At more than 50 knots, there is very little room for hesitation. An AC75 balances on a foil wing beneath the water while enormous aerodynamic loads build in the double-skinned mainsail above it. Sailors ask for changes to sail shape, foil settings and mast controls constantly, often in tiny increments, sometimes several times within seconds.
Between the sailor making that request and the hardware responding sits one of the least visible but most important pieces of technology aboard an AC75: the Programmable Logic Controller. Sailors just call it "the PLC."
In simple terms, it is an extremely fast, robust industrial computer. It receives commands, processes them according to its programmed logic, and sends instructions on to the systems that make things move. On an AC75 it forms a critical part of the electronic architecture controlling the yacht.
The sailors provide the intelligence and tactical decisions. Hydraulic pressure supplies the muscle. The PLC connects the two, acting as the digital nervous system of an America's Cup yacht.
Watch a sailor working inside the cockpit and many of the inputs look surprisingly small. Buttons, paddles, rotary controls and switches allow for extraordinarily precise adjustments, but behind those controls lies a complex electronic and hydraulic chain. Commands travel through the control system, where software interprets the request before the appropriate hydraulic actuator moves a component by the required amount.
Thousands of lines of code can sit between a sailor pressing a button and the correct actuator moving at the correct speed. During the previous Cup cycle, the British team described the process as "a web of wiring, processors and electronics translating crew inputs into precise hydraulic movement." Precision really is everything. A large unintended movement at 45 or 50 knots could be disastrous. Equally, a control system that is too slow, inaccurate or inconsistent will simply make the yacht slower.
Programmable Logic Controllers are not unique to sailing. They were developed for industrial automation and turn up controlling manufacturing machinery, production lines and complex mechanical processes the world over. They are designed to run continuously, process multiple inputs and outputs extremely quickly and, crucially, remain reliable.
Reliability aboard an America's Cup yacht is particularly hard won, which is why teams spend countless hours on the water refining and advancing their PLC outputs.
The electronics on an AC75 operate amid salt water, vibration, enormous structural loads, heat and constant shock, all aboard a platform travelling at motorway speeds while repeatedly accelerating and decelerating. The AC75 adds another layer of complexity because its electronics must interact with exceptionally powerful hydraulic systems. Luna Rossa has previously described the AC75 as a mechatronic system, one where industrial computers sit between the sailors and hydraulic actuators operating at pressures that can reach around 600 bar.
That combination of mechanical engineering, electronics, hydraulics and software is one of the defining technologies of the modern America's Cup, and the ultimate battleground for the teams.
There are several major electronic and control architectures aboard the yacht. Historically these have included the Foil Cant System, instrumentation and logging systems, crew information systems and electronic control circuits governing hydraulic functions, four areas Luna Rossa described during the first generation of AC75 development.
The Foil Cant System offers a useful illustration of what a PLC can actually do. The AC75's enormous foil arms have to move between their lowered foiling position and raised position during manoeuvres. In development of the original one-design Foil Cant System, Emirates Team New Zealand used a Beckhoff PLC alongside the motor controller, hydraulic pump, accumulator and cylinders.
The system had to control an enormous moving mass smoothly while managing the oscillations generated by the foil arm and wing. The PLC could be tuned to make that movement smooth and controlled rather than simply commanding an actuator to move from one position to another. This is control engineering rather than conventional yacht mechanics, and it happens repeatedly around the boat.
Which is partly why software engineers have become such important members of modern Cup design teams. The hardware provides the capability; software determines how effectively that capability gets exploited. The system needs to recognise an input, determine what action is permitted, translate that request into a command, communicate with the relevant hardware, and make the adjustment accurately. Small improvements in latency, accuracy, repeatability or control quality can translate directly into better sailing performance.
For the Louis Vuitton 38th America's Cup, the importance of electronic management has increased again. One of the major changes for the 2027 AC75 is the removal of the cyclors used during the 37th America's Cup. Instead, the AC75 will run on stored, and limited, electrical energy.
A specified one-design battery arrangement forms the primary battery bank supplying energy for the yacht's moveable systems, while the rules allow teams considerable freedom in developing their control systems, hydraulics and electronics within the existing hull architecture. The official AC75 specification describes the lithium battery system as driving the hydraulics and powering the PLC, with the PLC managing sail, mast and board controls. That represents a profound change inside the boat.
The hulls themselves are being reused, adapted from previous campaigns, but much of the development battle has shifted beneath the surface into foils, systems and electronic management. As Emirates Team New Zealand Chief Designer Dan Bernasconi noted when the AC38 rules were published, analysis of the AC37 yachts suggested the differences between hull shapes were relatively small, while the major gains were being found in foils and systems. For 2027, that puts even greater weight on the engineers working on the parts of the yacht nobody sees.
Much of America's Cup development can be seen. New foil shapes attract recon photographers the moment they come out of the team bases. Sail configurations get analysed from chase boats. Rudders, aero treatments and modifications are scrutinised almost as soon as a yacht leaves the shed.
The PLC is different.
Most of its performance is invisible. You cannot stand on the dock and photograph an algorithm, and you cannot easily tell how efficiently another team's control architecture processes an input, or how accurately its hydraulic system reproduces a sailor's command. Yet these areas may hold some of the most valuable performance gains of the entire campaign.
That is why mechatronics, electronics and software engineers have become every bit as embedded in Cup design teams now as naval architects, aerodynamicists and structural engineers. The modern AC75 is still a sailing yacht, and the wind remains its engine. The sailors still have to start well, find the shifts, execute the manoeuvres and race the opposition, but between their fingertips and the most powerful moving systems aboard the yacht sits an extraordinarily sophisticated layer of electronics, software and control engineering.
The Programmable Logic Controller sits at the heart of that world. Small, largely unseen, and operating continuously beneath the deck, it helps turn human intention into precise mechanical movement.
At more than 50 knots, that movement needs to be close to perfect. In the modern America's Cup, speed is no longer just about generating power. Increasingly, it is about controlling it.
