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The Aerodynamics of Sail

I have recently discovered an interesting series of technical articles put forward by WB-Sails of Finland and as many of these are related to the setting of sails for small sailboats, I thought you'd like to know about them. There are also test results from two Finnish wind-tunnels that serve to further back-up the technical explanations offered.

sail aerodynamics

You will also find some interesting inter-active simulation programs that will accept your own data—such as for sail settings, heeling force, etc.

No doubt, like most studies dealing with subjects that are constantly evolving, some of the claims and conclusions will still be debated at length at your local yacht club bar, but here is a good place to start. Below is the link, and from there you will find a more detailed index…enjoy!

Now if this seems too complex or is more than you need, you might enjoy the more simple explanation offered here for starters:

But if you'd like to read and study more, here are two fine books that delve deeply into the subject of aerodynamics as related to sailing:

First, the long time classic by the noted Polish engineer, sailor, author and professor, Czesław Antony Marchaj, with his book (last updated in 1988), entitled Aero-Hydrodynamics of Sailing that also covers much of his wind-tunnel work at the University of Southampton, UK—noted for its specialty in Naval Architecture.

sail aerodynamics book

And then, more recently, a 2009 book by Fabio Fossati entitled:
Aero-Hydrodynamics and the Performance of Sailing Yachts: The Science Behind Sailboats and Their Design

If you've not heard of Dr Fossati, then you probably soon will, as this is considered an important publication for those with the technical knowledge to follow it.

Here is a brief bio: Fabio Fossati was born in Milan, Italy in 1962, and graduated in Mechanical Engineering at Politecnico di Milano, receiving a Doctorate in Applied Mechanics in 1994. Now Professor of Aerodynamics of Sail, Elements of Fluid Mechanics, Elements of Naval Architecture and Mechanical boat sailing courses leading to a Master's Degree in Design at the Nautical Politecnico di Milano and University of Genoa. Since 2004 he has been the scientific coordinator of research, and was responsible for the activities of the Wind Tunnel of Politecnico di Milano as Technical support for the PRADA Challenge and the 2003 America's Cup team Luna Rossa Challenge for the 2007 America's Cup.

One has to be warned however, that the above book is a very technical one, for a potentially very complex subject.

If you'd prefer something more accessible, then The Symmetry of Sailing by Ross Garrett should be a more satisfying choice. Brief bio: After a few years in the US, Ross Garrett returned to New Zealand to research nuclear physics, combining this with racing small catamarans and trailer sailers. The Symmetry of Sailing is based on a series of lectures given at the University of Auckland.

Of course, the move to 'Wing Sails' for the 2013 America's Cup boats brought in a new science and significantly raised sailing performance level, but there are many practical reasons why these rigid rigs will not serve for most sail boats. However, it would not be surprising to see larger wing masts that still carry soft sails, specified more for certain performance-oriented craft.  Even my W17R goes that way, with a CF wing mast of just under 3 to 1 chord to width.  More on this now available on this website.

Added 2021:   And that prediction of rotating wingmasts carrying highly efficient soft sails came true with the remarkable foiling Americas Cup boats of 2021.    These boats have demonstrated that if the soft sails are twin ply and fitted with internal batten controls, they can be at least as efficient as were the rigid wingsails, and because of their high degree of adjustability, are probably even more efficient.   An exciting prospect moving forward.

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