Review of Compass 31

Compass 31
Compass 31 anno 1973.

Basic specs.

boat specifications
The Compass 31 is a motorsailer designed by the Danish maritime architect Tony Hansen in the early seventies. A few hundred boats have been produced. The Compass 31 is built by the Danish yard Sønderborg Yachtværft ApS.

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Both the hull and the deck 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.
The deck is a double deck which improves the indoor climate.

Interior of Compass 31 anno 1985.
The boat is equipped with 7-8 berths, a galley and toilet facility.

Cockpit of Compass 31 anno 1985.
The boat has a ketch rig.

Keel of Compass 31 anno 1985.
The keel is made of lead. Compared with iron, lead has the advantage of being 44% heavier, which allow a minor keel and hence less water resistance and higher speed. The boat can enter even shallow marinas as the draft is just about 1.40 - 1.50 meter (4.59 - 4.89 ft) dependent on the load. See immersion rate below.

Compass 31 is typical equipped with an inboard Volvo Penta engine at 36.0 hp (26 kW), which gives a max speed about 6.8 knots.
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 fibreglass has a capacity of 155 liters (40 US 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 Compass 31 is 1.77, 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 7.1 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 Compass 31 is about 176 kg/cm, alternative 988 lbs/inch.
Meaning: if you load 176 kg cargo on the boat then it will sink 1 cm. Alternative, if you load 988 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 22,000 boat types and 350,000 data points.

Motion Comfort Ratio
What is Motion Comfort Ratio (MCR)?
The Motion Comfort Ratio for Compass 31 is 29.3.

Low High 79% 0 50 100
Comparing this ratio with similar sailboats show that it is more comfortable than 79% of all similar sailboat designs. A comfort value significantly above average.

L/B (Length Beam Ratio)
What is L/B (Length Beam Ratio)?
The l/b ratio for Compass 31 is 3.06.

Slim Wide 58% 0 50 100
Compared with other similar sailboats it is more spacy than 58% 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 Compass 31 is 249 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 precice average ratio between displacement and length!


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 29m2 (312 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.

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 9.5 m(31.2 feet)12 mm(1/2 inch)
Genoa sheet9.5 m(31.2 feet)12 mm(1/2 inch)
Mainsheet 23.8 m(77.9 feet)12 mm(1/2 inch)
Spinnaker sheet20.9 m(68.6 feet)12 mm(1/2 inch)

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