Benoit Marie at frontend of Mini-Transat after Yacht Research project

by David le Pelly on 28 Nov 2013
Benoit Marie, currently lying a close second in the Mini Transat, studied for six months at the Yacht Research Unit at the University of Auckland.

Whilst at the Yacht Research Unit he built a 1/5 scale model of his Mini using flax-fibre composites which he then tested in the Twisted Flow Wind Tunnel. As well as generally optimising his sail plan, he looked in particular at the use of double-surface sails and their ability to perform more efficiently than conventional thin sails.

The prototype Mini 6.50s are at the cutting edge of design. The rule is as close to a true box rule as any come (just a few necessary stability requirements). Keels that cant and translate, rigs that cant to windward, water ballast and a huge sail area to displacement ratio, result in the most technically advanced boats around.

The next major refinement will most likely come from the sails. The power produced by a reaching sail is basically dependent on the luff length. The Mini 6.50 suffers from a relatively short gennaker luff length compared to its chord because of the mast height limit. Increasing the efficiency around the luff will make the boat go faster.

By adding a double-surface (e.g. inflatable aerofoil) to the leading edge it's possible to significantly increase the efficiency and the amount of lift produced by the section. Just as inflatable battens are now commonplace in many headsails, the technology to hold a luff pocket inflated to the desired shape is available.

The wind tunnel results showed the double-surface gennaker to be more efficient than a conventional thin sail. Certainly there's some work to do in sorting the logistics, and how to inflate the sail once it's up, but the gains could easily be huge.

Why don't we see this used more often? Because the vast majority of racing rules prohibit it.

It's from development classes such as this that technology improvements will eventually trickle down into general racing and cruising.

In the images the double-surface luff of the gennaker can be seen. The Yacht Research Unit are not aware if Benoit carried this particular research project into the actual race - with handling the double surface luff still being an issue.

At latest report Benoit Marie was just 14nm behind the race leader with 970nm to the finish. The two had a big break on the rest of the fleet and were sailing faster - so the rich look set to get richer.

The Twisted Flow Wind tunnel is one of several specialist facilities at University of Auckland's School of Engineering, Yacht Research Unit

The Faculty of Engineering also has a range of state-of-the-art facilities, including:
• A Yacht Research Unit which has been involved in the design and testing of boats competing in the America’s Cup, Volvo Ocean Race, and many other regattas since its inception in 1987.
• Twisted Flow Wind Tunnel.
• Boundary Layer Wind Tunnel.
• Centre for Advanced Composite Materials.
• Light Metals Research Centre.

Graduates of the Auckland University School of Engineering include Olympic Gold medalist Russell Coutts, Olympic Bronze Medalist John Cutler, and 2012 Olympic Gold Medalist Jo Aleh and many more top international sailors.

David le Pelly is also a member of Emirates Team NZ's design team for the 34th America's Cup specialising in Aero and Instrumentation.

For more on the Yacht Research Unit click here