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 (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

1. Sail Area/Displacement Ratio: 14.8

2. Ballast/Displacement Ratio: 29.8

3. Displacement/Length Ratio: 274

4. Comfort Ratio: 22.2

5. Capsize Screening Formula: 2.1

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.

More about the Westerly Tempest 31...

The Westerly Tempest 31 is built to high standards of quality and durability, with a double gelcoat to both external and internal surfaces, temperature and humidity-controlled laminating, fire retardant foam in all upholstery, solid teak toe rails, grab handles and rubbing strake, 316 high grade stainless steel fittings, and keel studs 50% over Lloyds specification with locking bolts. The boat also has a Lloyds Hull Construction Certificate, which attests to its structural integrity.

Westerly Tempest 31 Accommodation LayoutWesterly Tempest 31 Accommodation Layout

The Westerly Tempest 31 has a surprising amount of space and comfort below decks, thanks to its clever layout and design. The boat can 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. All cabins have opening ports or hatches for ventilation and light, as well as storage lockers or shelves for personal belongings.

The saloon is bright and airy, with a folding table on the centerline that can seat six people comfortably on the fabric-covered sofas. Behind the seats are teak lockers that provide ample storage space for books, games, or other items. There is also more storage space under the seats and under the cabin sole.

The galley is located to starboard of the companionway, and is well-equipped with a gimballed two-burner cooker with oven, grill and crash bar, a drained insulated icebox, a stainless steel sink with pressurized water system, teak fiddles around the worktop, and plenty of cupboards and drawers for crockery, cutlery, pots and pans.

The navigation area is located to port of the companionway, and has a pull-out swivel seat that can be stowed away when not in use. The chart table has enough space for charts and instruments, as well as a panel for electrical switches and circuit breakers. There is also a shelf for books or manuals, and a locker for tools or spare parts.

The heads compartment is located forward of the saloon, across the full beam of the boat. It has a marine WC with holding tank option, a washbasin with pressurized water system, a shower with electric pump-out option, a mirror, a towel rail, an opening deck hatch, and access to the seacocks.

Hull and Deck
The hull is made of fiberglass reinforced plastic (FRP), with balsa core sandwich construction for stiffness and insulation. The hull shape is optimized for speed and stability, with fine entry forward, moderate beam amidships, and flat sections aft. The hull has an external lead ballast fin keel that provides low center of gravity and good righting moment. The hull also has a molded-in antifouling strip that protects the waterline from marine growth.

The deck is also made of FRP, with balsa core sandwich construction for strength and rigidity. The deck has a molded-in non-slip surface that provides good grip and safety. The deck also has a raised coachroof that gives more headroom and light below, as well as a recessed foredeck that reduces windage and spray. The deck has solid teak toe rails, grab handles, and rubbing strake, as well as 316 high grade stainless steel stanchions, pulpit, pushpit, and guardrails.

The cockpit is spacious and comfortable, with contoured seats and coamings that provide good support and protection. The cockpit has a single wheel on a pedestal that gives good visibility and control. The cockpit also has a large locker to port that can store sails, fenders, or other gear, as well as a smaller locker to starboard that can store the battery or other items. The cockpit also has a teak grating on the sole that drains water quickly and prevents slipping.

The above text was drafted by 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.

Other sailboats in the Westerly range include:

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