The X Sail Racing Team’s boats AUDI e-tron and AUDI Ultra scored a double victory at the X-35 World championships in Denmark: e-tron won Gold, and Ultra Silver. A sizable R&D work preceded the design of the World Champion sails.
The computer was used to design and simulate 24 different configurations. The main focus was on the jib shape, sail trim and in particular the effects of in-hauling the jib – the mainsail design had been updated late in the summer 2014. The influence of the jib entry on the width of the “groove” was explored, as well as the effect of waves in the sail air dynamics in general.
The simulation predicts the driving and heeling forces of the sails. The forces alone are not enough to rank the different sail designs: Even if the drive is better, if the heeling moment increases too much the end result can be worse for the performance as a whole. For an absolute comparison, you would need to use a VPP. To make things less complicated, we formulated an excel sheet to compare the results. A penalty function is applied to the heeling moment, influencing the effective driving force available to power the boat.
An accurate model of the X-35 was created for the simulation, with sails, mast and the crew sitting on the rail. In the model, the sails’ shape can be adjusted numerically so that any change is automatically reflected in their 3D-geometry. A model like this is called parametric. Even the tell tails were included, live, so that they would behave just as in the real boat.
The role of the sailors was significant in the development. We held meetings before the start of the project and during its progress, to assess the results of the simulations together with the sail trimmer and helmsmen, listened to their suggestions and tried to answer questions they had. R & D is at its best, when done in co-operation with the client!
Below: The x-35 model and a part of the 21 different jib shapes that were analyzed.
For the Olympic classes, our R&D work in on going year in year out. This work certainly benefits other classes, too. For instance, when our Snipe designs where updated lately based on what we had learnt in the 470, there was a clear performance jump that also showed itself in the race results. Every simulations teaches us something new about the behaviour of sails and sailboats, and we try to forward the knowledge to all our customers. Next in line are the Dragon sails – their design dates back to 1999.
Below: Flow around the X-35 sails in waves, and other simulation videos.
