The Westerly Berwick Sailboat
Specs & Key Performance Indicators

The Westerly Berwick, a masthead sloop, was designed by Laurent Giles and built in the UK by Westerly Marine Ltd.

A Westerly Berwick 31 sailboat on a mooringA Westerly Berwick 31

Published Specification for the Westerly Berwick

Underwater Profile: Bilge keels & semi-balanced rudder

Hull Material: GRP (Fibreglass)

Length Overall: 31'0" (9.5m)

Waterline Length: 25'0" (7.6m)

Beam: 9'6" (2.9m)

Draft: 3'7" (1.1m)

Rig Type: Masthead sloop

Displacement: 9,790lb (4,441kg)

Ballast: 4,436lb (2,012kg)

Designer: Laurent Giles

Builder: Westerly Marine Ltd (UK)

Year First Built: 1973

Year Last Built: 1980

Number Built: 309


Published Design Ratios for the Westerly Berwick

1. Sail Area/Displacement Ratio: 14.9

  • 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: 45.3

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

3. Displacement/Length Ratio: 280

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

4. Comfort Ratio: 28.1

  • 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: 1.8

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

Read more about these Key Performance Indicators...


Summary Analysis of the Design Ratios for the Westerly Berwick

1. A Sail Area/Displacement Ratio of just 14.9 suggests that the Westerly Berwick 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 45.3 means that the Westerly Berwick will stand up well to her canvas in a blow, helping her to power through the waves.

3. A Displacement/Length Ratio of 280, tells us the Westerly Berwick 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 28.1 suggests that crew comfort of a Westerly Berwick in a seaway is similar to what you would associate with the motion of a coastal cruiser with moderate stability, which is not the best of news for anyone prone to seasickness. 

5. The Capsize Screening Formula (CSF) of 1.8 indicates that a Westerly Berwick would be a safer choice of sailboat for an ocean passage than one with a CSF of more than 2.0. 

Other sailboats in the Westerly range include:


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