If you’ve seen the SailGP fleet racing, you can’t miss the iconic wingsails – inspired by NASA – which help the foiling catamarans reach such jaw-dropping speeds as they race in iconic venues around the world.
The towering 3D structures are more like airplane wings than traditional sails, and, arguably, the most complex element of SailGP’s high-tech and high-performance F50 foiling catamarans.
Constructed mainly from carbon and titanium with an outer skin of Mylar, the precise shape of an F50 wingsail can be accurately controlled by way of a series of hydraulic rams that independently articulate its individual sections.
Control of the wing is managed by the wing trimmer – a member of the F50 crew who is solely responsible for dynamically coaxing the wingsail into the correct shape for both the wind conditions and angle to the wind the boat is sailing.
Onboard Denmark SailGP Team presented by ROCKWOOL, the athlete entrusted with handling the immense power generated by the wingsail is Tom Johnson – a two-time round-the-world ocean racer, who has also made a name for himself racing in the America’s Cup, before joining up with SailGP.
Tom Johnson - Denmark SailGP Team's wing trimmer
“The coolest thing about the F50 wingsail, is the crazy amount of power at your fingertips – all in the touch of a button,” he explains.
“It’s kind of like flying an airplane with a single button press – I probably have enough power at my fingertips to launch a 737.”
He continues: “But it’s not just about power, it’s also about control, and once you’ve got your head around it, you can really manipulate this wing with the camber and twist controls.”
The high-level engineering behind the F50’s wingsails
To enable racing to take place across the widest possible wind range, SailGP F50 wingsails come in three size configurations.
The ‘smallest’ is an 18-metre (m) / 59-foot (ft) tall version which is used in strong winds above 20 knots (kn) / 37 kilometres per hour (km/h). The largest is a 29-m / 95-ft tall version used when the winds are below 10 kn / 19 km/h. Standing between those two is a mid-range 24-m / 79-ft all-purpose (AP) configuration which can be used in winds ranging from four to 24 kn to 44 km/h.
The 24-metre sail was used in SailGP Season 1, and was fine for racing in lighter winds, but became a risky proposition in heavier conditions due to its size. As a result, the 18-metre configuration was introduced for Season 2.
It is worth noting the use of the word ‘configuration’ here. Rather than there being three individual wingsails – small, medium, and large – the wingsails are built to a modular design, with each size created by slotting together upper, middle, and lower wingsail sections.
Opting for the 18m wing in high winds means less surface area and less drag; so although the profile is smaller than the 24m wing, you don’t need as much wind to power the F50.
Directly joining the top and bottom sections creates the 18-m wing. Two different height midsections can be deployed, either creating the 24-m or 29-m rig. Because the top and bottom sections are always used, the main standing rigging components attach to them – with the shroud lengths adjusted accordingly.
“There is not too much difference in the operation of the different sized wingsails, but it’s more about heeling moment – the smaller wing is more crude, and the power feels direct, whereas the bigger wing is a bit more sensitive and easier to manipulate the heeling moment,” continued Johnson.
SailGP crew preparing the Denmark SailGP Team's 24m wingsail ahead of the race in Saint-Tropez in Season 4
The choice of which size wingsail the fleet will race with on any given day is made by the SailGP organisation based on the expected weather conditions for racing. It is not a decision that is made lightly, as swapping nine rigs from one configuration to another is a time consuming task that can mean the SailGP Tech Team working through the night.
To throw a bigger wingsail on the boat is a bit like an F1 team putting on a brand-new tyre compound – it changes the set up and balance of the boat.
Although it may seem counterintuitive, using a larger wingsail does not necessarily mean greater boat speed, and the highest speeds in SailGP are often achieved using the smallest of the three wing configurations.
This is because having too large a wing up in strong winds can mean the boat gets overpowered and difficult for the crew to control. Additionally, a smaller wing size creates less air drag as it moves through the air, ultimately resulting in faster overall speeds.
The flexibility to reconfigure the wings to match the weather conditions is made possible because the internal systems that control them are based on an array of electronically-controlled, oil-driven, hydraulic rams.
That does away with the complex rope and pulley network used on the America’s Cup AC50 catamarans – the precursors to SailGP’s F50s – and means the process of separating two sections is as simple as unbolting them and unplugging the electronics and hydraulic lines.
The hydraulics in the F50 wingsails include three carbon fibre accumulators – two at the base and one at the top – that maintain an even oil pressure over a vertical span of up to 29m. Each hydraulic line has its own manifold and control system.
In plan form the wingsail’s leading edge is formed by a D-section carbon spar that can be rotated to match the angle of the wind. Attached to the back face of the spar are two tapering structures – a fixed forward section and an aft ‘flap’ – that are hinged together to form the wingsail’s centre and trailing edge.
Members of the SailGP Team technical team working with the electronics of the main wing of an F50 catamaran
Camber and Twist
There are two principal watchwords amongst the wingsail trimming community – ‘Camber’ and ‘Twist’. Both are key elements in keeping the boat under control and sailing at maximum speed for any given set of wind and wave conditions.
Camber is the depth of the curve of the sail when viewed from above. In basic terms, camber regulates the power generated by the wingsail. Inducing more camber (depth) increases power, while less camber flattens the sail and reduces power.
Adjusting the wingsail’s twist – by varying the angle of attack of its trailing edge from bottom to top – also enables the wing trimmer to control the power it generates. Twisting the upper section to leeward (away from the wind) acts as an exhaust for the breeze moving over the sail and reduces the power generated.
The ability to induce both camber and twist is made possible by a set of powerful hydraulic rams positioned at five heights along the hinged centre of the wingsail. Down below, these are operated by the wing trimmer using a set of buttons on the side wall of his cockpit.
The wing trimmer's cockpit
The wing trimmer controls the wing’s angle to the wind using a ‘traditional’ mainsheet (rope) and winch setup. The rotation of the winch drum is driven by the physical efforts of the crew’s two dedicated ‘grinders’ working in tandem on the handles of an upright pedestal winch.
“When you’re starting, you’re trying to keep a certain amount of heel to keep the windward hull out of the water, but as you transition into take-off, you want the boat to be more flat, and then into a windward heel,” Johnson explains.
“It’s all about synchronisation with the Flight Controller, so that you roll the boat to windward as you take off.”
Breaking the speed barrier
As the SailGP fleet looks to break the 100-kilometre per hour barrier, experts are analysing which elements of the F50 could be evolved to achieve more speed – but Johnson reveals that the current configuration is close to perfect, right now.
“The big evolution came just before Season 3 – now we have the modular wing settings, so we can decide a few hours before racing which is the most appropriate set up for racing in the day’s conditions.”
He adds: “You can almost always improve small details, but for a one-design series, the F50 wingsail is at a super high level. We can manipulate them a lot, so we’re looking more at the platform and the foils as opportunities to increase top speed. As we improve those elements, we’ll open up more evolutions of the wingsail, and we’re still learning a lot about the full potential of that every day.”
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Sailing vocabulary
- Foils - Foils are 'ski-like structures' mounted below the hull of the catamaran. When moved through the water, they generate lift helping the F50 to fly.
- Drag - The resistance of an object moving through air or water. As the hull or foils move through the water, drag is created. Because water is much denser than air, it creates more drag, hence lifting the boat out of the water allows it to move faster.
