Review of Alpa 42

Basic specs.

sail specifications
The Alpa 42 aka Zuanelli 42 is a large sailboat designed by the American maritime architect bureau Sparkman & Stephens in the early seventies. Only a few boats have been produced. The Alpa 42 is built by the Italian yard Alpa.

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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.


The boat is equipped with 401.0 liter fresh water capacity.


The Alpa 42 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 only enter major marinas as the draft is about 1.85 - 1.95 meter (6.07 - 6.37 ft) dependent on the load. See immersion rate below.


Alpa 42 is typically equipped with a Perkins diesel engine.

The fuel tank has a capacity of 201.0 liters (53 US gallons, 44 imperial gallons).

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 Alpa 42 is 1.47, indicating that this boat could - if evaluated by this formula alone - 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 8.2 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 Alpa 42 is about 263 kg/cm, alternatively 1473 lbs/inch.
Meaning: if you load 263 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1473 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 Alpa 42 is 46.5.

Low High 99% 0 50 100
Comparing this ratio with similar sailboats show that it is more comfortable than 99% of all similar sailboat designs. This is a comfort value significantly above average.

L/B (Length Beam Ratio)

What is L/B (Length Beam Ratio)?

The l/b ratio for Alpa 42 is 3.50.

Wide Slim 69% 0 50 100
Compared with other similar sailboats it is slimmer than 69% of all other designs. It seems that the designer has chosen a slightly more speedy hull design.

Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for Alpa 42 is 34%.

Low High 24% 0 50 100
This ballast ratio shows a righting moment that is higher than 24% of all similar sailboat designs. A righting moment (ability to resist heeling) significantly below average.

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Alpa 42 is 244 which categorizes this boat among 'light crusers & offshore racers'.

Heavy Light 54% 0 50 100
54% 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 Alpa 42 with ISO 8666 reference sail is 10.9, with a 135% genua the SA/D is 13.0.

Low High 4% 0 50 100
The SA/D ratio indicates that it is faster than 4% of all similar sailboat designs in light wind.

Over- / underrigged

Low High 12% 0 50 100
The Alpa 42 has more rig than 12% of all similar sailboats, which indicates that the boat is significantly underrigged.


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 45m2 (484 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.

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 33.9 m(111.4 feet)12 mm(1/2 inch)
Jib/genoa halyard33.9 m(111.4 feet)12 mm(1/2 inch)
Spinnaker halyard33.9 m(111.4 feet)12 mm(1/2 inch)
Jib sheet 12.0 m(39.4 feet)14 mm(0.55 inch)
Genoa sheet12.0 m(39.4 feet)14 mm(0.55 inch)
Mainsheet 30.0 m(98.4 feet)14 mm(0.55 inch)
Spinnaker sheet26.4 m(86.6 feet)14 mm(0.55 inch)
Cunningham4.2 m(13.7 feet)12 mm(1/2 inch)
Kickingstrap8.4 m(27.5 feet)12 mm(1/2 inch)
Clew-outhaul8.4 m(27.5 feet)12 mm(1/2 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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