That final millimetre


After 30 years’ developing bespoke CFD tools and applying them to the design of an impressive range of craft from IACC America’s Cup yachts to commercial hydrofoils, yacht designer and ACT Technologies co-founder Akihiro Kanai took particular pleasure in watching the successful results of his handiwork at a smaller scale, first at the Tokyo 2020 Regatta in Enoshima and then in Marseille at Paris 2024


In 1990 my first serious encounter with Computational Fluid Dynamics (CFD) was a free-surface flow simulation around the stern of a high-speed hydrofoil catamaran, which I undertook as a postgraduate student. At that time a typical workstation had


only 100MB of memory and 32-bit CPUs. Even so, and running at what would today be described as a snail’s pace, it was a big step forward to have this new tool to eval- uate the performance of a vessel; even 35 years ago it was clear that, moving forwards, researching and developing CFD codes was going to become essential for designers to be able to design marine craft to the level of optimisation that would soon be


50 SEAHORSE


expected. But not just yet… because back then the reality was that there were very few commercial codes available. Two years later, in 1992, I continued


my CFD research at Stanford University, but CFD remained a rather esoteric and experimental genre. The CFD ‘journey’ as we look at it today had still barely started. That situation would change suddenly


in 1993 when I was called back to Japan for a new America’s Cup project, which would be using CFD to the fullest extent possible from the outset to investigate hull and appendage solutions. As far as I am aware this Japanese Cup


programme was one of the first serious applications of CFD to real-world marine vessel design. Since then, of course, count- less CFD codes have been developed around the world and CFD tools have become an unremarkable component of such work. Here I will review some of my own work and experiences in the CFD field.


ACC America’s Cup monohulls In the 1990s CFD capable of handling free surface calculations began to be used for the development of International America’s Cup Class (IACC) hulls, with such CFD codes also being developed with accelerating


intensity at research institutions and universities around the world. The Nippon Challenge, of which I was a member, was no exception with development conducted at universities being quickly applied to our own design tasks. The CFD we used at that time calcu-


lated sail forces based on given wind speeds and directions through sail models, with the hull’s attitude changed to balance the forces acting on the hull calculated by the free surface analysis around the hull. This CFD model was quite challenging


for its time. During the project hull designs and simulated tank-testing were repeatedly evaluated using CFD, which as far as possible was then physically validated in the actual tank to test for accuracy. Ten years later, in 2003, this same basic CFD code was still being used in updated form by the GBR Challenge in New Zealand. In parallel with our new CFD tools,


dedicated software was developed to auto- matically generate candidate ACC hull shapes which were then evaluated in the CFD tool. To the best of my knowledge this early combination of CFD and design software allowed us to progress design development much faster than had been seen in previous Cup programmes.


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