Mainsail Planform Optimization for IRC 52 ... - Quantum Sails

1 Mainsail Planform Optimization for IRC 52 Using Fluid Structure Interaction Dr. Robert Ranzenbach, Project Manager, USA Dave Armitage, Quantum Sail Design Group (QSDG), USA Adolfo Carrau, Botin Partners, Spain ABSTRACT Most IRC 52 based upon existing TP52 retain their original rig proportions and Mainsail girths to avoid the cost and disruption of a rig change and to not disturb the finely tuned yaw balance. It is not obvious whether the Mainsail proportions essentially dictated by the TP52 box rule (aggressively square topped mainsails) are actually optimal under IRC even though IRC 52 with TP52 style mainsails tend to successfully compete under IRC.

2 To determine the answer to this question, a Mainsail Planform investigation was performed as collaboration between Botin Partners and Quantum Sail Design Group. The Mainsail Planform investigation utilized a Fluid Structure Interaction (FSI) program developed by Quantum Sail Design Group (QSDG) known as IQ Technology (IQT) that consists of sail geometry definition, inviscid Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA), Velocity Prediction Program (VPP), and shape validation (based upon VSPARS) modules. Applicability of the inviscid CFD was validated by comparison to a limited number of viscous flow solutions, RANS analysis, performed by Porto Ricerca.

3 Two mainsails were considered, a conventional TP52 style and an alternative that was chosen to be closer to the IRC default girth values. To maintain sail area and yaw balance, the alternative Mainsail had a longer P and E. The focus of the study was exclusively on upwind performance, to maximize upwind Velocity Made Good (VMG). Results from the study suggest that a TP52 style Mainsail is not optimal under IRC. The combination of rating reduction and predicted performance advantages over a wide range of wind speeds suggest that an alternative Mainsail with larger P and E with girth values closer to the IRC default values is a superior choice for an IRC 52.

4 NOTATION P Mainsail Hoist E Mainsail Foot Length MHB Mainsail Top Width MSA Mainsail Area MGM Mainsail Girth Middle (half) MGL Mainsail Girth Lower (quarter) MGU Mainsail Girth Upper (three quarter) MGT Mainsail Girth Top (seven eights) MHW Mainsail Half Width MTW Mainsail Three Quarter Width MUW Mainsail Upper Width INTRODUCTION While numerous IRC 52 have been optimized to sail under the IRC handicapping formula after competing under the TP52 Rule, few if any, have started the Optimization process prior to their initial launch. In the winter of 2011 however an opportunity to perform a comprehensive Optimization effort in the early design stages was provided with the only initial constraint being the use of an existing female mould from which a pair of TP52 had already been produced.

5 This would ultimately prove an excellent starting point as one of these original TP52, Quantum RACING, would later go on to win the 2011 Audi Med Cup Series. Among the various lines of the Optimization effort, the design team from Botin Partners proposed a study to identify an alternative Mainsail Planform that might offer upwind performance advantages under the IRC rule and that investigation is the focus of this paper. PROBLEM STATEMENT Most IRC 52 based upon existing TP52 retain their original rig proportions and Mainsail girths to avoid the cost and disruption of a rig change and to not disturb the finely tuned yaw balance.

6 It is not obvious whether the Mainsail proportions essentially dictated by the TP52 box rule (aggressively square topped mainsails) are actually optimal under IRC even though IRC 52 with TP52 style mainsails tend to successfully compete under IRC. To determine the answer to this question, a Mainsail Planform investigation was performed as collaboration between Botin Partners and Quantum Sail Design Group (QSDG). The focus of the study was exclusively on upwind performance, to maximize upwind Velocity Made Good (VMG).

7 THE 21st CHESAPEAKE SAILING YACHT SYMPOSIUM ANNAPOLIS, MARYLAND, MARCH 2013 Originally presented at the 21st CSYS, Annapolis, March 2013. Reprinted with the permission of the Society of Naval Architects and Marine Engineers (SNAME). Material originally appearing in SNAME publications cannot be reprinted without written permission from the Society, 601 Pavonia Ave., Jersey City, NJ 07306 BACKGROUND Like many of the parameters controlling a TP52, mainsails are defined within the TP52 rule by a box. As an example, consider the Mainsail requirements set by the 2011 TP52 Rule (Weiland, 2011): Mainsail Hoist (P) shall be no greater than M Mainsail Foot Length (E) shall be no less than M Mainsail Top Width (MHB) shall be no less than M (Authors note- essentially requiring TP52 to have square topped mainsails) Measured perpendicular to the luff at M below the head point there shall be a maximum width (girth) of M.

8 Mainsail Area (MSA) shall be no less than M^2 where MSA is defined by the following equation and MGL, MGM, MGU, and MGT are the Lower (quarter), Middle (half), Upper (three quarter), and Top (seven eights) girths respectively. Mainsail area to be calculated according to the following formula: MSA=P/4*(E+MGL)/2) + (P/4*(MGL+MGM)/2) + P/4*(MGM+MGU)/2) + (P/8*(MGU+MGT)/2) + (P/8*(MGT+ )/2) Alternatively, IRC establishes a default Mainsail girth distribution as a function of Mainsail foot length (E) (Seahorse Rating Ltd.

9 , 2010). The measurement points are defined as the half width of the Mainsail (MHW), the three quarter width of the Mainsail (MTW), and upper width of the Mainsail (MUW). Unless declared as greater, MUW, MTW, and MHW are assumed to be *E, *E and *E respectively. Increases from the default girth values result in a rating assessment. Because the IRC rule is secret , the exact consequences of deviating from the default values can only be known by running IRC trial certificates (the number of which that can be run over a given time period are strictly limited).

10 GENERAL SOLUTION APPROACH The Mainsail Planform investigation utilized a Fluid Structure Interaction (FSI) program developed by QSDG known as IQT (described in more detail in the next section) coupled with the Botin Partners Velocity Prediction Program (VPP) with additional input from IRC trial certificates. Two mainsails were considered, a conventional TP52 style and an alternative that was chosen to be closer to the IRC default girth values. To maintain sail area and yaw balance, the alternative Mainsail had a longer P and E. The focus of the study was exclusively on upwind performance, to maximize VMG.