AC75
The AC75 is a high-performance foiling monohull yacht class designed specifically for the America's Cup, featuring a length of 75 feet (22.86 meters), a maximum beam of 16.4 feet (5 meters), and a minimum displacement of approximately 6,500 kilograms, enabling speeds over 50 knots (93 km/h) through retractable hydrofoils that lift the hull out of the water.[1] Introduced in 2018 for the 36th America's Cup held in Auckland, New Zealand, in 2021, the class marked a shift from multihull designs to monohulls with wing-like foils, soft-wing sails (mainsail area of 145 m², jib 80 m², and code zero 180 m²), and no traditional keel, emphasizing lightweight carbon-fiber construction and self-righting capabilities for enhanced safety and speed.[2][3] The AC75 class has evolved across editions to optimize performance and inclusivity. In the 36th America's Cup, teams raced with 11 crew members powering hydraulic systems via grinders, achieving record foiling speeds while navigating tight match-racing courses.[4] For the 37th America's Cup in Barcelona, Spain, in 2024, crew size was reduced to eight, reintroducing "cyclors" (pedal-powered stations) for half the team to generate energy, alongside battery systems, which allowed Emirates Team New Zealand to defend the title against INEOS Britannia.[5] The class rules for the 38th America's Cup, scheduled for Naples, Italy, in 2027, further refine the design by limiting crews to five sailors (with at least one female required), incorporating a "guest racer" position for non-team participants, and permitting legacy hulls with updated foils to promote sustainability and broader engagement.[6][7] Key innovations of the AC75 include its three hydraulic systems for foil control, sail trim, and daggerboard adjustments, which enable precise flight dynamics and upwind performance comparable to multihulls, while the D-section mast (26.5 meters tall) supports the soft wing sail for efficient propulsion.[8][9] These yachts represent the pinnacle of yacht design, blending aerospace-inspired materials and software-driven analytics to push boundaries in speed—peaking at 55.6 knots during the 2024 Louis Vuitton Cup—and have influenced broader sailing technology despite controversies over costs and accessibility.[10][3]Development and Rule
Origins and Introduction
The AC75 yacht class was introduced as the platform for the 36th America's Cup, scheduled for 2021 in Auckland, New Zealand. Emirates Team New Zealand, as the defending syndicate following their victory in the 35th America's Cup, announced the AC75 concept on November 21, 2017, in collaboration with challenger Luna Rossa Challenge.[11][12] This marked a significant evolution in the competition's format, positioning the AC75 as a fully foiling monohull designed to push the boundaries of high-speed sailing while prioritizing safety and accessibility.[13] The decision to transition from the foiling catamarans used in previous editions, such as the AC50 class in 2017, to a monohull design stemmed from a desire to broaden participation and foster innovation within the sailing community. Grant Dalton, CEO of Emirates Team New Zealand, emphasized that monohulls would attract more quality challengers by aligning with traditional sailing preferences, as opposed to the specialized multihull expertise required for catamarans, which had limited the number of entrants in recent cycles.[14] Additionally, the shift aimed to enhance match racing tactics, improve self-righting capabilities in case of capsize, and enable more affordable technology transfers to broader yachting classes, thereby reducing overall development costs compared to the high-speed multihulls.[11] Key milestones in the AC75's development began with the announcement of the 36th America's Cup Protocol on September 28, 2017, by the Royal New Zealand Yacht Squadron and Circolo della Vela Sicilia, which outlined the framework for the event and initiated rule drafting.[15] Over the following months, Emirates Team New Zealand and Luna Rossa collaborated on the class rule, culminating in the publication of the 62-page AC75 Class Rule on March 30, 2018, ahead of the protocol's deadline.[16] This document established the foundational parameters for the foiling monohull, focusing on a 75-foot (22.86-meter) waterline length yacht capable of lifting entirely out of the water on hydrofoils to achieve exceptional speeds, thereby revolutionizing monohull performance in the America's Cup series.[17]Class Rule Specifications
The AC75 class rule, established for the 36th America's Cup in 2021, defines a high-performance foiling monohull with strict parameters to ensure fair competition and technological innovation. The yacht's overall length, including the bowsprit, is limited to 75 feet (22.86 meters), while the hull length measures between 20.600 and 20.700 meters from the transom reference plane. The maximum beam is 5 meters, and the maximum draft, with foils deployed, reaches 5 meters. These dimensions promote a lightweight, agile design capable of foiling, with the hull required to enclose a volume sufficient for flotation when foils are retracted.[16][18] Displacement is tightly controlled, with the total yacht mass, including all equipment and appendages but excluding crew, ranging from 7,470 to 7,500 kilograms to maintain parity among competitors. The rule emphasizes minimal weight for enhanced foiling performance, with the lightship displacement around 6,500 kilograms. Material restrictions mandate the use of advanced composites, primarily carbon fiber reinforced polymers for the hull, foils, and rigging, with a maximum fiber modulus of 395 GPa and density not exceeding 11,400 kg/m³ to balance strength and lightness. Permitted core materials include aluminum honeycomb, meta-aramid honeycomb, timber, and plastic foams, while high-strength metals for foil components are limited to a yield strength of 1,500 MPa. Rigging elements, such as masts and standing rigging, must comply with similar composite standards, with one-design supplied components to prevent disparities.[19][16] Crew configuration is capped at a maximum of 11 sailors, including roles dedicated to grinding for hydraulic power generation, sail trimming, and flight control to manage the yacht's high-speed foiling dynamics. Each crew member must weigh between specified limits, contributing to a total crew mass of approximately 1,000 kilograms, and all must wear safety gear including buoyancy aids and helmets. The rule prohibits non-human crew aids initially, relying on manual effort for propulsion.[19][3] Compliance is enforced by the America's Cup Measurement Committee, which verifies designs through detailed submissions including IGES files for hull and foil geometries, material certificates, and physical inspections. Tolerances are precise, such as ±5 mm for hull surface deviations, and certificates are issued only after confirming adherence to all parameters. Key constraints on stored energy systems limit elastic energy storage to 50 joules in springs or lines and restrict hydraulic accumulators to prevent unfair advantages, with batteries permitted solely for instrumentation and low-voltage systems up to 60 volts, excluding propulsion assistance in the initial class rules. These measures ensure that performance derives primarily from design ingenuity and crew skill rather than mechanical augmentation.[19][20]Evolution for Subsequent Cups
Following the 36th America's Cup in 2021, a comprehensive review led to updates in the AC75 class rules for the 37th edition held in Barcelona in 2024. The protocol governing the 37th Cup was announced on November 16, 2021, introducing key adjustments to enhance fairness and accessibility, including a strict budget cap of approximately €15 million for design and construction costs to control expenditures across teams, and a reduction in crew size to eight members to incorporate pedal-powered cyclors.[21][22] An updated Version 2 of the AC75 Class Rule was finalized on March 17, 2022, which included minor refinements to foil box dimensions, allowing limited tolerances for foil arm and wing placements within specified envelopes to balance innovation with measurement consistency.[20] These changes aimed to stabilize the class while accommodating lessons from the previous regatta, such as improved sail recut permissions and nationality requirements for crews.[21] Building on this foundation, the rules for the 38th America's Cup, scheduled for Naples in 2027, were significantly evolved and released on September 9, 2025, as Version 3.01 of the AC75 Class Rule. A core mandate requires teams to reuse legacy hulls from the 37th Cup or modified versions from the 36th, limiting new hull construction to one per team if needed, to promote continuity and reduce development costs, along with a cost cap of €75 million per team.[18][2][23] Innovations in foils were permitted through up to three new generations, including adaptations of legacy components by up to 20% within tight parameters, while propulsion systems shifted to battery-powered alternatives, eliminating the cyclor (pedaling) mechanisms used previously.[2] Additionally, crew composition was updated to a five-person sailing team with a minimum of one female athlete, fostering greater inclusivity.[2] Environmental considerations were integrated more prominently in the 38th Cup rules to minimize the event's carbon footprint. Hull reuse directly supports recycling efforts by extending the lifecycle of existing structures, while the technical regulations include incentives for using recyclable mould materials and conducting life-cycle assessments for builds, emphasizing sustainable practices in composite fabrication.[24][6] The timeline for these evolutions began with the 37th Cup protocol in late 2021 and class rule updates in 2022, followed by the 38th Cup protocol on August 12, 2025, and full rule announcements in September 2025, setting the stage for preparations in Naples.[25][2]Design Features
Hull and Structure
The AC75 hull adopts a narrow design with a wave-piercing bow to reduce wave-making resistance and facilitate rapid transitions to foiling mode.[26] The hull's lower surface is symmetric about the longitudinal center plane, extending approximately 20.6 to 20.7 meters forward from the transom reference plane, with flared sections along the perimeter line—maximum 2.5 meters from the center plane at its widest—to enhance stability during foiling while minimizing aerodynamic drag.[20] The deck layout is configured for crew operations, featuring dedicated positions for power generation, trimmers, and controllers to optimize weight distribution and operational efficiency without compromising structural integrity.[3] Structurally, the hull employs a carbon fiber composite layup with an aluminum honeycomb core for lightweight strength, cured using epoxy resins at temperatures up to 80°C, achieving a minimum areal density of 2 kg/m² and core density of at least 48 kg/m³.[27][20] Internal watertight bulkheads are positioned at more than 9 meters and between 17 to 19 meters forward of the transom reference plane, designed to withstand 10 kPa pressure and limit water flow to no more than 100 L/min in case of breach, ensuring the enclosed hull volume exceeds 60 m³.[20] For the 38th America's Cup, ballast is strictly restricted, with only 50 kg of class ballast permitted, positioned 0.75 meters forward of the forward center of buoyancy transverse reference plane, and no movable ballast beyond crew and equipment adjustments.[18] When not foiling, stability is provided by the weight of the lowered T-foils and a structural skeg along the hull bottom.[3] Safety features include multiple watertight compartments formed by the bulkheads, self-draining wet boxes for appendages (up to 300 L each for foils), and crew recovery systems comprising personal air supplies (at least 40 L uncompressed per crew member) and rescue knives (50-150 mm blades) accessible in each cockpit.[20][18]Foils and Hydrodynamics
The AC75 employs a foil configuration consisting of two primary T-shaped foils—one on each side of the hull—each comprising a canting foil arm, a horizontal foil wing, and adjustable flaps, complemented by rudder and daggerboard elements for steering and additional lift. These foils are designed as high-aspect-ratio wings to optimize hydrodynamic performance under the class rules, which specify symmetric profiles and limit flap chord lengths to no more than 50% of the wing chord at any section.[20] The overall system adheres to dimensional boxes ensuring fairness, with foil arms supplied as one-design components to control costs and uniformity.[28] Hydrodynamic principles of the AC75 foils rely on lift generation similar to aircraft wings, where the foil's airfoil shape creates a pressure differential: lower pressure over the curved upper surface and higher pressure on the flatter underside, producing upward force proportional to the square of the water flow speed and the foil's angle of attack. Flaps on the foil wings allow dynamic adjustment of this angle to maintain stable flight, while the T-configuration minimizes induced drag through efficient span loading. Ride height is controlled to approximately 2-3 meters above the water surface, reducing wave-making resistance and enabling planing-like efficiency.[29] This setup contributes to the yacht's ability to reach high speeds by lifting the hull clear of the water.[30] Foil arm mechanics incorporate canting, where each arm rotates about a longitudinal axis—up to specified angles like 7.6° inward and 119.5° outward—to optimize stability; the leeward foil cants downward for maximum lift and side force, while the windward foil raises partially out of the water to provide righting moment against heel. Raking adjustments, primarily on the rudder foil, further enhance flight stability by altering the effective angle to the flow, preventing porpoising or excessive pitch. These mechanisms are powered by crew-operated hydraulic or mechanical systems within rule limits.[20] Development of the AC75 foils presented significant challenges, including ensuring structural integrity against extreme loads during early testing, where initial one-design foil arms failed under simulated forces exceeding twice operational expectations, necessitating redesigns for enhanced carbon fiber layups and attachment points. Foil breakage risks materialized in real-world trials, such as the 2021 capsize of American Magic's Patriot, which damaged foil components due to uncontrolled loads at around 30 knots. Additionally, cavitation resistance was critical, as high-speed flow over the foils can form vapor bubbles that disrupt lift, requiring optimized profiles and surface finishes to delay inception and maintain performance.[28][31][32]Propulsion and Crew Systems
The AC75 relies on wind propulsion through its sails, with crew-generated power driving the hydraulic systems for control and adjustments. For the 37th America's Cup and later, the primary power source for onboard systems is the cyclor setup, where dedicated crew members pedal ergonomic crank systems to drive hydraulic pumps. These cyclors, typically four in number, sustain outputs of approximately 350–450 watts each during sustained efforts, enabling the boat to maintain foiling and execute maneuvers.[33][34] The pedal-driven grinders convert human effort into hydraulic pressure, powering winches and actuators without auxiliary engines, ensuring compliance with class rules mandating sail-only forward propulsion.[20] The sail plan consists of a single mainsail and jib or Code Zero headsail, designed with a wing-like profile to optimize aerodynamic efficiency in high-speed foiling conditions. The mainsail, constructed from two lightweight skins attached to a D-section mast, has a maximum area of 145 m², while the jib is limited to 80 m² and the Code Zero to 180 m², with girth measurements strictly regulated to maintain planform consistency across yachts.[1] These sails are trimmed via hydraulic sheets, allowing rapid adjustments to capture wind effectively during tacks and gybes.[20] Control systems on the AC75 integrate hydraulic rams and actuators to manage foil positioning, sheet tension, and rudder angles, all linked directly to the cyclor outputs for responsive operation. The flight control system employs rams to cant foils up to 35 degrees and adjust flaps for lift optimization, while rig controls handle mainsail and jib trimming through programmable valves and pumps operating at pressures up to 600 bar.[1][20] These self-contained hydraulic circuits ensure precise, real-time adjustments without external power, minimizing latency in high-speed sailing.[35] Crew ergonomics prioritize efficiency and safety in the demanding foiling environment, with positions divided among flight controllers, trimmers, and grinders (cyclors). Flight controllers, positioned near the helmsmen, operate joystick-like interfaces to monitor and adjust foil rake and ride height, drawing on real-time data from onboard sensors. Trimmers, located forward of the cyclors, fine-tune sail sheets and mainsail twist to balance power and stability. Grinders occupy aft cockpits, pedaling in synchronized pairs to sustain hydraulic pressure, with ergonomic seating and harnesses designed to reduce fatigue during prolonged efforts up to 20 minutes.[1][36] For the 38th America's Cup, rules transition from full cyclor reliance to battery-assisted systems, providing stored energy equivalent to four cyclors (baseline 1200 W, peak up to 3000 W) while constraining total energy storage to 15 kWh in a standardized primary battery bank.[18]Yachts and Teams
List of AC75 Yachts
The AC75 class was first introduced for the 36th America's Cup in 2021, with teams constructing prototype boats in late 2019 for initial testing and development, followed by race-ready second-generation yachts launched primarily in 2020 ahead of the Auckland regatta. These initial prototypes allowed teams to validate foiling systems and hydrodynamics, while the full fleet of race boats was completed by early 2021. Builders included specialized composite facilities in team home countries, such as Core Composites in New Zealand for Emirates Team New Zealand and a dedicated site in Bristol, Rhode Island, for American Magic. Many of these 36th Cup yachts were later repurposed for training or development ahead of subsequent events, with some remaining active into the mid-2020s.[37][38] For the 37th America's Cup in 2024, teams were limited to one new AC75 per protocol to control costs, with launches concentrated in early 2024 in preparation for the Barcelona regatta. Builders continued to leverage advanced composites expertise, including Carrington Boats in the UK for INEOS Britannia. Post-2024, most 37th Cup AC75s remain active, as the protocol mandates their reuse (or designs derived from them) for the 38th America's Cup scheduled for 2027 in Naples, Italy, with ongoing maintenance and modifications for youth, women's, and open divisions, though NYYC American Magic withdrew from the event on October 28, 2025.[10][39][40][41]| Team | Yacht Name | Builder | Launch Date | Status |
|---|---|---|---|---|
| Emirates Team New Zealand (NZL) | Te Rehutai | Core Composites (New Zealand) | November 19, 2020 | Repurposed for training and testing through 2024; stored post-37th preparations |
| INEOS Team UK (GBR) | Britannia | Carrington Boats (UK) | October 4, 2019 (prototype); second-generation October 17, 2020 | Repurposed for development; elements integrated into 37th Cup successor |
| Luna Rossa Prada Pirelli (ITA) | Luna Rossa AC75 | Persico Marine (Italy) | October 2, 2019 (prototype); second-generation in October 2020 | Retired after 36th; successor built for 37th |
| NYYC American Magic (USA) | Defiant | American Magic facility, Bristol, RI (USA) | September 15, 2019 | Repurposed for testing; transitioned to 37th Cup boat |
| Emirates Team New Zealand (NZL) | Taihoro | Core Composites (New Zealand) | April 12, 2024 | Active; winner of 37th America's Cup; preparing for 38th |
| INEOS Britannia (GBR) | Britannia | Carrington Boats (UK) | April 20, 2024 | Active; challenger finalist in 37th; preparing for 38th |
| Luna Rossa Prada Pirelli (ITA) | Luna Rossa AC75 | Persico Marine (Italy) | April 13, 2024 | Active; Louis Vuitton Cup semi-finalist in 37th; preparing for 38th |
| NYYC American Magic (USA) | Patriot | American Magic facility, Portsmouth, RI (USA) | May 7, 2024 | Active in 37th; team withdrew from 38th America's Cup on October 28, 2025 |
| Alinghi Red Bull Racing (SUI) | BoatOne | Alinghi facility (Switzerland/Spain) | April 16, 2024 | Active; preparing for 38th after 37th participation |
| Orient Express Racing Team (FRA) | Orient Express AC75 | Multi-site collaboration (France/Spain) | May 28, 2024 | Active; debut team in 37th; preparing for 38th |