Hidden world
For too many years the subject of yacht aerodynamics has been exactly that… JB Braun and Pete Melvin demonstrate how times they are changin’
In this two-part article about modern yacht aerodynamics (yes aero, not hydro), we take a look into the world of a small group of leading-edge thinkers and practitioners who are working away behind the scenes to drive both the sport and the state of the art forward.
Anyone paying attention to the leading edge of the sport will be aware that yacht designers have been devoting more time to aero- dynamics of late. It has been in evidence in the TP52 and Maxi 72 fleets the past few years, but the first place it was really obvious to everyone was on the Oracle boat for AC34 in San Francisco in 2013. That platform had very clearly been designed with a lot of thought towards how it ‘flew’ through the air as well as the water. Despite the attention to detail, even at this level, the sail aero- dynamic and boat aerodynamic aspects of these campaigns have mostly been dealt with independently, with results combined for analysis only afterwards. Here we are going to talk about a team of people, all veterans of AC34 (and many other Cups), who came together to push the state of aero integration forward. How different would boat designs be if you could look at the wind over the hull, sails, crew and equipment altogether in the same model, and really see the interrelated effects of all the constituent parts of the boat on each other? What if you could run that full model through a VPP and see the result of any change, anywhere on the boat, in elapsed time around the course? This is a question that Michael Richelsen of North Sails Consulting and I asked, for a project with Pete Melvin and his design team at Morrelli & Melvin. In the new flying era for boats it was time to seriously start unravelling the aerodynamic mystery.
This article, at its heart, is a look at how modern software and
computational tools are laying the foundation to better understand aerodynamic effects on sailboat design overall. We look at some
40 SEAHORSE
of the tools put into action for one of the latest designs from the board of the Morrelli & Melvin design office, a project referred to as the Superfoiler.
Pete Melvin: ‘With a new concept such as the Superfoiler, there is little existing empirical knowledge to guide development. Conventional design tools allow incremental gains to be made to existing geometry concepts such as monohulls, catamarans or trimarans. Conventional design tools are also typically based on accumulated sailing data, coupled with engineering formulas developed to simulate observed behaviour. But the maths behind these tools is a simplification of the complex physics that takes place in the real world.
‘However, more advanced design tools are steadily becoming available to yacht designers, providing much deeper insight into the complex system of forces and moments operating on a sailing yacht. Improved knowledge and the ability to model unconven- tional geometries now allow the development of much more advanced and higher-performance yachts.’
It was not all that long ago when a sailplan drawing from a yacht designer had nothing below the rig but the 2D shape of the shearline drawn in, as he tried to imagine how fast a yacht might look. Most of the design and analysis was performed on the shape of the hull plus some basic investigations into the appendages. As design tools evolved from artists’ paintbrushes to more scientific/mathematical methods, reinforced by a century of research, designers started to turn their gaze up from just the hull shape and appendage surfaces, towards the free surface of the water and how the appendages and hull affected that free surface and ultimately influenced the drag produced.
Drag of course, in all its forms, has a significant effect on how the yacht will perform. Those days when yacht designers looked
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