First a disclaimer: This article is written based on facts as I understand them, and only includes the foils that I have personal experience with, or knowledge about.

In the beginning

Once upon a time there were some bored moth sailors in Perth. These gentlemen had some crazy ideas about how to make their boats go quicker. John used Jane’s Surface Skimmers as a guide to come up with the NACA 63-412, as the hydrofoil of choice for his design. After a period of evolution the first generation of competitive moth hydrofoils was born.

The sizes of the foils were obtained through a series of trial and error experiments, with the final size being a foil that was of rectangular planform, 120mm x 850mm with an area of 1,020sq cm. With the art of setting up a moth in it’s infancy these foils were run with a designed angle of attack from 0 to +2 degrees. In reality this was simply not enough in most conditions, and all the boats of the time adopted a noticeable bow up attitude in average conditions as they sought more lift. These foils, in the hands of Rohan Veal changed moth sailing forever winning the World Championships in 2006, just as Steve Shimeld had done 19 years earlier in Gladiator a the Adelaide worlds when he proved once and for all that a Skiff could win in all racing conditions, including the heavy airs that had been the domain of the scow up until that point.

The second step

After the 2006 worlds, John Ilett introduced the first of the second generation Fastacraft foils. The second generation Fastacraft foils followed on the success of the first generation and continued to used the NACA 63-412 section, but now in a semi-elliptical planform. The overall width of the foil increased from 850mm to 980mm, and kept an almost identical with the area only dropping slightly to 1,010sq cm.

Everything else about these foils has largely remained the same as their predecessor, and these foils dominated, winning everything in their path until the Bladerider.

Enter the Bladerider

Using the Fastacraft v2 foils as the starting point, Andrew “Amac” McDougall set out to design foils that were would facilitate an earlier takeoff, and provide better control than the current state of the art foils that John Ilett was producing. At the world championships in Lake Garda, the Bladeriders showed superior control over their competition. A lot of this superior, more responsive control that the Bladerider experienced at the time was being attributed to the Bladerider’s control systems, which were a significant step forward at the time. Whilst the control systems were a large portion of the gain the Bladerider made over the competition, close inspection of a Bladerider foil reveals a number of key changes in the foil section, flap and planform, all of which are working together improve the on-paper performance and control.

Unlike the standard NACA section used by John Ilett, Amac designed his own section specifically for the Bladerider.

As you can see in the above diagram, the Bladerider section is a thicker (14%), more heavily cambered section than the 12% NACA. The thicker aft section, mechanically allows a much stiffer flap to be achieved compared to the NACA section.

The foil planform also has an effect on their characteristics. The graphs below show a comparison of the v1(square), and a simplified v2(tapered) Ilett foils against a theoretical Bladerider foil that used a NACA 63-412 section, and had no bulb at 15 knots (upwind speed) all with no flaps.

This analysis was performed whilst designing my own current foil and shows two interesting things. Firstly, the foil planform differences between the v2 Fastacraft and Bladerider have no significant differences, however the poorer performance of the old, square v1 Fastacraft planform is clearly visible. The v1 foil produces significantly less lift than the higher aspect foils for a given angle of attack and drag profile.

Put another way, to achieve the same lift as a v2 Fastacraft foil running at +1 degrees AOA, a v1 Fastacraft foil would need to run at +3 degrees AOA and as a result it would produce an extra 8 pounds of drag at 15 knots.

The numbers also show that the Bladerider profile has slightly lower drag, however this does not translate to real life as the Bladerider does not use the same section as the other two foils.

Another key change for the Bladerider foil was a design that included a significantly wider, stiffer tapered and generally more aggressive flap than the Fastacraft foils, that was designed to operate in a ~20 degrees range (+- 9.6 degrees). The Bladerider foil is constructed in two separate pieces that are connected using Sikaflex, whilst this method can cause problems if the join fails, it results is a very tight, join between the flap and the foil with a small gap.

Comparing the two

The Ilett v2 and the Bladerider foil each have strengths and weaknesses. The Fastacraft foil has a lower overall drag profile, (which has been confirmed by tank testing conducted by Bill Beaver), however the Bladerider foil has better control characteristics as a result of it’s foil section and flap design.

On the racecourse, the ultimate performance of the two foils are very similar and there are a number of reasons for this. The first reason is that all Ilett v2 foils are not identical. John Ilett continued to add subtle improvements to his foils, increasing the flap size and improving flap stiffness which has improved control. Other areas where the Fastacraft boats have evolved is the enhancement of their control systems. Both boats have now been developed to the point where the individual skill of the sailor is a bigger factor in boat performance than the foil design itself.

The third generation

After leaving Bladerider, Andrew McDougall has once again designed a new set of foils for the Mach2 which continues to evolve his design. The Mach2 foils appear to be squarely aimed at building on the strengths of his previous design work at Bladerider, whilst aiming for an overall lower drag profile.

The flap and bulb from the Bladerider remain and have been refined, however the thicker section that was used for the Bladerider has been replaced with a much thinner, lower drag section.

The Mach2 foils are stiffer, utilising high modulus pre-preg carbon fibre in their construction. The flap hinge combines the best of the Fastacraft and Bladerider foils with the Sikaflex hinge being replaced by a stronger, flexible Kevlar one, as used by Fastacraft since the v1 foils. The foil planform is a higher aspect ration, which will result in a reduction in the drag caused by tip-loss. The section has a greater sweep angle compared to the Bladerider which will further reduce the overall drag of the section. The foils are also designed with a larger angle of attack “out of the box” which allows the boats to adopt a level as opposed to a bow up attitude which has been common throughout the fleet prior to the Mach2.

These foils were used to good effect by Bora Gulari to convincingly win the 2009 moth worlds in Cascade Locks.

John Ilett has also released a third generation foil the two piece foils are bulbed, although the bulb is much smaller than the others. The foils also have the highest aspect ratio or any foils in the fleet, with a tip to tip span of 1,120mm. Although similar in appearance unlike the Mach2, the Fastacraft foil has an aircraft style hinge, seeking the next level of refinement. The performance of this foil is unknown at the time of writing.