Past and present of foiling by Richard Mason
You would be forgiven for thinking that foiling sailboats are a recent innovation. Granted, the speed at which the technology has made it into the mainstream in the last few years has been astonishing, and is a testament to the influence that the America’s Cup has over our sport. However, in reality, the hydrofoil, and specifically the hydrofoil sailing boat, has been around for a long time.
The first known sailing hydrofoil was built by Americans Robert Gilruth (who was later the head of NASA’s manned space program) and Bill Carl in 1938. Unimaginatively named ‘Catafoil 1’, the boat lifted onto its foils at 5kts and was said to cruise at around 12kts. Gilruth went on to seek financial assistance from the US Navy to build a second boat, ‘Monitor’. Remarkably, the original plans for Monitor included, not only hydrofoils, but ‘two fixed aluminium sails’ as well as ‘a mechanical computer which sensed the forces on each stay and calculated the desired angle of attack for the rear foil to avoid pitching’. Something that is banned by modern day America’s Cup rules, but is so effective that some of the current America’s Cup teams employ a computer to adjust their AC45 Turbo’s rudders to the perfect pitch during testing.
The Monitor project was forced to abandon the fixed sail due to lack of funds, but in 1956 the boat (with soft sails and automatic rear foil adjustment) reached a recorded speed of 30.4kts: unofficially, she’s said to have reached speeds close to 40kts. Gilruth had wanted to market his hydrofoils to the public, but the concept was ahead of its time, and the stainless steel foils were too expensive to produce, and fatigued too quickly.
Foiling remained on the fringes of the sport, but in no way was the concept forgotten. Over the years, some of the best technological minds in sailing have been enticed into advancing public understanding of foiling sailboats. The maths was undeniable – hydrofoils give significantly less drag at the same speed as a conventional planing hull.
In 2012, the 34th America’s Cup saw the birth of the AC72’s. Oracle introduced a rule that was supposed to prevent the boats from foiling. ‘T foils’ were not allowed on the dagger boards, moving surfaces were not allowed on the main foil and the rudder pitch angle had to be fixed before the start. Team New Zealand, however had other plans, and under the supervision of technical director Nick Holroyd the flying AC72 was airborne.
Roll on one cycle and the flying machines have been embraced. Next year will see an evolution of the previous rule. The boats will be smaller but faster than the AC72’s and crucially they will be able to tack on the foils, marking a massive performance gain. It is important to note at this stage that it is not just foil technology that is pushing the speed of these advanced boats. Wing rigs, composite technology, better aerodynamic understanding, fluid dynamic computer modelling and better systems design also have a very influential role in improving speeds and handling.
As the technology evolves, so does the role of the sailor aboard the boat. Most notably, the physical demands of a 50 foot boat sailing at 50 knots are far higher than ever before.
Before the foiling revolution there were 17 men on the IACC America’s Cup boats. Each had a very specialised role, but most of those sailors were needed for handling the 750m²of cloth that powered these beasts. For the 2017 America’s cup, the boats will probably rid themselves of soft sails all together and opt not to use a jib or a gennaker. With the massive increase in pace and efficiency of the boats, the apparent wind speed and direction stays surprisingly similar over the entire course. Unlike conventional sailboats extra sail is not needed downwind. Whilst foiling upwind, the apparent wind direction is so far forward that a conventional soft jib would just flap like a flag.
By swapping soft sails for moving appendages you reduce the need for bodies on the boat. In fact, the wing trimmer and the helmsman trimming the foils is all that’s needed.
The other four men on the boat are muscle (and occasionally offside helmsman). Of course there have always been grinders onboard, but the requirements of these new foiling boats are a bit different. The requirement of the grinders has changed dramatically. In 2007, the work to rest ratio on the IACC boats were 1:6; in San Francisco on the AC72’s the ratio was 6:1. The sailors have to maintain a much more consistent output. This is because they are now moving hydraulic fluid instead of sheets. The grinders pressurise the fluid in a tank so the energy can be stored and used at any time to move the wing or the foils. Since these are in almost constant motion, the tank can always be topped up.
This is going to be one of the most interesting features of the next America’s cup. As previously mentioned the new boats will be foiling tacking. In reality this is an incredibly energy consuming task. The entire tank will be emptied over the course of the tack. Currently it takes just over three minutes to fill a tank from empty, but the constraints of sailing in Bermuda means that the boats will have to tack approximately every 90 seconds. As the technology exists currently this is impossible to achieve.
Having stronger sailors to turn the handles, decreasing the energy needed for each tack, or improving the efficiency of the hydraulic system among other advances could overcome this problem. If a foiling tack cannot be achieved every time, tactics come into play. Having to decide when to use the foiling tack will be like deciding when to use KERS in Formula 1.
In the fifty-nine years since Monitor, technology in so many different sectors has advanced together to allow these amazing machines to race as we see them now. We are on the cusp of a massive performance gain– the foiling tack- but soon (possibly before next summer), with the small improvements of each piece of the puzzle, tacking on the foils will become normal. I wonder where technology will take sailing next.