Dagger-board evaluation for an IMOCA 60 yacht

• Tuning was performed on the canting keel, dagger-boards and rudders of an IMOCA 60 Class yacht.
• Curved dagger-boards were compared with straight boards with positive lift inducing dihedral angles.
• Initial investigations were performed using computational fluid dynamics (CFD) at upwind speeds.
• The yacht׳s trim was modelled in tank tests to ensure correct load sharing between the appendages.
• Both types of dagger-board produced similar performance at windward and reaching speeds.

The IMOCA 60 Class has a complicated set of appendages: with canted and tilted keels, cambered dagger-boards that can be designed to be fitted to the hull in different orientations along with toed-in and twin rudders that can also be configured in different orientations. Curved dagger-boards and straight boards with positive lift inducing dihedral angles have been used in a number of recent IMOCA 60 designs and in other classes, principally multi-hulls. These were considered an option by the client for their new Open 60 design and so a research and development programme was instigated by Owen Clarke Design to compare new curved designs with conventional straight dagger-boards optimised for upwind conditions. It was felt that the modelling of the trim of the yacht was very important to the calculation and sharing of loads between all of the appendages, and so our group chose to use a combination of one third scale high speed towing tanks tests and computational fluid dynamics (CFD), rather than CFD alone to investigate the relative performance between these dagger-board types.