The Westerly Corsair Sailboat
Specs & Key Performance Indicators

Published Specification for the Westerly Corsair

Keel & Rudder Configuration: Twin keel and skeg-hung rudder.
Hull Material: GRP (Glass Reinforced Plastic).
Length Overall: 10.97m (36'0")*.
Waterline Length: 8.84m (29'0")*.
Beam: 3.66m (12'0")*.
Draft: 1.22m (4'0")*.
Rig Type: Masthead Sloop.
Displacement: 6,486 kg (14,300 lbs)*.
Ballast: 2,404 kg (5,300 lbs)*.
Sail Area: 60.1m² (647ft²)*.
Water Tank Capacity: 227 liters (50 gallons).
Fuel Tank Capacity: 182 liters (40 gallons).
Hull Speed: Approximately 7.39 knots.
Designer: Laurent Giles.
Builder: Westerly Marine Construction Ltd.
Year First Built: 1983.
Year Last Built: 1992.
Number Built: Approximately 200.

* Used to derive the design ratios referred to later in this article - here's how they're calculated...

Sail Areas & Rig Dimensions

Sail Areas & Rig Dimensions

Main Sail Area: Approximately 24.15m² (260ft²).
Fore Triangle (Jib/Genoa) Area: Approximately 35.96m² (387ft²).
Total Sail Area (Main + 100% Fore Triangle): 60.11m² (647ft²).

I (Foresail Hoist Length): 13.90m (45'7").
J (Foresail Foot Length): 5.16m (16'11").
P (Mainsail Hoist Length): 12.00m (39'4").
E (Mainsail Foot Length): 4.00m (13'4").

Published Design Ratios
The Key Performance Indicators (KPIs)

Based on its design ratios, the Westerly Corsair is theoretically a stable, comfortable, and moderately performing cruising sailboat.

• The Sail Area/Displacement Ratio (17.56) suggests it's a moderate performance cruiser, offering a good balance of sail area for its weight. It should sail efficiently in light to moderate winds without being overly sensitive or demanding frequent sail changes, making it suitable for comfortable cruising.

• The Displacement/Length Ratio (287.95) indicates a moderately heavy displacement cruiser. This implies a boat designed for stability and comfort in varied sea conditions. It will have good momentum, allowing it to maintain speed through choppy waters, and will be less prone to sharp pitching and rolling than lighter designs. It won't be a speed demon, but it's built for a solid, steady ride.

• A Ballast/Displacement Ratio (37.07%) in this range suggests moderate to good initial stability. This means the boat will resist heeling when under sail, providing a more comfortable and reassuring experience for the crew, and allowing it to carry its sails effectively even in stronger winds.

• The Capsize Screening Formula (2.05) suggests that the Corsair is generally considered stable enough for offshore cruising. While slightly above the commonly cited "less prone to capsize" threshold of 2.0, this figure should be considered in the context of its twin keel design, which offers good initial stability.

• The Comfort Ratio (30.58) points to a comfortable cruising boat. This ratio indicates that the Westerly Corsair will likely have a relatively gentle and smooth motion in a seaway, a significant advantage for extended voyages or for those who prefer a less lively ride.

Overall, the design ratios paint a picture of the Westerly Corsair as a forgiving and capable boat for coastal and offshore cruising. Its twin keel design likely contributes to its comfortable motion and shallower draft, offering versatility for accessing more anchorages. It's built to prioritize a steady, comfortable ride and the ability to carry gear for extended periods.

But the Design Ratios Don't Tell the Whole Story...

While design ratios offer a useful starting point, they provide a limited and simplified view of a sailboat's actual characteristics:

• Oversimplification of Complex Design: Ratios reduce a boat's design to a few numbers, ignoring the intricate details of hull shape, keel and rudder foil design, appendage placement, and sail shape, all of which critically influence performance.

• Ignores Rigging and Sail Plan Nuances: They don't account for the type of rig (e.g., fractional vs. masthead), sail efficiency, or how effectively the sails are balanced and trimmed.

• No Indication of Build Quality: Ratios provide no information about the boat's structural integrity, stiffness, or the quality of its construction, which are vital for real-world performance and safety.

• Incomplete Stability Picture: While Ballast/Displacement and CSF offer insights, they don't capture dynamic stability, recovery from knockdown, or the full range of positive stability, which are influenced by hull form and ballast distribution.

• Excludes Human Factors: The skill and experience of the crew significantly impact how a boat performs, a factor entirely absent from design ratios.

• Static View, Not Dynamic Performance: Ratios don't consider changing environmental conditions like wave patterns, wind shifts, or currents, which constantly affect a boat's behavior.

• Subjectivity of "Comfort": The Comfort Ratio attempts to quantify comfort, but how a boat feels in a seaway is highly personal and influenced by many unquantifiable factors.

• Evolution of Design: Modern hull forms, such as planing designs, may not be accurately assessed by traditional ratios, which are based on older design principles.

• No Handling Characteristics: Ratios don't describe how a boat handles under power, its maneuverability, responsiveness at the helm, or issues like weather or lee helm.

In essence, design ratios are helpful for general comparisons and understanding a boat's theoretical leanings, but they are far from a complete picture. Actual sailing performance, handling, and comfort are the result of a complex interaction between design, construction, crew skill, and the environment.

Summary

The Westerly Corsair, designed by Laurent Giles and built by Westerly Marine Construction Ltd. from 1983 to 1992, is a 36 foot twin-keel, masthead sloop. It was known for its consistent design and comfortable cruising characteristics.

Its design ratios indicate it's a stable and moderately performing cruiser, well-suited for both coastal and offshore voyages, prioritizing a steady motion and load-carrying ability.

However, relying solely on these ratios provides an incomplete understanding, as they don't account for detailed design nuances, build quality, crew skill, or dynamic environmental factors that critically influence a sailboat's real-world performance.

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