Foil technology


Nowadays, it is difficult for a professional of the nautical world to have never heard of foils. But do we know all the details, including the specifics of the materials used, the applications in various fields, the combination with different propulsion methods and the current research on this topic? We asked the expert Luca Rizzotti the state of the art of this technology and how foil design is evolving today


According to Luca Rizzotti – Founder of the Foiling Organization, Founder and President of the Foiling Week and the We Are Foiling Group – today the design of foilers is experiencing a moment of great evolution thanks to greater computing powers.

These have allowed designers to pass from very simplified analytical models up to much more accurate and advanced models obtained using software that fall into different categories such as FEM (Finite Element Method), CFD (Computational Fluid Dynamics), VPP (Velocity Prediction Program), TO (Topology Optimization), to name a few.

The Foiling Week is the first and unique global event dedicated to the foiling boats and to their sailors, designers, and manufacturers. Its 10th anniversary edition took place in Malcesine (Lake Garda) from June 26 th to July 5th (Courtesy Martina Orsini)

Foilers in sports

Foiling has become increasingly popular in the nautical sector, from sports such as the America’s Cup to every sector of boat design and construction.

The solutions adopted on the catamarans of the America’s Cup editions (AC72 class) have given a strong boost to the evolution of the smaller classes: as in the case of the AC75, a completely new configuration proposed jointly by ETNZ and LR in 2019 for the AC 36. The system allows the use of one foil as a lifter and the other as a righting moment. The efficiency of this configuration can be seen in the speeds expressed by even the smallest AC40s that exceed 50 knots.

The foils are designed mainly using software called CFD, or Computational Fluid Dynamics. The purpose is to visualize and simulate the flow of the fluid on the surfaces.

The main materials for the construction of foils are carbon: for example, in the case of the Imocas it is ‘solid’ (in the America’s Cup instead they are made of steel).

Peacock (Courtesy Martina Orsini)

Sails & Engines

Luca thinks that the main differences between the foils used on motor and sailing boats are of two types. “Nowadays, the foils used in the sailing world have mainly a competition purpose, they are therefore designed to obtain maximum speeds even at the expense of stability. They also operate in a particularly complex system where changes in wind intensity and direction lead to important variations in lift and angles of attack”.

When used with motorboats, on the other hand, “speed regulation is a ‘fixed’ element that can be easily followed by foil regulation software. Furthermore, the stability of the foils is typically a more important factor than the maximum speed obtainable so that one of the main reasons for their success is comfort”.

The evolution of foils is continuous and very quick. “Just think of the AC40s, which reached the speed of the first generation AC75s in one year. However, generally speaking, the foils will go on towards greater ease of use, both in terms of design and through mechatronics.”

Overview of tested wing profile and planform shapes; an example of RANS calculation with the vertical strut included (Courtesy Luigi F. Minerva MARIN)
The article continues with...