Review of Alacrity 670

Basic specs.

sail specifications
The Alacrity 670 aka Alacrity 22 is a small sailboat designed by the maritime architect Frank V. Butler in the early seventies. Several hundred boats have been produced. The Alacrity 670 is built by the British yard Russell Marine Ltd..

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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. Teak has the advantage of being naturally very oily and therefore water-repellent, which is suitable on boats.
The boat is equipped with 4 berths and toilet facility.


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 Alacrity 670 is equipped with a fin keel. The fin keel is the most common keel and provides splendid manoeuvrability. The downside is that it has less directional stability than a long keel.

The boat can enter most marinas as the draft is just about 1.53 - 1.63 meter (5.02 - 5.32 ft) dependent on the load. See immersion rate below.


Alacrity 670 is typically equipped with an 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 Alacrity 670 is 2.52, 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 5.9 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 Alacrity 670 is about 92 kg/cm, alternatively 517 lbs/inch.
Meaning: if you load 92 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 517 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 Alacrity 670 is 9.1.

Low High 15% 0 50 100
Comparing this ratio with similar sailboats show that it is more comfortable than 15% of all similar sailboat designs. This is a comfort value significantly below average.

L/B (Length Beam Ratio)

What is L/B (Length Beam Ratio)?

The l/b ratio for Alacrity 670 is 2.85.

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

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Alacrity 670 is 111 which categorizes this boat among 'ultra light racers'.

Heavy Light 86% 0 50 100
86% of all similar sailboat designs are categorized as heavier. A light displacement requires less sailarea and has higher accellerations.

SA/D (Sail Area Displacement ratio)

What is SA/D (Sail Area Displacement ratio)?

The SA/D for Alacrity 670 with ISO 8666 reference sail is 22.2, with a 135% genua the SA/D is 26.1.

Low High 82% 0 50 100
The SA/D ratio indicates that it is faster than 82% of all similar sailboat designs in light wind.


Bottom Paint

When buying anti-fouling bottom paint, it's nice to know how much to buy. The surface of the wet bottom is about 17m2 (182 ft2).
Based on this, your favourite maritime shop can tell you the quantity you need.

Note: If you use a paint roller you will need more paint than if you use a paintbrush.


Dimensions of sail for masthead rig.

mainsail specifications headsail specifications

Are your sails worn out? You might find your next sail here: Sails for Sale

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
Mainsail halyard 17.3 m(56.8 feet)8 mm(5/16 inch)
Jib/genoa halyard17.3 m(56.8 feet)8 mm(5/16 inch)
Spinnaker halyard17.3 m(56.8 feet)8 mm(5/16 inch)
Jib sheet 6.7 m(21.9 feet)10 mm(3/8 inch)
Genoa sheet6.7 m(21.9 feet)10 mm(3/8 inch)
Mainsheet 16.6 m(54.6 feet)10 mm(3/8 inch)
Spinnaker sheet14.7 m(48.1 feet)10 mm(3/8 inch)
Cunningham3.0 m(9.7 feet)8 mm(5/16 inch)
Kickingstrap5.9 m(19.4 feet)8 mm(5/16 inch)
Clew-outhaul5.9 m(19.4 feet)8 mm(5/16 inch)

Boat owner's ideas

This section is reserved boat owner's modifications, improvements, etc. Here you might find (or contribute with) inspiration for your boat.

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