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Review of Inferno 31


Inferno 31
Inferno 31 anno 1989.

Basic specs.

sail specifications
The Inferno 31 aka Crown 31 or Finngulf 31 is a sailboat designed by the Swedish maritime architect Håkan Södergren in the early eighties.

Looking for a new boat? Find a Inferno 31 or similar boat for sale

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.

Rig
The boat equipped with a fractional rig. A fractional rig has smaller headsails which make tacking easier, which is an advantage for cruisers and racers, of course. The downside is that having the wind from behind often requires a genaker or a spinnaker for optimal speed.

Keel

The Inferno 31 is equipped with a fin keel. A boat with a fin keel is more manoeuvrable but has less directional stability than a similar boat with a long keel.

The keel is made of lead. Compared with iron, lead has the advantage of being 44% heavier, which allows a smaller keel and hence less water resistance and higher speed.

The boat can enter most marinas as the draft is just about 1.65 - 1.75 meter (5.41 - 5.71 ft) dependent on the load. See immersion rate below.


Engine

The boat is typically equipped with an inboard Volvo Penta MD2020 diesel engine.

The transmission is a saildrive.


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 Inferno 31 is 1.86, 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 6.8 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 Inferno 31 is about 156 kg/cm, alternatively 877 lbs/inch.
Meaning: if you load 156 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 877 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 Inferno 31 is 25.4.

Low High 58% 0 50 100
Comparing this ratio with similar sailboats show that it is more comfortable than 58% 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 Inferno 31 is 3.15.

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.


Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for Inferno 31 is 44%.

Low High 66% 0 50 100
This ballast ratio shows a righting moment that is higher than 66% of all similar sailboat designs. A righting moment (ability to resist heeling) just above average.


D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Inferno 31 is 252 which categorizes this boat among 'light crusers & offshore racers'.

Heavy Light 50% 0 50 100
50% of all similar sailboat designs are categorized as heavier. This boat has a precise average ratio between displacement and length!


SA/D (Sail Area Displacement ratio)

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

The SA/D for Inferno 31 with ISO 8666 reference sail is 17.8, with a 135% genua the SA/D is 20.5.

Low High 69% 0 50 100
The SA/D ratio indicates that it is faster than 69% of all similar sailboat designs in light wind.


Over- / underrigged

Low High 58% 0 50 100
The Inferno 31 has more rig than 58% of all similar sailboats, which indicates that the boat is slightly overrigged.


RSP (Relative Speed Performance)

What is Relative Speed Performance?

The Relative Speed Performance for Inferno 31 is 85

Slow Fast 85% 0 50 100
The relative speed performance is 85 which means that a it is faster than 85% of all similar sailboat designs.


Maintenance

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 27m2 (290 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.


Rig

Dimensions of sail for fractional rig.

mainsail specifications genoa specifications spinnaker 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
UsageLengthDiameter
Mainsail halyard 32.5 m(106.8 feet)10 mm(3/8 inch)
Jib/genoa halyard32.5 m(106.8 feet)10 mm(3/8 inch)
Spinnaker halyard32.5 m(106.8 feet)10 mm(3/8 inch)
Jib sheet 9.4 m(31.0 feet)12 mm(1/2 inch)
Genoa sheet9.4 m(31.0 feet)12 mm(1/2 inch)
Mainsheet 23.6 m(77.5 feet)12 mm(1/2 inch)
Spinnaker sheet20.8 m(68.2 feet)12 mm(1/2 inch)
Cunningham4.2 m(13.9 feet)10 mm(3/8 inch)
Kickingstrap8.5 m(27.9 feet)10 mm(3/8 inch)
Clew-outhaul8.5 m(27.9 feet)10 mm(3/8 inch)

Boat owner's ideas

This section shown boat owner's changes, improvements, etc. Here you might find inspiration for your boat.

Do you have changes/improvements you would like to share? Upload a photo and describe what to look for.



Finally

We are always looking for new photos. If you can contribute with photos for Inferno 31 it would be a great help.

If you have any comments to the review, improvement suggestions, or the like, feel free to contact us. Criticism helps us to improve.



References