The Southerly 115 Sailboat

The Southerly 115 was designed by Dick Carter and built in the UK by Northshore Yachts Ltd.

A Southerly 115 Swing-Keel Cruiser

Shown above and described below is the single-rudder MkII version, unlike versions III and IV with twin rudders which enabled the boat to dry-out upright.

Published Specification for the Southerly 115

Underwater Profile: Swing keel

Hull Material: GRP (Fiberglass)

Length Overall: 36'10" (11.2m)

Waterline Length: 27'6" (8.40)

Beam: 11'11" (3.6m)

Draft: 2'3" (0.7m) with keel up; 8'1" (2.46 m) with keel down

Rig Type: Masthead sloop

Displacement: 15,215lb (6,902kg)

Designer: Dick Carter

Builder: Northshore Yachts (UK)

Year First Built: 1983

Owners Association: Southerly Owners Association

Published Design Ratios for the Southerly 115

1. Sail Area/Displacement Ratio: 10.0

Less than 16 would be considered under-powered;
16 to 20 would indicate reasonably good performance;
Over 20 suggests relatively high performance.

2. Ballast/Displacement Ratio: 49.9

Under 40: less stiff, less powerful
Over 40: stiffer, more powerful

3. Displacement/Length Ratio: 327

Under 100: Ultralight
100 to 200: Light
200 to 275: Moderate
275 to 350: Heavy
Over 350: Ultraheavy

4. Comfort Ratio: 28.6

Under 20 indicates a lightweight racing boat
20 to 30 indicates a coastal cruiser
30 to 40 indicates a moderate offshore cruising boat
40 to 50 indicates a heavy offshore boat
Over 50 indicates an extremely heavy offshore boat

5. Capsize Screening Formula: 1.9

Under 2.0 (the lower the better): Better suited for ocean passages
Over 2.0: Less suited for ocean passages

Summary Analysis of the Design Ratios for the Southerly 115

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1. A Sail Area/Displacement Ratio of just 10.0 suggests that the Southerly 115 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 49.9 means that the Southerly 115 will stand up well to her canvas in a blow, helping her to power through the waves.

3. A Displacement/Length Ratio of 327, tells us the Southerly 115 is clearly a heavy displacement cruising boat. You can load her down with all your cruising gear and equipment and it will hardly affect her waterline. Not an ideal choice for coastal sailing, but she'll come into her own on an offshore passage in testing conditions.

4. Ted Brewer's Comfort Ratio of 28.6 suggests that crew comfort of a Southerly 115 in a seaway is similar to what you would associate with the motion of a coastal cruiser with moderate stability, which is not encouraging news for anyone prone to seasickness.

5. The Capsize Screening Formula (CSF) of 1.9 tells us that a Southerly 115 would be a safer choice of sailboat for an ocean passage than one with a CSF of more than 2.0.