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1979 Ryder Yachts Southern Cross 31

$22,500 USD

Seller's Description

Hull# 80

This boat is an excellent sailer and a lovely classic cruising sailboat.

trickle charge 20W solar panel and installed solar charge controller new stainless lifelines 2015 new saltwater washdown pump 2014 newly redone galley area w/ butcher block counter and stove cover/large cutting board, 7 deep stainless single sink, foot freshwater pump and bronze saltwater hand pump 2015 interior repainted/refinished entirely 2015 both diesel injectors rebuilt with new nozzles 2015 bowsprit replaced with custom bald cypress layup 2022, including all new stainless through-sprit hardware water damage in cabin sole repaired 2022 all through deck hardware from bow aft to cockpit rebedded 2022 hatch coaming rebuilt and rebedded 2022

She has been sitting on the hard for the last 5 years and we spent a month of big work days this summer.

She needs: 4 new house batteries new wood cheeks throughbolted on the upper rudder a new cabin sole covering of your choice. The subfloor has been repaired 2022, is all solid and painted dark brown. Add teak and holly plywood, faux teak and holly vinyl or your choice. diesel fuel cleaning/changing 80’ new 5/16”chain for primary anchor

She has been stored out of the water for the past 14 years whenever not in use.

Equipment: Engine: Yanmar 2QM15 15hp Diesel Racor fuel filter Fixed 3 blade prop

Electrical: Has 8 year old Trojan Deep cycle batteries in two banks, will need replacement.

Battery Charger, monitor Solar Charge Controller 20w trickle Solar Panel 110vac Shore power with 30amp connection and cord Galvanic isolator Pur Survivor 40 12v reverse osmosis water maker

Electronics are simple and period: Speed(needs new impeller), Depth, handheld Garmin GPS, VHF radio with additional external speaker, AM/FM/CD/aux input stereo, engine hour meter

Galley/Plumbing: Adler Barbour engine driven cold plate refrigeration, 3 burner propane stove w/oven, 2ea 10 gal aluminum propane tanks with regulator and solenoid, foot pump freshwater at galley and head, one 50 gallon freshwater tank, 3 large access ports, sewage holding tank, marine head replaced 2011, used little, large folding teak dining table, custom folding teak cockpit table.

Sails/Rigging: Primary sails are in excellent shape. Main w/ 2 reefs, 130% Genoa, Staysail, Storm sail and storm trysail. Yankee and Drifter in serviceable condition. New chainplates in 2006 along with rigging inspection. All new halyards and new delrin sheaves on boom 2015, all bronze winches two winch handles, flag halyard, halyard for radar reflector

Safety: New stainless lifelines (2015), one electric and two manual bilge pumps, three fire extinguishers, flare kit, horseshoe buoy, two offshore harnesses, jacklines, radar reflector, masthead and backup 12v anchor light

Anchoring: Manual 2 speed bronze windlass, dual bow rollers with 35# CQR with 200’ rode. 22# Danforth w/40’ chain and 200’ rode, 12’ Danforth with 20’ chain and 100’ rode, five bronze oversize deck cleats with bronze line chocks.

Misc: Eight bronze opening ports (all with screens), two opening lexan deck hatches, two solar vents, cockpit cushions, dodger and sunshade, outboard motor mount, propane Magma BBQ, compass (out for repair 2022), tiller extension, detachable folding teak swim ladder, bosun’s chair, wind scoop, misc spare parts for engine etc.



Thomas Gillmer
C. E. Ryder
# Built
Transom hung


Length Overall
31 0 / 9.5 m
Waterline Length
25 0 / 7.6 m
9 6 / 2.9 m
4 5 / 1.4 m
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



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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