A Bold Venture at the Cutting Edge of Innovation
Commissioned as a regional flagship by Provence-Alpes-Côte d’Azur, the PACA foiling trimaran embodied both the visionary momentum of French offshore sailing in the 1980s and the technical volatility inherent to pioneering prototypes.
Designed by Gilles Vaton and skippered by Paul Ayasse, this maxi trimaran was engineered for blistering performance, achieving remarkable bursts of speed that hinted at its untapped potential.
Though its operational life proved brief, the vessel’s daring architecture and fleeting brilliance warrant a closer look at its singular journey.
Specifications
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- MAXI FOILER “PROVENCE-ALPES-CÔTE D’AZUR” (PACA)
- LOA: 77.45 ft
- LWL: 74.15 ft
- MAX BEAM (main hull): 12.83 ft
- WATERLINE BEAM (main hull): 8.01 ft
- OVERALL BEAM: 67.58 ft
- LIGHT DISPLACEMENT: 9.25 long tons
- MAX DISPLACEMENT: 10.00 long tons
- WETTED SURFACE AREA (half load): 455.13 sq ft
Project Genesis
A Regional Ambition Driven by Innovation
The PACA project originated from an initiative by the Regional Council of Provence to assert its presence in the competitive world of offshore sailing, following the example of other territories such as Charente-Maritime. Drawing inspiration from the performance of the foiler “Charles Heidsieck”, the vessel was conceived to merge cutting-edge naval engineering with regional representation.
Despite initial discussions favoring a catamaran, the final decision endorsed a foil-equipped trimaran, approved by Gaston Deferre in 1984. The design, supported by computational fluid dynamics and structural analysis performed on a CRAY 1 supercomputer by the CEA, led to a lightweight epoxy composite structure.
Early sea trials confirmed the platform’s exceptional potential: sustained speeds exceeding 30 knots, remarkable pitch stability in heavy seas, and partial lift-off under sail. Even with a provisional aluminum mast, the vessel exhibited extraordinary velocity, hinting at even greater performance with a refined carbon wing rig.
Compared to the conventional multihulls of its era, the PACA foiler stood out as a true racing machine—decades ahead of its time in both concept and execution.
GENERAL DESIGN
With the first foiling trimaran built—TABARLY’s Paul RICARD—and the second, CHARLES HEIDSIECK, a new generation of sailing Formula Ones emerged, achieving minimal water contact compared to conventional catamarans.
The core principle of the foiler is to employ a leeward foil to provide both dynamic stability and lateral resistance.
The original concept behind the new MAXI FOILER PROVENCE-ALPES-CÔTE D’AZUR, alongside CHARLES HEIDSIECK, was to pioneer partial lift across the entire platform through several integrated effects:
• Employ a lifting foil to counteract the lateral forces of the rig, replacing hull immersion and Archimedean displacement, thereby reducing drag and significantly decreasing wetted surface area.
• Utilize the crossbeam connecting the main hull and outrigger as a lift-generating structure, exploiting static pressure created by airflow deceleration within a divergent-convergent nozzle formed between the underside of the beam and the water surface.
• Design a central hull distinct from conventional multihulls, shaped to harness high-speed flow for dynamic lift and planing, featuring subtly reversed aft sections.
• Integrate an inflatable wing mast and sail system delivering greater aerodynamic power per unit area than traditional battened sails.
• Achieve a highly centralized longitudinal balance by positioning the mast/sail drive and crossbeam further aft.
• Minimize aerodynamic drag across the entire trimaran. This partial lift configuration reduces wetted surface (already lower than on catamarans), eliminates pitching motion, and enhances the efficiency of the sail powertrain.
This semi-lift architecture enables reduced wetted area, pitch suppression, and improved sail performance.
For the PACA platform, exceptional lightness and structural rigidity were achieved through carbon-epoxy composite construction, optimizing foil and beam efficiency.
Future iterations will push lift even further, with hulls barely skimming the surface—approaching full hydrofoil mode.
LATERAL AND CENTRAL FOILS
The relative positioning of the lateral foils and the sail plan is critical—firstly, as on conventional yachts, to ensure helm balance, and secondly, to regulate foil immersion.
For proper helm balance, the aerodynamic thrust from the sail must be equal and opposite to the hydrodynamic lift generated by the leeward foil, referenced to a horizontal plane. Since sail thrust acts forward, the foils are positioned ahead of the sail center of effort.
By placing the rig directly above the vessel’s center of gravity from the outset of the design phase, the foil and crossbeam positions are naturally derived, resulting in optimal longitudinal trim.
Managing the leeward foil’s depth is a delicate task. Ideally, the outrigger hull should be immersed to approximately 200 mm (7.87 inches) to prevent ventilation of the foil’s upper surface, particularly at speeds between 20 and 30 knots.
If, in a plane perpendicular to the vessel’s axis, the vertical component of sail thrust is excessive, the foil may breach the surface, ventilate, and cause the boat to skid. Conversely, if the foil’s lift drives the outrigger deeper until equilibrium is restored, performance suffers—but this is the lesser evil. A safety margin is incorporated to account for the difficulty in pinpointing the sail’s exact center of pressure. The leeward foils are dimensioned for an average lift of 5 tonnes (11,023 lbs) at 20 knots, and up to 10 tonnes (22,046 lbs) at 25 knots.
Foils are positioned forward of the center of buoyancy to counteract pitching through a slight bow-up attitude.
The aft foil—referred to as the “stingray wing”—is mounted far aft in an inverted V configuration, providing 1.5 tonnes (3,307 lbs) of lift at the stern. This compensates for bow-up trim at speed and effectively suppresses pitching, eliminating any pendulum-like motion.
With longitudinal stability ensured, the lateral foils operate more efficiently. The vertical fin of the aft foil provides directional stability and anti-drift control, while the lateral foils drive lift at the forward-midsection. On downwind points of sail, the vessel maintains a straight track, recovering energy typically lost to yaw and leeway,
resulting in precise course-keeping and responsive helm control.
This “keel” also serves as impact protection for the rudder (from debris, wreckage, etc.). Finally, the overall configuration and 45° foil geometry enable dynamic self-stabilization—akin to an autogyro in flight.
HIGH-LIFT CROSSBEAM DESIGN
The concept behind the wing-shaped crossbeam is to maximize lift generated by the lower surface (intrados) through ground effect. The “nozzle” is formed by the underside of the winged beam, the water surface, and the inner sides of the outriggers. This configuration draws directly from aeronautical engineering and constitutes a case of “enhanced ground-effect lift.”
The objective is to define a profile that delivers the highest possible lift coefficient (Cz) without compromising drag. The beam’s vertical thickness remains less than its chord length. The key advantage of this configuration lies in its high aerodynamic efficiency—expressed as the ratio between lift coefficient (Cz) and drag coefficient (Cx). The primary unknown remains its behavior in short, choppy seas.
Assumptions:
• The flow is steady, two-dimensional (with outriggers, lateral foils, and central hull approximating infinite aspect ratio), and turbulent.
• Air is treated as incompressible (maximum design velocity: 40 m/s ≈ 78 knots or 144.3 ft/s).
• Flow divergence increases. Two scenarios are considered:
- Approach of the intrados to the undisturbed streamlines at infinity: this is the “ground effect.” The water surface acts as a non-deforming streamline, effectively simulating the infinite flow condition. In practice, proximity to the surface reduces upstream divergence and enhances downstream convergence of the streamlines along the intrados. The combination of these two phenomena results in enhanced ground-effect lift.
- Lift coefficient (Cz) being proportional to camber suggests selecting a pre-cambered base profile, such as Göttingen No. 652. The expected upward thrust should reach approximately 1.5 tonnes (3,307 lbs) under 30–40 knots of apparent wind.
- Aerodynamic design process: Based on the design brief specifying desired lift, drag, and moment coefficients, the aerodynamicist will determine the pressure distribution across the wing, accounting for the plate effect of the outrigger hull. These pressure parameters feed into a computational fluid dynamics program that calculates the profile coordinates according to fluid mechanics laws.
- Once external shapes are defined, structural volume optimization follows—calculating the beam’s internal structure to withstand mechanical loads, particularly righting moments. The beam will be constructed from carbon-epoxy and Nida core, with finite element analysis performed by CEA Cadarache.
- Compared to CHARLES HEIDSIECK, where only the leading-edge half of the profile was load-bearing (the aft section serving merely as fairing), the new design adapts the entire profile to structural duty. This approach is expected to yield a weight saving of approximately 1,100 kg (2,425 lbs) over the previous system.
WING MAST AND INFLATABLE SAIL SYSTEM
The conventional multihull rig—comprising jib, rotating mast, and full-batten mainsail with pronounced roach—is poorly suited to the high speeds now achievable. Excessive drag, low aerodynamic efficiency, difficult and hazardous maneuvers due to the roach, and fragile sail materials all compromise performance. Our mainsail will be as rectangular as possible.
Efficiency ratings (on a scale from 1 to 10), based on comparative aerodynamic formulas at equal surface area, are as follows:
- 1.7: conventional sails + fixed mast
- 1.8: conventional sails + rotating mast
- 2.4: thick sails + rotating mast
- 2.8: thick sails + rotating mast + slot effect
- 5.0: rotor + boundary layer suction
Selected configuration: thick sails + rotating mast + slot effect, with optional lightweight genoa for light air conditions.
The wing mast design is based on the NACA 65 A 015 profile. Given a maximum righting moment of 70,000 m/kg (505,750 ft·lbf), mast compression is estimated at 42.4 tonnes (93,500 lbs), with 60 tonnes (132,300 lbs) absorbed by the crossbeam, lateral stays, and forestay. The mast may be fabricated from existing profiles or extruded in two sections.
Regarding the sail plan, we opted from the outset for an inflatable, non-rigid configuration: reduced weight and simplified handling are essential. The original concept involves a central membrane derived from a conventional sail (without roach), flanked by two sealed fabric chambers occupying 50% of the chord on either side.
Upon reviewing the project, ZODIAC proposed a fully inflatable thick sail system (jib + mainsail) pressurized by apparent wind, with inflation achieved via two scoops at the sail heads. The profile is shaped by internal batten sleeves.
It is worth noting that this wing mast + inflatable sail system is particularly well-suited to multihulls, which exhibit minimal abrupt motion—critical for the stability of such a sophisticated sail engine. The overall multi-point lift architecture further reinforces the viability of this concept.
CENTRAL HULL AND OUTRIGGERS
Modern multihull hulls tend to resemble tubes more than fully balanced hull forms along their length. The prevailing design philosophy suggests that ultra-fine hulls exhibit virtually no speed limitations in terms of drag.
However, such hulls suffer from two major drawbacks: first, any additional load significantly increases wetted surface due to vertical topsides; second, their long and narrow geometry offers no reduction in wetted area with increasing speed.
We opted for a hull form that, at equal length, retains the speed potential of tubular hulls but transitions smoothly and horizontally with flow acceleration. The forward section features a deep-V profile, unlike the U-shaped bow of CHARLES HEIDSIECK. Wetted surface reduction along the topsides and stem becomes rapidly effective, especially as increased speed enhances foil lift and reduces drag through overall weight relief—creating a virtuous cycle.
Initially, the primary advantage of this configuration lies in the reduced wetted surface. With a LWL of 22.60 m (74.15 ft) compared to 23.00 m (75.46 ft) for the catamaran “FORMULE TAG”, we achieve just 42 m² (452 ft²) versus 79 m² (850 ft²) for “TAG”.
The leeward foil occupies a surface area barely exceeding that of the daggerboard and rudder appendages found on conventional catamarans or trimarans. The sail area-to-wetted surface ratio becomes exceptional for the MAXI FOILER PROVENCE-ALPES-CÔTE D’AZUR: 5.42 m² (58.34 ft²) versus 2.91 m² (31.32 ft²) for “TAG”—despite a reasonable sail area-to-displacement ratio of 25.5 m²/t (276 ft²/LT), thanks to the efficiency of the inflatable sail system.
Another key advantage is the complete absence of leeway on the MAXI FOILER, unlike catamarans whose hulls and appendages generate additional drag from the aft third of both hulls and their daggerboards. This contributes to their inability to point high into the wind, compounded by violent pitching.
As for the outriggers, we limited their total volume to 5 m³ (176 ft³) each, yielding a length of 12.000 m (39.37 ft). This minimizes wave impact and prevents torsional stress on the crossbeam. The 5 m³ volume is supplemented by the half-volume of the crossbeam, rendering the MAXI FOILER virtually uncapsizable.
STABILITY AND LOAD ASSESSMENT
Lateral stability, achieved through a beam of 23.00 m (75.46 ft), is substantial: the maximum righting moment is estimated at 70,000 mkg (505,750 ft·lbf).
Longitudinal stability has been carefully managed through optimal weight distribution, starting with the 900 kg (1,984 lbs) wing mast/sail drive positioned directly over the vessel’s center of gravity. The crossbeam’s center of mass is located aft of this general CG, at 2,050 kg (4,519 lbs).
LATERAL FOILS
Lift under optimal surface conditions
Speed: 10 knots — Lift: 1,110 kg (2,447 lbs)
15 knots: 2,720 kg (5,997 lbs)
20 knots: 5,160 kg (11,379 lbs) — Average stability moment: 60,372 mkg (437,000 ft·lbf)
25 knots: 8,480 kg (18,700 lbs)
30 knots: 12,680 kg (27,960 lbs)
35 knots: 17,650 kg (38,920 lbs)
Effective surface area: 2.54 m² (27.34 ft²) at 45° dihedral
Modified NACA 16.80.28 profile designed to:
• Deliver optimal and consistent performance across the entire foil span
• Feature a flat intrados from 10% to 100% chord for simplified manufacturing
• Generate 5 tonnes (11,023 lbs) of lift normal to the foil at zero angle of attack at 20 knots (minimal drag)
• Prevent cavitation across a wide range of speeds and angles of attack (avoiding vibration, erosion, and structural fatigue)
• Ensure even stress distribution for improved material resistance and extended service life
• Guarantee reliability through SNIAS (AEROSPATIALE/HELICO) manufacturing
• Maintain a flawless surface finish for enhanced lift
• Offer competitive cost including fittings
• Position strut attachment point 0.30 m (11.8 in) aft of the foil’s leading edge
• Require precise assembly to verify zero angle of incidence
STINGRAY FOIL
Lift under optimal surface conditions
Speed: 10 knots — Lift: 260 kg (573 lbs)
15 knots: 1,200 kg (2,646 lbs)
20 knots: 1,972 kg (4,349 lbs)
Effective surface area: 1.5 m² (16.15 ft²)
Improvement: review and refine mounting bracket profiles
At 20 knots
Leeward foil: 5,160 kg (11,379 lbs)
Windward foil: 1,500 kg (3,307 lbs)
Stingray foil: 1,200 kg (2,646 lbs)
Total lift: 7,860 kg (17,332 lbs)
At 25 knots
Leeward foil: 8,480 kg (18,700 lbs)
Windward foil: 1,700 kg (3,748 lbs)
Stingray foil: 1,972 kg (4,349 lbs)
Total lift: 12,152 kg (26,797 lbs)
Suggested improvement at 10 knots — Foil lift
———— 1.6 tonnes (3,527 lbs) (+10% and increased camber)?
