Review of Sirocco 31 Mk II

Basic specs.

The Sirocco 31 Mk II aka Sirocco 31 Mk2 is a sailboat designed by the British maritime architect Angus S. Primrose in the early seventies. The Sirocco 31 Mk II is built by the Spanish yard Mistral.

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Hull

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 hull is a double hull which improves the indoor climate. Especially when the water is colder than the air in the cabin, then the double hull insulates against cold water and reduce the condense water in the cabin.

Interior

The boat is equipped with one cabin, 5 berths, a galley and toilet facility.
The headroom is above average

Rig

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.

Keel

Keel of Sirocco 31 Mk II anno 1973.

Engine

The boat is typically equipped with an inboard Volvo Penta 2001 diesel engine at 9.0 hp (6 kW).

The transmission is a shaft drive. A shaft drive will in the long run require less maintenence than other types of drive e.g. a sail drive.

The fuel tank which is made of stainless steel has a capacity of 30 liters (7 US gallons, 6 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 Sirocco 31 Mk II is 1.96, indicating that this boat could - if evaluated by this formula alone - be accepted to participate in ocean races.

Immersion rate

The immersion rate is defined as the weight required to sink the boat a certain level. The immersion rate for Sirocco 31 Mk II is about 180 kg/cm, alternatively 1008 lbs/inch.
Meaning: if you load 180 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1008 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.

L/B (Length Beam Ratio)

What is L/B (Length Beam Ratio)?

The l/b ratio for Sirocco 31 Mk II is 3.43.

Compared with other similar sailboats it is slimmer than 76% of all other designs. It seems that the designer has chosen a significantly more speedy hull design.

SA/D (Sail Area Displacement ratio)

SA/D (Sail Area Displacement ratio)
Indicates how fast the boat is in light wind:
- Cruising Boats have ratios 10-15
- Cruiser-Racers have ratios 16-20
- Racers have ratios above 20
- High-Performance Racers have ratios above 24
Sail-area/displacement ratio (SA/D ratio): 14.27

Maintenance

Rig

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**
Usage	Length		Diameter
Jib sheet	9.6 m	(31.5 feet)	12 mm	(1/2 inch)
Genoa sheet	9.6 m	(31.5 feet)	12 mm	(1/2 inch)
Mainsheet	24.0 m	(78.7 feet)	12 mm	(1/2 inch)
Spinnaker sheet	21.1 m	(69.3 feet)	12 mm	(1/2 inch)

Boat owner's ideas

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

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Finally

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References

[Ref 1]: ISO 8666 Small craft — Principal data.
[Ref 3]: ISO 12215-5 Small craft — Hull construction and scantlings.