The Westerly Tempest 31 Sailboat
Specs & Key Performance Indicators

The Westerly Tempest 31, a masthead sloop, was designed by Ed Dubois and built in the UK by Westerly Marine Ltd.

Westerly Tempest 31

Published Specification for the Westerly Tempest 31

Underwater Profile: Fin Keel & Spade Rudder

Hull Material: GRP (Fibreglass)

Length Overall: 30'7" (9.3m)

Waterline Length: 24'6" (7.5m)

Beam: 10'10" (3.3m)

Draft: 5'0" (1.5m)

Rig Type: Masthead sloop

Displacement: 9,019lb (4,019kg)

Ballast: 2,690lb (1,220kg)

Designer: Ed Dubois

Builder: Westerly Marine Ltd (UK)

Year First Built: 1987

Year Last Built: 1993

Number Built: 107


Published Design Ratios for the Westerly Tempest 31

1. Sail Area/Displacement Ratio: 14.8

  • 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: 29.8

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

3. Displacement/Length Ratio: 274

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

4. Comfort Ratio: 22.2

  • 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: 2.1

  • 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 Tempest 31

1. A Sail Area/Displacement Ratio of just 14.8 suggests that the Westerly Tempest 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 29.8 means that a sailboat like the Westerly Tempest 31 (which doesn't have a stiffness-enhancing bulb keel), is likely to benefit from being reefed early to keep her sailing upright in a moderate breeze.

3. A Displacement/Length Ratio of 274, tells us the Westerly Tempest 31 is a moderate displacement cruiser, which means she'll carry all your cruising gear without it having a dramatic effect on her performance. Most of today's sailboats intended for offshore cruising fall into this displacement category.

4. Ted Brewer's Comfort Ratio of 22.2 suggests that crew comfort of a Westerly Tempest 31 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 of 2.1 tells us that a Westerly Tempest 31 would not be as good a choice of sailboat for ocean passage-making, owing to the increased risk of capsize in strong winds and heavy seas when compared to a sailboat with a CSF of less than 2.0.

Other sailboats in the Westerly range include:

Recent Articles

  1. Used Sailboats for Sale in the Caribbean

    Jun 07, 23 01:51 AM

    Looking for used sailboats for sale that are capable of crossing an ocean? These cruising yachts are already in the Caribbean, but what are the risks and benefits of buying out there?

    Read More

  2. 'Shindig', a 40ft Bluewater Cruising Yacht for Sale

    Jun 04, 23 08:32 AM

    If you're looking for a unique Bluewater Cruising Yacht for sale in the Caribbean, then 'Shindig' is certainly worth a look...

    Read More

  3. Used Sailing Equipment For Sale

    Jun 04, 23 06:26 AM

    Here's where people with sailing equipment for sale advertise their stuff entirely free of charge. If you're looking for used sailing gear or other used boating accessories, here's where to find it!

    Read More