upwind sailing conditions is achieved. The progression from U- to V-shaped main sections indicates an interesting design development. A windward side force is generated by vortex systems, which develop on the stem and follow the line of the keel. The fluid at the windward hull surface is accelerated and induces a low pressure area which results in a net side force. This phenomenon shows similarities to Delta-Wing aerodynamics. The sailing performance and the lift generation of different slender hull designs is investigated in detail utilising RANSE-CFD (CFX). The deformed free surface surrounding the hull is simulated in order to achieve realistic results in agreement to previous towing tanks tests. Furthermore, the results of numerical simulations and results gained in other projects are used as input data for a Velocity Prediction Program (VPP) in order to simulate the behaviour of Polynesian canoes in different sailing conditions. The performance advantage of V-shaped hulls over U-shaped ones is shown. Scientific evidence for the capability of Polynesian explorers to sail with traditional canoes against the prevailing wind direction, in order to find new land to settle on, has been provided. In future developments of multihull racing yachts, the effects described in this paper should to be taken into consideration. As demonstrated, the development of vortex systems can have a positive influence on side force generation, but thereby negatively affects the drag coefficient. By investigating ancient canoe hulls, phenomena were discovered that may be applied to optimisation processes of modern racing yachts.

Junge T.,University of Auckland | Junge T.,Yacht Research Unit | Junge T.,TU Dresden | Gerhardt F.C.,University of Auckland | And 5 more authors.
Journal of Aircraft | Year: 2010

This paper discusses how to maximize the drive force produced by an upwind sail. It aims to provide a better understanding of the behavior of this force as a function of the heel angle of the yacht and the wind speed. It also discusses the corresponding optimal spanwise loading distributions. An extended lifting line code, based on Weissinger's method, is developed to analyze the performance of an isolated mainsail in upwind conditions. It is extended to account for the heel angle of the yacht via effective angle theory, and an image sail is used to model the influence of the sea surface. Profile drag is modeled using experimental data. The extended lifting line code is validated against wind-tunnel measurements and data from the literature. A second code is then used to optimize the spanwise loading on a mainsail such that the drive force is maximized. Constraints are implemented to ensure positive circulation over the entire span and to limit the sectional loading to realistic values. Finally, the extended lifting line code is inverted to calculate the twist distribution necessary to produce the desired, optimized loading distribution for a given sail planform. The calculated twist distribution is found to be realistic and achievable. Copyright © 2010.

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