The Westerly Tempest 31 Sailboat
Specs & Key Performance Indicators

The Westerly Tempest 31, a masthead sloop, is a sailboat designed by British naval architect Ed Dubois and constructed by Westerly Yachts, a UK-based boat-building company.

A Westerly Tempest 31, moored on the River Tamar in Southwest England

The Tempest 31 is part of Westerly's extensive line of family cruisers.The production of this model began in 1987 at Westerly Yachts' facilities located in Waterlooville, England. The design of the Tempest 31 reflects Dubois' emphasis on performance and comfort, making it a popular choice among cruising enthusiasts.

Westerly Tempest 31 Accommodation Layout

The Tempest had a surprising amount of space and comfort below decks, thanks to its clever layout and design. The boat could sleep up to six people in three separate cabins: two spacious double aft cabins under the cockpit, and one V-berth forward cabin with access to the sail locker.

Alternative versions of the Tempest became available during its production run. At the end of 1988, Westerly offered a choice of layouts, with an alternative design with a single larger aft cabin, aft heads, and conventional vee-berth forecabin. This option provided a much larger cockpit locker and was called the "Classic Option". However, most boats sold were the "Original" twin aft cabin version.

Just over 100 Tempests were built between 1987 and 1993, when the hull design, interior, and rig were reworked and renamed the Regatta 310. This model nominally remained in production until 1997, though in those six years only five were built.

Ed Dubois designed the Tempest as a smaller version of the racing-orientated Storm 33. Thanks to broader aft sections, it acted as a more cruising-friendly alternative to the existing 32 ft Fulmar design. The Tempest also had higher quality joinery than the earlier Fulmars, which were conceived as racing-capable boats. The Fulmar continued in production in parallel with the Tempest. The bilge keel option had twin well-angled and efficient keels with bulbs at the base to keep the center of gravity low, as well as slightly more keel weight than the fin keel versions.

Published Specification for the Westerly Tempest 31

Underwater Profile: Fin Keel (or a bilge keel option) & 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

The Westerly Tempest 31, with a Sail Area/Displacement Ratio of 14.8, suggests it's somewhat underpowered compared to high-performance boats but should still offer adequate sail power for recreational cruising.

Its Ballast/Displacement Ratio at 29.8 indicates moderate stability; this boat won't stand up to the wind as rigidly as boats with higher ratios, and the effectiveness of the ballast could be impacted by its distribution, as concentrated lower ballast typically offers enhanced stiffness.

The Displacement/Length Ratio of 274 places the Westerly Tempest 31 firmly within the moderate displacement category, suggesting that while it may not be the quickest in its class, it provides a balance between responsive handling and the substantive feel preferred in family cruising yachts.

Its Comfort Ratio, at 22.2, falls into the range associated with coastal cruisers, which implies that it should provide a reasonable degree of motion comfort in typical sailing conditions, although it may not handle very rough seas as comfortably as heavier displacement boats.

The Capsize Screening Formula score of 2.1 rounds off its profile as mostly suitable for coastal cruising, indicating a lower risk of capsize in rough weather than lighter or beamier boats, but still below the optimum for rigorous ocean passages.

It's crucial to recognize the theoretical nature of these ratios: they provide a framework for understanding a boat's characteristics but do not encompass every variable such as actual loading conditions, sea state, and seamanship skills. The Ballast/Displacement Ratio, for example, does not account for ballast location, only its proportion. Similarly, Ted Brewer's Comfort Ratio has its limitations, particularly in scoring modern light-displacement, beamy cruisers, which may offer a different kind of bluewater capability than the traditionally favored heavy, narrow designs.

Read more about Design Ratios...

Other Designs by Ed Dubois

Ed Dubois was a prolific yacht designer who created a wide range of boats. Here are some of his notable designs:

Borsalino Trois: This was his first solo commission, a larger Three Quarter Tonner designed in 1976.

Police Car: A 42ft Two Tonner that helped the Australian team to victory in the 1979 Admiral’s Cup.

Victory: Peter de Savary’s 12 Metre yacht, built as the British contender for the 1983 America’s Cup.

Enigma: One of his 1978 Quarter Ton designs.

Westerly Griffon: A successor to the 26ft Westerly Centaur, which remains the most numerous British built yacht.

Westerly Fulmar: Cited by many as being the once dominant British boat builder’s best ever model.

Centurions: Ranging from 36ft-59ft.

Southerly 535 and 57RS: Attractive upmarket Southerly cruisers.

Oyster 100 and 125: The largest Oyster models ever built.

Superyachts: Including Kokomo, Timoneer II, Silvertip, Tiara, Zulu II and Mondango II.

This is not an exhaustive list and Ed Dubois designed many other boats during his career. His designs ranged from modest production cruisers to world-beating racers and stunning superyachts

The above text was drafted by sailboat-cruising.com using GPT-4 (OpenAI’s large-scale language-generation model) as a research assistant to develop source material; we believe it to be accurate to the best of our knowledge.