King Shark 20 Information, Review, Specs

The boat was born from the same design lineage as the "Wildcat" and other early MacAlpine-Downie successes. While modern beach cats have since surpassed it in raw speed, the Shark 20 remains a respected classic for its unique blend of stability, relatively high displacement-to-length efficiency, and its role in establishing the catamaran as a viable racing class. The King Marine versions are characterized by their vintage fiberglass layups and wood-accented crossbeams, which were robust for their era but require diligent maintenance today.

Sailing Performance & Handling

Sailing the Shark 20 is an exercise in 1960s-era "power sailing." With a massive 10-foot beam—exceptionally wide for a 20-foot boat—the Shark offers a stable platform that resists heeling far better than the narrow-beam monohulls of its day. This width allows the boat to carry a generous sail plan of approximately 285 square feet, resulting in a high Sail Area to Displacement (SA/Disp) ratio that ensures lively performance even in light air.

In terms of sea-kindliness, the Shark 20 is known for its ability to "plane" on its hulls rather than just cutting through the water. However, unlike modern piercing-bow catamarans, the Shark has relatively full bows that can be prone to "hobby-horsing" in a short chop. Handling is described by owners as technical but rewarding; the boat tracks well due to its deep symmetrical hulls and kick-up rudders, though it requires active weight management to prevent the leeward hull from digging in too deep during high-speed reaches. Because of its weight (roughly 650–800 lbs depending on the builder), it does not have the "flickable" feel of a Hobie 16, but it offers a much more composed and "big boat" feel on open water.

Popular Mentions & Media

The Shark 20 holds a distinguished place in the history of the Little Americas Cup, a competition that Rod MacAlpine-Downie dominated with his various designs. While the Shark 20 itself was more of a "people’s racer" than a one-off C-Class catamaran, it benefited immensely from the prestige of the MacAlpine-Downie name. The model is frequently cited in historical retrospectives of multihull development as the design that proved catamarans could be practical for the average sailor who needed to trailer their boat between lakes and coastal venues.

Known Issues & Buyer’s Checklist

Prospective buyers of a vintage Shark 20, particularly those built by King Marine or Gibbs, should focus on the following technical areas:

• Folding Mechanism Integrity: The most critical inspection point is the hinge system and the locking bolts that secure the hulls to the crossbeams. Over decades of use, the bolt holes can become "egged out," leading to structural play between the hulls while underway.
• Mast Step Compression: The downward force of the rig on the main crossbeam is significant. Check for hairline cracks in the fiberglass or rot in the wooden compression posts (if applicable) beneath the mast step.
• Hull Delamination: Early fiberglass production often involved balsa or plywood cores in the decks and transoms. Use a phenolic hammer to tap for "dead" thuds that indicate core rot or delamination, especially around the chainplates and hiking strap anchors.
• Rudder Assembly: The kick-up rudder housings on these boats are often cast aluminum or heavy-gauge stainless steel. Inspect the pivot pins and the "down-haul" locking mechanism, as these parts are difficult to replace and often require custom fabrication.

Community & Resources

The Shark 20 community is primarily found within broader vintage multihull groups. Technical data and historical discussions are often hosted by the International Shark Catamaran Association, which has historically managed the class rules and race results. While the association's digital presence has fluctuated, they remain the primary authority on the original MacAlpine-Downie specifications.

The Verdict

The Shark 20 is a vintage speedster that offers a unique bridge between the world of beach catamarans and larger coastal cruisers. It is an ideal choice for the sailor who appreciates nautical history and wants a stable, wide-platform catamaran that can still be stored in a standard driveway.

Pros:

• Remarkable stability due to the 10-foot beam.
• Trailerable design via the innovative folding hull system.
• High-performance pedigree with a generous sail-to-weight ratio.
• Large trampoline area provides more "deck" space than many 25-foot monohulls.

Cons:

• Significant maintenance requirements for the folding hinges and older fiberglass.
• Heavy compared to modern 20-foot catamarans, making beach launching difficult.
• Fuller hull shapes can lead to spray and "pitch-poling" risks if pushed too hard in heavy seas.