Review of Westerly Cirrus

Basic specs.

sail specifications
The Westerly Cirrus is a small sailboat designed in the late sixties.

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The hull is made of fibreglass. Generally, a hull made of fibreglass requires only a minimum of maintenance during the sailing season. And outside the sailing season, just bottom cleaning and perhaps anti-fouling painting once a year - a few hours of work, that's all.

The interior is like most other boats made of teak.
The boat is equipped with 5 berths, a galley and toilet facility.

Rig of Westerly Cirrus anno 1969.
The boat equipped with a masthead rig. The advantage of a masthead rig is its simplicity and the fact that a given sail area - compared with a fractional rig - can be carried lower and thus with less heeling moment.

The boat is typically equipped with an inboard engine.

Sailing characteristics

This section covers widely used rules of thumb to describe the sailing characteristics. Please note that even though the calculations are correct, the interpretation of the results might not be valid for extreme boats.

Stability and Safety
What is Capsize Screening Formula (CSF)?
The capsize screening value for Westerly Cirrus is 2.09, indicating that this boat would not be accepted to participate in ocean races.

Theoretical Maximum Hull Speed
What is Theoretical Maximum Hull Speed?
The theoretical maximal speed of a displacement boat of this length is 5.8 knots. The term "Theoretical Maximum Hull Speed" is widely used even though a boat can sail faster. The term shall be interpreted as above the theoretical speed a great additional power is necessary for a small gain in speed.

Immersion rate
The immersion rate is defined as the weight required to sink the boat a certain level. The immersion rate for Westerly Cirrus is about 94 kg/cm, alternatively 530 lbs/inch.
Meaning: if you load 94 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 530 lbs cargo on the boat it will sink 1 inch.

Sailing statistics

This section is statistical comparison with similar boats of the same category. The basis of the following statistical computations is our unique database with more than 26,000 different boat types and 350,000 data points.

Motion Comfort Ratio
What is Motion Comfort Ratio (MCR)?
The Motion Comfort Ratio for Westerly Cirrus is 17.3.

Low High 73% 0 50 100
Comparing this ratio with similar sailboats show that it is more comfortable than 73% of all similar sailboat designs. This comfort value is just above average.

L/B (Length Beam Ratio)
What is L/B (Length Beam Ratio)?
The l/b ratio for Westerly Cirrus is 2.75.

Slim Wide 62% 0 50 100
Compared with other similar sailboats it is more spacy than 62% of all other designs. It seems that the designer has chosen a slightly more spacy hull design.

D/L (Displacement Length Ratio)
What is Displacement Length Ratio?
The DL-ratio for Westerly Cirrus is 232 which categorizes this boat among 'light crusers & offshore racers'.

Heavy Light 34% 0 50 100
34% of all similar sailboat designs are categorized as heavier. A heavy displacement combined with smaller water plane area has lower acceleration and is more comfortable.

RSP (Relative Speed Performance)
What is Relative Speed Performance?
The Relative Speed Performance for Westerly Cirrus is 5

Slow Fast 5% 0 50 100
The relative speed performance is 5 which means that a it is faster than 5% of all similar sailboat designs.


If you need to renew parts of your running rig and is not quite sure of the dimensions, you may find the estimates computed below useful.

Guiding dimensions of running rig
Jib sheet 6.7 m(22.0 feet)10 mm(3/8 inch)
Genoa sheet6.7 m(22.0 feet)10 mm(3/8 inch)
Mainsheet 16.8 m(55.0 feet)10 mm(3/8 inch)
Spinnaker sheet14.7 m(48.4 feet)10 mm(3/8 inch)

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