The Southern Cross 31 Sailboat

The Southern Cross 31 is a classic cutter-rigged sailboat that was designed by Thomas Gillmer and built by C. E. Ryder between 1975 and 1987.

It is a sturdy and seaworthy vessel that draws inspiration from the traditional double-enders of Colin Archer, a Norwegian naval architect and shipbuilder. The boat has a full keel, a transom-hung rudder, and a small cockpit that offers protection in rough seas. It has a spacious interior with two layout options, one with a stand-up navigation station and one with a quarter-berth. The Southern Cross 31 is a popular choice for bluewater cruisers who value comfort, safety, and simplicity over speed and performance.

A Southern Cross 31 sailboatThe Southern Cross 31 long-keeled cutter

Published Specification for the Southern Cross 31

Underwater Profile: Long keel with transom-hung rudder

Hull Material: GRP

Length Overall: 31'0" / 9.5m

Waterline Length: 25'0" / 7.6m

Beam: 9'6" / 2.9m

Draft: 4'6" / 1.4m

Rig Type: Cutter

Displacement: 13,600lb / 6,169kg

Designer: Thomas Gilmer

Builder: Clark Ryder (USA)

Year First Built: 1975

Owners Association: Southern Cross Owners Association

Published Design Ratios for the Southern Cross 31

1. Sail Area/Displacement Ratio: 12.6

2. Ballast/Displacement Ratio: 32.4

3. Displacement/Length Ratio: 389

4. Comfort Ratio: 37.6

5. Capsize Screening Formula: 1.6

read more about these all-revealing numbers...

Summary Analysis of the Design Ratios for the Southern Cross 31

1. A Sail Area/Displacement Ratio of just 12.6 suggests that the Southern Cross 31 will need a stiff breeze to get her going. In light conditions, unless you've got plenty of time on your hands, motor-sailing may be the way to go.

2. A Ballast/Displacement Ratio of 32.4 means that unless the bulk of the ballast is concentrated in a bulb at the foot of her keel, the Southern Cross 31 will have a tendency to heel excessively in a gust, and she'll need to be reefed early to keep her sailing upright in a moderate breeze. 

3. A Displacement/Length Ratio of 389, tells us the Southern Cross 31 is firmly in the ultra-heavy displacement category. Load her up as much as you like and her performance will be hardly affected, not that it was ever startling. Few if any sailboats are built to this displacement category these days - but they remain popular with some long-distance sailors.

4. Ted Brewer's Comfort Ratio of 37.6 suggests that crew comfort of a Southern Cross 31 in a seaway is similar to what you would associate with the motion of a moderate bluewater cruising boat - a predictable and acceptable motion for most seasoned sailors.

5. The Capsize Screening Formula (CSF) of 1.6 tells us that a Southern Cross 31 would be a safer choice of sailboat for an ocean passage than one with a CSF of more than 2.0. 

Any Questions?

Is the Southern Cross 31 still in production and, if not, when did production end and how many of these sailboats were built?

No, the Southern Cross 31 is not in production anymore. The production ended in 1987, after 150 boats were built.

What is the history of the builders of the Southern Cross 31 and is the company still in business?

The Southern Cross 31 was built by C. E. Ryder, a company founded by Clint Ryder in 1968 in Bristol, Rhode Island. The company specialized in building high-quality fiberglass sailboats, such as the Sea Sprite, the Bristol Channel Cutter, and the Southern Cross series. The company ceased operations in 1990 and was sold to Bristol Yachts.

What sailplan and rig options, if any, are available for the Southern Cross 31?

The Southern Cross 31 has a cutter rig with a bowsprit, which allows for a variety of sail combinations depending on the wind conditions. The reported sail area is 46.1 m² (497 sq ft), which includes a mainsail, a staysail, and a yankee jib.

What keel options, if any, are available for the Southern Cross 31?

The Southern Cross 31 has only one keel option, which is a long keel with a cutaway forefoot. The keel has a draft of 1.4 m (4.6 ft) and a ballast of 1,995 kg (4,400 lbs), which gives the boat a ballast-to-displacement ratio of 32.3%. The long keel provides directional stability and protects the propeller and rudder from grounding.

What is the Southern Cross 31 like to sail?

The Southern Cross 31 is a heavy displacement boat that sails well in moderate to strong winds, but struggles in light airs. It is not very fast or agile, but it is stable and comfortable in rough seas. It has a well-balanced helm and responds well to the tiller. It can handle most weather conditions and has a reputation for being seaworthy and reliable.

What is the average cost of a secondhand Southern Cross 31?

The average cost of a secondhand Southern Cross 31 varies depending on the condition, equipment, and location of the boat. According to, the asking prices for Southern Cross 31 boats for sale range from US$10,900 to US$59,000 as of April 2023.

What other sailboats have been created by the designer of the Southern Cross 31?

Thomas Gillmer was a professor of naval architecture at the US Naval Academy and an accomplished designer of sailboats. Some of his other designs include the Allied Seawind, the Aries 32, the Blue Moon, the Offshore 33, and the Pride of Baltimore.

The above answers were drafted by using GPT-4 (OpenAI’s large-scale language-generation model) as a research assistant to develop source material; to the best of our knowledge, we believe them to be accurate.

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