As a purebred sport catamaran, the Diam 3 eschews any form of interior accommodations or cruising amenities. There are no cabins, joinery, or galley installations; instead, the "living space" is a high-tension mesh trampoline stretched between two ultra-slim hulls and rigid aluminum crossbeams. Every aspect of the boat's physical makeup is dedicated to weight reduction, structural rigidity, and aerodynamic efficiency.
Sailing Performance & Handling
At the heart of the Diam 3’s appeal is its explosive performance, governed by a light displacement of just 400 pounds (180 kg) and an aggressive sail plan. Its upwind sail area of 228 square feet yields a Sail Area to Displacement ratio (SA/Disp) of 66.9. In physical terms, this translates to instant, highly sensitive acceleration and the ability to fly the windward hull in even the lightest of breezes. Downwind, the deployment of a 226-square-foot asymmetric spinnaker expands the total sail area to 409 square feet, requiring intense coordination between the helm and crew to maintain optimal footing and stable apparent wind angles.
The boat’s Capsize Ratio of 4.63 highlights the inherent dynamics of its high-performance multihull design. Boasting an overall beam of 8 feet 6 inches, the Diam 3 offers immense lateral stability. However, in sport catamarans, this stability shifts the primary capsizing threat from rolling over to pitchpoling (or "cartwheeling") downwind. To prevent the narrow bows from digging into the back of waves under spinnaker, the crew must utilize the dual trapezes to shift their body weight as far aft as possible.
Steering is managed via twin semi-spade rudders controlled by a single tiller, providing an incredibly direct, low-drag helm feel. Lift is generated by highly efficient twin daggerboards. Dropping the daggerboards provides a maximum draft of 3 feet 1 inch, allowing the boat to point aggressively close-to-wind. When sailing downwind or approaching a beach, the boards can be retracted, reducing the draft to mere inches. To squeeze every knot of performance out of the fractional sloop Marconi rig, the crew must actively manage the rotating wing mast, ensuring the mast rotator is continuously adjusted relative to the wind angle to maintain a clean aerodynamic flow across the mainsail.
Market Snapshot & Economics
On the used market, the Diam 3 represents an exceptional, budget-friendly entry point into the world of high-performance catamaran racing. Because it is an early to mid-generation F18 design, it trades at a significant discount compared to modern, carbon-foiling catamarans or newer F18 platforms like the Nacra Evolution or Exploder. The boat occupies a highly functional niche for sailors who want maximum speed and technical engagement per dollar.
Inventory is relatively scarce and primarily concentrated in European coastal regions (specifically France) and select Caribbean multihull hubs where ADH Inotec maintained its strongest footprints. Because beach catamarans are highly exposed to the elements and subjected to extreme physical loads, the purchase price of a used Diam 3 is often secondary to the condition of its sails, mast, and fiberglass hulls. Buyers should expect the economics of ownership to revolve around rigging replacement, sail inventory updates, and trailer maintenance rather than traditional yacht refit costs.
Known Issues & Triage
Because the Diam 3 was built using a sandwich foam fiberglass polyester (GRP) construction to keep weight at the F18 minimum, checking the structural integrity of the hulls is the first order of business during any pre-purchase inspection. Over years of hard racing and beach landings, these platforms can develop specific stress points:
- Hull and Deck Soft Spots: Constant high-tension hiking and crew movement can cause the sandwich foam core to delaminate from the fiberglass skin. Common culprits include the decks directly adjacent to the shroud chainplates and the areas where the crew stands while on the trapeze. Soft spots must be addressed via epoxy injection or localized recoring to restore structural stiffness.
- Crossbeam Connection Play: The structural integrity of a catamaran relies on the rigid connection between the aluminum crossbeams and the GRP hulls. Under the high loads of a tight rig, the beam self-tapping screws or mounting bolts can flog out their holes, leading to platform twist. Inspecting these joints for hairline fractures in the gelcoat or physical play is a critical triage step.
- Daggerboard Trunk Wear: Constant raising and lowering of the high-aspect daggerboards can wear down the internal carpet or neoprene shims inside the daggerboard trunks. This wear introduces play, allowing the boards to vibrate or shift under load, which degrades aerodynamic lift and helm responsiveness. Replacing these protective shims is a common, necessary DIY maintenance item.
Modernization & Upgrades
As older F18 platforms have aged, a vibrant community of catamaran enthusiasts has developed standard upgrade paths to keep boats like the Diam 3 competitive in open handicap fleets:
- Decksweeper Mainsails: The most significant aerodynamic modernization for mid-generation F18s is the retrofitting of a "decksweeper" mainsail. By extending the foot of the sail down to seal the gap against the trampoline, the sail capitalizes on the "end-plate effect," drastically reducing drag, increasing vertical lift, and boosting top-end speed.
- High-Ratio Mainsheet Systems: Original mainsheet blocks are often upgraded to modern 10:1 or 12:1 purchase systems using low-friction carbo blocks. This upgrade reduces the extreme physical strength required to trim the square-top mainsail in heavy air, allowing for more precise, rapid adjustments on the course.
- Snuffer System Overhauls: Early spinnaker retrieval systems can be clumsy. Modernizing the bow-mounted spinnaker snuffer with a high-capacity ring hoop and a slick, low-friction bag reduces retrieval friction, preventing expensive sail tears during fast, downwind douses.
The Verdict
The Diam 3 is a highly technical, uncompromising speed machine designed for sailors who prioritize raw performance and physical engagement over comfort. While it lacks the versatility of a cruising boat, it rewards its crew with thrilling speeds, precise handling, and an affordable gateway into one of the most competitive multihull classes in the world.
Pros
- Exceptional power-to-weight ratio offering thrilling, high-speed sailing.
- Rigid, high-quality GRP sandwich construction designed by Bertrand Desjoyeaux.
- Versatile twin daggerboard design allows for deep windward tracking and easy beaching.
- Highly accessible entry price point into the Formula 18 racing class.
Cons
- Completely lacks interior accommodations, protection from the elements, or storage.
- Physically demanding to sail, requiring two experienced crew members on dual trapezes.
- Higher risk of pitchpoling downwind compared to more modern, volume-forward hull designs.
- Used inventory is limited and highly concentrated in specific European and Caribbean locales.
