Analyses of Foil Configurations of IMOCA Open 60s with Towing Tank Test Results

Abstract

The main aim of this master thesis is to evaluate the hydrodynamic effects of two different foil configurations used on a monohull sailboat. This representative vessel is the IMOCA Open 60 which is the most extreme sailing racing monohull in the world, and skippers sail it in races such as the Vendée Globe. According to class rules, the powerful racing sailboats have to be equipped with five appendages which are typically two rudders, a canting keel, and two daggerboards. Nowadays, the teams in this competition prefer one of two different daggerboard configurations which are straight and curved foils. The primary objective is to compare the straight and curved foil configurations based on effective draft values in some upwind conditions experimentally. For that purpose, the 1/8th scale models of the Open 60 sailboat hull and its appendages were used for getting experimental results in the towing tank facility at Southampton Solent University. Firstly, a test matrix was prepared for the various appendages configurations. The main parameters were measured Side Force, Drag, Heave and Trim in an array of conditions (heel angle, leeway angle and velocityFroude Number) during the towing tank tests. The viscous and wave resistance values were calculated based on ITTC formulations, and then the resistance and side force values were scaled to full size based on 1/8th scale factor for each condition. Also, some towing tank tests were done with only the bare hull for obtaining the form factor values of the upright and heel states. The uncertainty analysis calculations were applied to determine the uncertainty of these experiments based on the ITTC-Recommended Procedures and Guidelines. The available model sizes of the straight foil configuration, keel, bulb, and hull were employed for the towing tank tests. However, the curved daggerboard dimensions were taken from pictures of the new generation Open 60 sailboats. The representative curved foil was designed in 3D, and it was manufactured in a plastic material (PBC) by the 3D printer and then it was covered with carbon fibre. The 0° and 40° canting keel conditions were evaluated based on the effective draft and righting arm and the 40° canting keel was employed together with the 1/2- full straight and 1/2 - full curved daggerboard configurations during the tests. The straight and curved daggerboards were compared at certain sailing conditions according to the effective draft and heave values to find the more effective and lifting foil configurations in the upwind conditions. As a result, the fullstraight foil configuration is the most efficient daggerboard configuration in the upwind conditions however the curved daggerboards have more lifting force advantage due to their shapes as compared with the straight foils despite being less efficient in the upwind conditions