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1980 Southern Cross 31

Glen Burnie, Maryland, United States
$35,000 USD

3- blade prop in aperture

Sails: mainsail, roller furled genoa, hank-on staysail

Anchors – Spade & 2 Bruce or Claw Type

Electronics – Functioning – VHF, Radar, Depth, GPS, Compass, Battery Charger (Charges All common Types)

Electronics – Need wiring completed to Assess– SSB Tuner & Pactor Modem (Untested, Not Connected to Antenna), Wind Speed at Masthead {Need Wired from Below-Deck and May Need Display} and for newer Speed/Temp thru-Hull instruments (has Display)

Features – Original Ideal Windlass (Untested Rode only – Schaefer Marine Can Upgrade to Chain/Refurbish)

Monitor WindVane – Excellent Condition, Multiple vanes

Propane Heater Force 10 Fwd Salon Stb Bulkhead Mounted - Untested

Force 10 Propane Stove 3-Burner– Lights with hand igniter or match, needs auto- igniters/batteries replaced, Oven/Broiler Untested.

Propane 2 Tanks Aluminum 11 lb. Auto Shut-off Solenoid. Tank Box On-Deck Behind Mast

Repairs – Galley Thru-hulls Replaced ‘21, Rubrails Repaired ‘21

Tiller – Steering

Custom -Factory built double fwd berth - Stowage Beneath

Dodger – Stainless Frame

Mainsail Traveler - Original, Lazy Jacks

100’ Chain on each bow anchor, several 100’ stern anchor web on roller

Tankage – 70 Gallons Fresh Water Tank Below Sole, 37 Gallons Diesel Tank Below Sole, 20 Gallon Waste below Fwd Berth

Head Stb– Single Sink Bowl with Operating Hand Pump – refurbished seals etc. Lavac Vacuum Toilet, Refurbished, Operating, Shower – None Installed

Port Galley – 2 -Sink, Fresh Water Foot Pump, 12V Saltwater Pump, 3 Burner Stove, 2-Lid Ice Box, Thick Wooden Cutting Board, Enclosed dish & pot storage outboard, all portside. Above sink are open compartments storage.

Companion – Hanging Steps, Drop Boards to Access Yanmar Engine and Thru -Hulls, Bilge Pump And Access. Aft of Steps is Main Electrical Panel. Propane Solenoid Above Ice Box

Stbd Chart - Table Lift Top With Instruments Mentioned above & outboard. Radar on Swivel. Battery Charger Aft in Own locker

Salon – 2 Single berths With Lee-Cloths. Swivel Table [Removable To cockpit]. Carpet on Sole

Stowage – In Salon above and below Settees & fwd under berth and in lockers, cubbies

Portlights- 8 -Round Bronze Opening with hangers. Homemade screening being tested.

Hatches - 2 Bomar opening. Home-made screening

On Deck - Main Sheet Traveler – Appears original, functional. Raft Holding Frame, Deck Mounted Mast, Beefy Standing Rigging, Belaying Pin Racks, Removable Staysail Stay, Mast-steps to top. Solid SS rear frame connecting back-Stay, Rear Anchor Platform, Boarding Ladder.

Price is As-Found. USCG Documented.

Health Issues determined after Purchase Prevent Continuing Original Plans.

This listing is presented by SailFarYachts.com. Visit their website for more information or to contact the seller.

View on SailFarYachts.com


Thomas Gillmer
C. E. Ryder
# Built
Transom hung


Length Overall
31 0 / 9.5 m
Waterline Length
13,600 lb / 6,169 kg
4,400 lb / 1,995 kg

Rig and Sails

Reported Sail Area
496′² / 46.1 m²
Total Sail Area
495′² / 46 m²
Sail Area
213′² / 19.8 m²
31 5 / 9.6 m
13 5 / 4.1 m
Air Draft
Sail Area
283′² / 26.3 m²
36 6 / 11.1 m
15 5 / 4.7 m
Forestay Length
39 7 / 12.1 m

Auxilary Power

Fuel Type
Fuel Capacity
Engine Hours


Water Capacity
Holding Tank Capacity


Hull Speed
6.5 kn
Classic: 6.7 kn

Hull Speed

The theoretical maximum speed that a displacement hull can move efficiently through the water is determined by it's waterline length and displacement. It may be unable to reach this speed if the boat is underpowered or heavily loaded, though it may exceed this speed given enough power. Read more.


Classic hull speed formula:

Hull Speed = 1.34 x √LWL

A more accurate formula devised by Dave Gerr in The Propeller Handbook replaces the Speed/Length ratio constant of 1.34 with a calculation based on the Displacement/Length ratio.

Max Speed/Length ratio = 8.26 ÷ Displacement/Length ratio.311
Hull Speed = Max Speed/Length ratio x √LWL

6.47 knots
Classic formula: 6.7 knots
Sail Area/Displacement
<16: under powered

Sail Area / Displacement Ratio

A measure of the power of the sails relative to the weight of the boat. The higher the number, the higher the performance, but the harder the boat will be to handle. This ratio is a "non-dimensional" value that facilitates comparisons between boats of different types and sizes. Read more.


SA/D = SA ÷ (D ÷ 64)2/3

  • SA: Sail area in square feet, derived by adding the mainsail area to 100% of the foretriangle area (the lateral area above the deck between the mast and the forestay).
  • D: Displacement in pounds.
<16: under powered
16-20: good performance
>20: high performance
<40: less stiff, less powerful

Ballast / Displacement Ratio

A measure of the stability of a boat's hull that suggests how well a monohull will stand up to its sails. The ballast displacement ratio indicates how much of the weight of a boat is placed for maximum stability against capsizing and is an indicator of stiffness and resistance to capsize.


Ballast / Displacement * 100

<40: less stiff, less powerful
>40: stiffer, more powerful
>350: ultraheavy

Displacement / Length Ratio

A measure of the weight of the boat relative to it's length at the waterline. The higher a boat’s D/L ratio, the more easily it will carry a load and the more comfortable its motion will be. The lower a boat's ratio is, the less power it takes to drive the boat to its nominal hull speed or beyond. Read more.


D/L = (D ÷ 2240) ÷ (0.01 x LWL)³

  • D: Displacement of the boat in pounds.
  • LWL: Waterline length in feet
<100: ultralight
100-200: light
200-300: moderate
300-400: heavy
>400: very heavy
Comfort Ratio
30-40: moderate bluewater cruising boat

Comfort Ratio

This ratio assess how quickly and abruptly a boat’s hull reacts to waves in a significant seaway, these being the elements of a boat’s motion most likely to cause seasickness. Read more.


Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam1.33)

  • D: Displacement of the boat in pounds
  • LWL: Waterline length in feet
  • LOA: Length overall in feet
  • Beam: Width of boat at the widest point in feet
<20: lightweight racing boat
20-30: coastal cruiser
30-40: moderate bluewater cruising boat
40-50: heavy bluewater boat
>50: extremely heavy bluewater boat
Capsize Screening
<2.0: better suited for ocean passages

Capsize Screening Formula

This formula attempts to indicate whether a given boat might be too wide and light to readily right itself after being overturned in extreme conditions. Read more.


CSV = Beam ÷ ³√(D / 64)

  • Beam: Width of boat at the widest point in feet
  • D: Displacement of the boat in pounds
<2: better suited for ocean passages
>2: better suited for coastal cruising


From BlueWaterBoats.org:

The Southern Cross 31 is a no nonsense double-ender designed by Tom Gillmer, a professor of naval architecture at the US Naval Academy. The design takes influence from shapes dating back to Colin Archer’s work nearly a century earlier, and the hull in many respects is similar the straight transomed Allied Seawind 30, an earlier Gillmer creation notable for being the first fiberglass boat to circumnavigate the globe. (The Allied Seawind 30 was successful enough to be updated to the Allied Seawind II)

She’s a full keeled sailboat with an outboard rudder and tiller combo, a configuration often praised for its simplicity and the cockpit is quite small, suitable for ocean passages. The cutter rig with bowsprit has 447 sq. ft. of canvas, plenty for its displacement, but being a heavy displacement boat performance is hampered in light airs. Looking on the bright side, the weight gains dividends with a comfortable motion while underway.

Two interior layouts were offered, one with a stand up navigation station over a large locker and one with quarter-berth. The overall construction quality was of a good standard, suitably strong for offshore work. The hulls were built in fiberglass with the topsides cored in Airex foam, while the deck and cabin house was cored in balsa.

In total 130 boats were built between 1976 and 1987, of which a number were sold as hull and deck kits. A slightly larger and similar Gillmer design is the Aries 32 (around 20 of these were built).

Links, References and Further Reading

» Southern Cross Owners Association
» Twenty Small Sailboats to Take You Anywhere by John Vigor, (Ch19, p117-123) an in depth look at the Southern Cross 31. ISBN:978-0939837328
» Ryder Yachts



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