INSIDE THE AC75: THE PROGRAMMABLE LOGIC CONTROLLER – THE BRAIN BEHIND THE MACHINE

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, or as the sailor’s call it – “the PLC.”

In simple terms, the PLC is an extremely fast, robust industrial computer. It receives commands, processes them according to its programmed logic and sends instructions onwards to the systems that make things move. On an AC75 it forms a critical part of the electronic architecture controlling the yacht. The sailors may provide the intelligence and tactical decisions, while hydraulic pressure supplies the muscle, but the PLC helps connect the two. Welcome to the digital nervous system of an America's Cup yacht.

FROM BUTTON TO MOVEMENT
Watch an AC75 sailor working inside the cockpit and many of the inputs look surprisingly small. Buttons, paddles, rotary controls and switches allow sailors to request extraordinarily precise adjustments. Behind those controls, however, lies a complex electronic and hydraulic chain. The sailing team operates the yacht through electronic input devices. Those 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 and by the required amount. 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 is everything as 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. The PLC has to execute commands repeatedly, rapidly and reliably in an extraordinarily hostile environment.

INDUSTRIAL TECHNOLOGY
Programmable Logic Controllers are not unique to sailing. PLCs were developed for industrial automation and can be found controlling manufacturing machinery, production lines and complex mechanical processes around the world. They are designed to operate continuously, process multiple inputs and outputs extremely quickly and, crucially, remain reliable. Reliability aboard an America's Cup yacht is particularly challenging and key to success and is why teams spend countless hours on the water refining and advancing their PLC outputs.

The electronics on an AC75 are operating in an environment involving salt water, vibration, enormous structural loads, heat and constant shock, all onboard 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 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.

CONTROLLING AN AC75
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. Luna Rossa described these four areas during the first generation of AC75 development. The Foil Cant System provides a particularly good illustration of what a PLC can do with the AC75's enormous foil arms having 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 therefore be tuned to help 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.

This is also why software engineers have become such important members of modern America's Cup design teams. The hardware may provide the capability, but software determines how effectively that capability can be exploited. The system needs to recognise an input, determine what action is permitted, translate that request into an appropriate command, communicate with the relevant hardware and make the adjustment accurately. Small improvements in latency, accuracy, repeatability or control quality can translate into better sailing performance.

A NEW ERA
For the Louis Vuitton 38th America's Cup, the importance of electronic management has increased still further. 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 use 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 the development of 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 and that represents a profound change inside the boat.

The physical hulls themselves are being reused albeit adapted from previous America's Cup campaigns, but much of the development battle has moved 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 that differences between the hull shapes were relatively small, while the major gains were being found in foils and systems. For 2027, that places even greater emphasis on the engineers working on the invisible parts of the yacht.

THE INVISIBLE DESIGN WAR
Much of America's Cup development can be seen. New foil shapes attract recon photographers immediately as they come out of the team bases. Sail configurations can be analysed from chase boats. Rudders, aero treatments and modifications are scrutinised almost immediately after a yacht leaves the shed. The PLC and the software surrounding it are different and most of their performance is invisible. You cannot stand on the dock and photograph an algorithm, and you cannot easily determine how efficiently another team's control architecture processes an input or how accurately its hydraulic system reproduces a sailor's command and yet these areas may contain 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 America's Cup design teams 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 some of 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 virtually perfect because in the modern America's Cup, speed is not simply about creating power. Increasingly, it is about controlling it.