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Sailboat Specifications

Monsun 31

Masthead Sloop · Long Keel

Designed by Olle Enderlein · Built by Hallberg-Rassy · First built 1974

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LOA 30.75 ft  ·  Beam 9.42 ft  ·  Displacement 9,250.00 lb  ·  Sail Area 414.00 ft²  ·  Masthead Sloop  ·  Long Keel
About the Monsun 31 Sailboat

Swedish builder Hallberg-Rassy produced 904 examples of this capable coastal cruiser between 1974 and 1982, establishing the Monsun 31 as one of their most successful early designs. Designer Olle Enderlein created a traditional yacht that exemplifies Scandinavian seaworthiness, featuring a long keel configuration that provides excellent directional stability and predictable handling characteristics. With a displacement of 9,250 pounds and substantial ballast of 4,200 pounds, this fiberglass sloop offers the kind of steady, comfortable motion that makes extended passages enjoyable. The masthead rig carries 414 square feet of sail area, providing adequate power while remaining manageable for a small crew. Her beam of 9.42 feet creates reasonable interior volume within the compact 30.75-foot length overall. The Monsun 31's impressive comfort ratio of 27.2 reflects her ability to handle rough conditions with minimal motion, while the conservative capsize screening value of 1.8 indicates good stability reserves for offshore work. This combination makes her well-suited for serious coastal cruising and short offshore passages, particularly in the challenging conditions common to Northern European waters where Hallberg-Rassy built their reputation for solid, seaworthy yachts.

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The balsa-cored deck used on the Monsun 31 is prone to moisture ingress around chainplates, stanchion bases, and deck hardware. Soft spots are common and should be probed carefully during survey, particularly amidships and around the cockpit coamings.
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The long keel is cast iron and the keel-to-hull joint on older examples is prone to rust weeping and sealant failure. The joint should be inspected carefully for rust staining and the sealant bedding compound checked for integrity, as water intrusion can cause internal hull laminate damage.
1974–1979 models
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The chainplate backing plates are glassed into the hull liner and are difficult to inspect without removing interior joinery. Corrosion and loosening of these backing plates is a known issue and has led to chainplate failures on aging examples.
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Dimensions & Specifications
LOA (Length Overall) 30.75 ft / 9.37 m
LWL (Waterline Length) 24.67 ft / 7.52 m
Beam 9.42 ft / 2.87 m
Max Draft 4.58 ft / 1.40 m
Displacement 9,250.00 lb / 4,196 kg
Ballast 4,200.00 lb / 1,905 kg
Sail Area (Reported) 414.00 ft² / 38.46 m²
Design & Construction
Hull Type Long Keel
Rigging Type Masthead Sloop
Construction FG
Designer Olle Enderlein
Builder Hallberg-Rassy
First Built 1974
Last Built 1982
Number Built 904
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Engine & Accommodations
Engine Make Volvo Penta
Engine Model MD 11 C
Engine Type Diesel
Fuel Capacity 32 gals / 121 L
Water Capacity 43 gals / 163 L
Frequently Asked Questions

What is the Monsun 31's sail area to displacement ratio?

The Monsun 31 has a Sail Area to Displacement ratio (SA/D) of 15.08. Values between 14–18 are typical cruising sailboats; 18–22 is cruiser/racer; over 22 is performance racing.

What is the Monsun 31's comfort ratio?

The Monsun 31 has a Ted Brewer Comfort Ratio of 27.2. A ratio over 30 indicates good offshore comfort; over 40 is very comfortable offshore.

Is the Monsun 31 safe for offshore sailing?

The Monsun 31 has a Capsize Screening Formula value of 1.8. Values under 2.0 are considered acceptable for offshore sailing; under 1.8 is ideal.

What is the hull speed of the Monsun 31?

The theoretical hull speed of the Monsun 31 is 6.66 kn knots, calculated from its waterline length.

How much does a Monsun 31 weigh?

The Monsun 31 has a displacement of 9,250.00 lb and a length overall (LOA) of 30.75 ft.

Who designed the Monsun 31?

The Monsun 31 was designed by Olle Enderlein, first built in 1974.