What truly set the Shark apart from its contemporaries was its refined hull shape and solid ergonomics. The hulls are symmetrical, featuring a relatively narrow waterline beam and a clean, straight profile with minimal rocker. This design minimizes wave-making resistance, allowing the Shark to easily outpace the popular beach cats of the subsequent decade, such as the Hobie 16, which relied on banana-shaped asymmetrical hulls that generated significant drag. Rather than sitting on a narrow, wet trampoline, the crew enjoys a flat cockpit layout stretching from gunwale to gunwale. This design consists of a central trampoline bounded by solid hull decks and robust structural crossbeams. Under these wide, flat hull decks, the Shark features a surprising amount of dry storage space accessed via deck hatches. This practical interior volume makes the boat an iconic choice for long-distance beach camping and coastal exploration.
Design Brief & Intent
The design brief of the Shark Catamaran focused on maximizing aerodynamic and hydrodynamic efficiency within the B-Class racing catamaran limits of the era. Rod Macalpine-Downie and Dick Gibbs envisioned a boat that was not only fast on a racecourse but also safe and adaptable enough for coastal day-sailing. To achieve this, they incorporated twin pivoting centerboards housed in trunks within each hull. This configuration represents a major departure from other builders of the time, who often favored boardless hulls or fixed daggers that were highly vulnerable to damage in shallow water. The twin centerboards allow the Shark to point remarkably high and tack with the agility of a monohull, completely avoiding the sluggishness and slide common in early catamaran designs.
The interior of the hulls—though devoid of standing headroom or complex amenities—is beautifully finished with high-quality joinery that reflects the era’s craftsmanship 3. Early hulls were crafted from cold-molded wood or marine plywood, while later production shifted to fiberglass. Regardless of the construction material, the under-deck layout was optimized for gear storage, enabling sailors to pack tents, sleeping bags, and supplies securely away from the elements. This capability separated the Shark from pure beach toys, elevating it to a versatile, high-speed pocket passage-maker.
Variations & Configurations
The Shark Catamaran saw a few structural variations over its long production run, which was shared among Gibbs Boat Company, MFG (Molded Fiber Glass) Boat Company, and Sail Craft Ltd. in the United Kingdom. Early models built in LaSalle, Michigan by Gibbs Boat Company were cold-molded wood or premium Okoume marine plywood hulls paired with solid mahogany crossbeams 6. These wooden versions are highly prized for their lighter weight and classic aesthetics. Following MFG’s acquisition of Gibbs in 1972, production transitioned to more durable, low-maintenance fiberglass hulls. While the fiberglass hulls were tougher and more forgiving of neglect, they typically came in slightly heavier than the wooden versions, making the cold-molded models the preferred choice for dedicated racers.
The rig configuration remained largely standardized to preserve its competitive one-design status. It features a fractional sloop rig with a highly sophisticated rotating spar. The rotating mast is a critical component, as it allows the mast and the mainsail to align perfectly with the apparent wind, forming a continuous, highly efficient wing-like airfoil. Draft options are inherently variable due to the twin pivoting centerboards. With the boards raised, the boat draws a mere five inches, allowing it to glide over shoals and sail directly onto sandy beaches. With the boards fully lowered to two and a half feet, the boat gains maximum lateral resistance for outstanding upwind performance.
Sailing Performance & Handling
At the helm, the Shark Catamaran is an incredibly responsive and rewarding boat to sail. Boasting a featherweight displacement of just 300 pounds, it requires minimal wind to break away from its own drag. The boat’s sail-area-to-displacement ratio of 83.9 is nothing short of astronomical. This mathematical reality translates into explosive acceleration and the ability to generate its own apparent wind, easily sailing at speeds that exceed the true wind velocity in light-to-moderate air. It climbs up to its top speeds effortlessly, and in a strong breeze, it is capable of sustained double-digit speeds in the high teens and low twenties.
This extreme performance potential is further highlighted by its displacement-to-length ratio of 27.26, which firmly establishes the Shark as an ultra-light racer. The narrow hulls slice cleanly through chop with minimal wave-making resistance, reducing the violent pitching motions often associated with wider-hulled multihulls of the same length.
The capsize screening ratio of 5.98 and comfort ratio of 1.21 must be interpreted within the context of a high-performance multihull. On a monohull, these ratios would indicate a tender and highly active motion; on the Shark, they accurately reflect a lively, highly communicative platform. The boat demands active crew participation, including hiking and the use of the trapeze to balance the massive sail plan. When properly sailed, the combination of the rotating spar and pivoting centerboards keeps the boat tracking like a freight train, offering a stiff, locked-in feel that rewards precise sail trim and helm adjustments 1.
Known Issues & Triage
For those looking to purchase or restore a vintage Shark Catamaran, there are several critical structural areas that require close inspection. The most prevalent issue is rot in the wooden components, particularly on early cold-molded models or fiberglass models utilizing plywood-cored decks. Plywood decks can delaminate and turn soft, especially around the chainplates, hatches, and the joints where the deck meets the hull. Triage requires cutting away the damaged skin, replacing the rotted wood with fresh marine-grade plywood, and sealing the entire assembly with epoxy and fiberglass cloth.
Another critical high-stress point is the folding mechanism itself. The 7/8-inch thick mahogany crossbeams are cut in the center and joined by heavy stainless steel hinges to allow the hulls to fold together for transport. These beams are subjected to immense torsional and bending loads while sailing. Over time, water can penetrate the bolt holes holding the hinges, leading to rot and structural softening within the wood. If these connection points are compromised, the crossbeams can split or the hinges can pull free under sail, leading to catastrophic hull separation. Owners must regularly inspect the integrity of the mahogany around these hinges and rebuild any soft sections with epoxy and high-density fillers.
Finally, the centerboard trunks and rudder gudgeons are prone to stress wear. The leverage exerted by the high-aspect centerboards can create spiderweb stress cracks at the base of the trunks where they interface with the hull. Similarly, the original rudder castings and rudders can suffer from fatigue and play, requiring shimming or structural reinforcement to prevent binding or failure at high speeds.
Modernization & Upgrades
Modern owners committed to keeping these vintage classics on the water are utilizing contemporary materials to resolve historical weaknesses. One of the most significant upgrades is the conversion of the crossbeams from traditional solid mahogany to composite foam-core and carbon-fiber assemblies. By laminating a foam core wrapped in multiple layers of carbon-fiber and epoxy, owners can create a stiffer, stronger crossbeam that completely eliminates the risk of rot while shaving significant weight from the boat. This modification drastically improves the stiffness of the platform, ensuring more direct energy transfer from the sails to the hulls.
Sail plans are also commonly updated. Replacing tired Dacron sails with modern aramid laminates and utilizing a square-top, full-batten mainsail design allows the Shark to extract even more performance from its rotating spar. Additionally, many owners choose to reshape the original flat plate rudders. By rebuilding the rudders with a modern NACA airfoil profile, drag is significantly reduced, helm touch is lightened, and cavitation at high speeds is virtually eliminated.
The Verdict
The Shark Catamaran is a masterpiece of early multihull engineering that successfully married explosive performance with practical trailering. While it requires more structural vigilance and maintenance than modern mass-produced plastic beach cats, its combination of speed, pointing ability, and generous on-deck space makes it an outstanding choice for classic multihull enthusiasts and adventurous beach-camping sailors 3.
Pros
- Astounding speed and explosive acceleration, especially in light-to-moderate wind
- Innovative folding design allows for easy trailering and storage without disassembling the trampoline
- Symmetrical hull design and pivoting centerboards deliver superior pointing ability and easier tacking
- Flat deck layout and generous hull volume offer ample storage for long-distance beach camping
- Highly efficient rotating spar rig maximizes sail performance and aerodynamic efficiency
Cons
- Original wooden hulls, plywood decks, and stringers are highly susceptible to rot if neglected
- Extreme torsional stress on the folding hinge mechanism requires frequent structural safety inspections
- High-tension rig can cause compression fatigue on the mast step and main crossbeam
- Lightweight, high-powered setup requires active crew handling and can be unforgiving in heavy air
