Aquarius Arc-21 Information, Review, Specs

The vessel is constructed with a focus on a high strength-to-weight ratio, typically utilizing vacuum-bagged foam cores and fiberglass reinforcements, though carbon fiber enhancements have been used in various production iterations. As an open-cockpit performance boat, it lacks the interior accommodations of a cruising vessel, focusing entirely on the "platform" experience—a trampoline-based living and working space designed for maximum crew efficiency during high-speed transitions. The design's longevity is a testament to the partnership between Bill Roberts Catamarans and Aquarius Sail, emphasizing a "one-design" philosophy that ensures the boat remains competitive in open-class racing decades after its inception.

Sailing Performance & Handling

The sailing characteristics of the ARC-21 are defined by its exceptional righting moment and aerodynamic efficiency. Because the boat carries an 8' 6" beam on a 21-foot hull, it offers a stable platform that allows the crew to keep the boat flat and accelerate quickly in light air. According to technical specifications from Aquarius Sail, the boat features a 33-foot mast, providing a massive sail area-to-displacement ratio that places it in the top tier of beach catamarans.

The handling is noted for its precision, largely due to the oversized, high-aspect rudders and the absence of a traditional boom on many configurations, which allows for a cleaner airflow over the lower portion of the mainsail. The self-tacking jib is a critical feature for short-handed sailing or intense racing, allowing the crew to focus on weight distribution and mainsheet trim during tacks rather than managing jib sheets. Owners frequently report that the boat tracks exceptionally well upwind, "pointing" higher than many of its contemporaries in the 20-foot class. In heavy air, the ARC-21’s hull shape—characterized by fine entries and sufficient volume forward—is designed to resist "pitch-poling," a common hazard for high-performance multihulls.

Popular Mentions & Media

While the ARC-21 does not occupy the same mainstream space as the Hobie Cat, it has a dedicated following in the world of long-distance catamaran racing. The model and its variants are frequent participants in endurance events like the Tybee 500 and various Great Lakes distance races. The design philosophy of Bill Roberts, specifically his focus on "unstayed" mast concepts and drag reduction, has been featured in technical sailing journals and was a subject of discussion in the development of high-speed multihull theory during the late 20th century.

Known Issues & Buyer’s Checklist

Purchasing a used ARC-21 requires a focused inspection of the high-stress areas inherent to performance catamarans.

• Daggerboard Trunks: Given the high lateral loads generated by the deep daggerboards, the trunks should be inspected for stress fractures or delamination at the hull-to-trunk interface.
• Beam Bolts and Sockets: The ARC-21 uses a robust beam-to-hull connection to maintain rigidity. Potential buyers should check for "working" (movement) in these joints, which can lead to elongated bolt holes or spiderweb cracking in the gelcoat.
• Mast Step and Rotation: The rotating mast puts significant pressure on the mast step. Ensure the bearing surfaces are smooth and the step itself is not showing signs of compression into the main beam.
• Trampoline and Rigging: Due to the high tension required for the rig, the forestay chainplates and the trampoline tracks should be checked for lifting or corrosion. The trampolines themselves are high-wear items and can be expensive to replace given the custom nature of the ARC line.
• Rudder Kick-up Mechanism: The high-aspect rudders exert significant leverage on the kick-up housings. Check for slop or play in the rudder pintles and gudgeons, as this will directly impact the boat’s legendary "feel" at the helm.

Community & Resources

The ARC-21 benefits from a niche but highly technical community. Aquarius Sail Inc. remains the primary repository for technical data and replacement parts, continuing to support the fleet from their facility in Minnesota. While there is no longer a dedicated "class association" with the bureaucracy of Olympic classes, the "SuperCat" and "ARC" owners often congregate on technical forums to share tuning guides and repair tips. The designer’s legacy is maintained through the Bill Roberts Catamarans technical archives, which provide insight into the specific hydrodynamic choices made for the 21-foot hull.

The Verdict

The Aquarius ARC-21 is a specialist’s tool, designed for the sailor who prioritizes raw speed and technical refinement over simplicity. It remains one of the fastest "trailer-legal" boats on the water.

Pros:

• Exceptional Speed: Capable of outperforming nearly any monohull and most catamarans under 23 feet.
• Trailerability: The 8' 6" beam allows for standard road transport without the complexity of a tilting trailer.
• Ease of Handling: The self-tacking jib and boomless rig simplify maneuvers during high-speed racing.
• Build Quality: Aquarius Sail is known for robust, American-made construction that holds up better than many mass-produced beach cats.

Cons:

• Technical Rig: The high-aspect rig and rotating mast require a steeper learning curve for novice sailors.
• Niche Market: Finding replacement parts or specific sails may require going directly through the manufacturer rather than local lofts.
• Physical Demands: Despite its ease of handling, the boat generates significant power and requires an athletic crew to manage safely in heavy air.