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Sailboat Specifications

Thai Mk Iv

Frac. Sloop (Rotating Spar) · Catamaran Twin Cbrd.

Designed by J.r. (Rod) Macalpine-Downie · Built by Sailcraft (Uk) · First built 1958

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LOA 17.00 ft  ·  Beam 6.00 ft  ·  Displacement 250.00 lb  ·  Sail Area 220.00 ft²  ·  Frac. Sloop (Rotating Spar)  ·  Catamaran Twin Cbrd.
About the Thai Mk Iv Sailboat

Designed by J.R. (Rod) Macalpine-Downie and first launched in 1958, this compact catamaran represents an early exploration into multihull sailing for the recreational market. Built by Sailcraft in the UK, the Thai Mk IV features traditional wood construction combined with innovative twin centerboard configuration that allows for shallow water exploration and easy beaching. At just 17 feet overall with a 6-foot beam and remarkably light 250-pound displacement, this fractional sloop-rigged catamaran delivers impressive performance through its generous 220 square feet of sail area. The rotating spar setup enhances sail efficiency and reduces weight aloft, contributing to the boat's lively sailing characteristics. With a SA/Displacement ratio of 88.78, expect spirited performance in light to moderate conditions. The shallow 2-foot draft opens up cruising grounds typically inaccessible to deeper-keeled boats, making this an excellent choice for exploring shallow bays, rivers, and coastal areas. Its lightweight construction and twin hulls provide inherent stability and quick acceleration, though the narrow beam requires active sailing techniques typical of performance catamarans. Best suited for day sailing, short coastal hops, and sailors seeking an engaging, responsive boat that rewards skill and attention at the helm.

Dimensions & Specifications
LOA (Length Overall) 17.00 ft / 5.18 m
Beam 6.00 ft / 1.83 m
Max Draft 2.00 ft / 0.61 m
Min Draft 0.50 ft / 0.15 m
Displacement 250.00 lb / 113 kg
Sail Area (Reported) 220.00 ft² / 20.44 m²
Design & Construction
Hull Type Catamaran Twin Cbrd.
Rigging Type Frac. Sloop (Rotating Spar)
Construction Wood
Designer J.R. (Rod) Macalpine-Downie
Builder Sailcraft (UK)
First Built 1958
Related Sailboats Hobie 17 · Tiger Cat · Nacra 52 · Thistle · Harpoon 52
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Frequently Asked Questions

What is the Thai Mk Iv's comfort ratio?

The Thai Mk Iv has a Ted Brewer Comfort Ratio of 2.32. A ratio over 30 indicates good offshore comfort; over 40 is very comfortable offshore.

Is the Thai Mk Iv safe for offshore sailing?

The Thai Mk Iv has a Capsize Screening Formula value of 3.81. Values under 2.0 are considered acceptable for offshore sailing; under 1.8 is ideal.

What is the hull speed of the Thai Mk Iv?

The theoretical hull speed of the Thai Mk Iv is 5.09 kn knots, calculated from its waterline length.

How much does a Thai Mk Iv weigh?

The Thai Mk Iv has a displacement of 250.00 lb and a length overall (LOA) of 17.00 ft.

Who designed the Thai Mk Iv?

The Thai Mk Iv was designed by J.r. (Rod) Macalpine-Downie, first built in 1958.