Review of Venus 31

Venus 31
Venus 31 anno 1979.

Basic specs.

sail specifications
The Venus 31 is a motorsailer designed by the Danish maritime architect Palle Mortensen in the mid seventies. Less than 100 boats have been produced. The Venus 31 is built by the Danish yard Danish Yacht Export.

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Interior of Venus 31 anno 1979.
The boat is equipped with 6 berths, a galley and toilet facility.
Note: the boat has also been sold to be self-made/-interiored, which means that the quality of each boat may vary.
Galley of Venus 31.

Cockpit of Venus 31 anno 1978.
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 of Venus 31.

Venus 31 is typically equipped with an inboard Bukh DV20 diesel engine at 20.0 hp (14 kW), which gives a max speed about 5.1 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 185 liters (48 US gallons, 40 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 Venus 31 is 1.93, 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 Venus 31 is about 171 kg/cm, alternatively 959 lbs/inch.
Meaning: if you load 171 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 959 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 Venus 31 is 26.3.

Low High 66% 0 50 100
Comparing this ratio with similar sailboats show that it is more comfortable than 66% 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 Venus 31 is 2.86.

Slim Wide 76% 0 50 100
Compared with other similar sailboats it is more spacy than 76% of all other designs. It seems that the designer has chosen a significantly more spacy hull design.

D/L (Displacement Length Ratio)
What is Displacement Length Ratio?
The DL-ratio for Venus 31 is 293 which categorizes this boat among 'medium weight cruisers'.

Heavy Light 31% 0 50 100
31% of all similar sailboat designs are categorized as heavier. A heavy displacement combined with smaller water plane area has lower acceleration and is more comfortable.

RSP (Relative Speed Performance)
What is Relative Speed Performance?
The Relative Speed Performance for Venus 31 is 10

Slow Fast 10% 0 50 100
The relative speed performance is 10 which means that a it is faster than 10% of all similar sailboat designs. As this boat is a motor sailer, it is expected that the performance of a motor sailer for sail alone is lower than a dedicated sailboat.


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 9.4 m(30.8 feet)12 mm(1/2 inch)
Genoa sheet9.4 m(30.8 feet)12 mm(1/2 inch)
Mainsheet 23.5 m(76.9 feet)12 mm(1/2 inch)
Spinnaker sheet20.6 m(67.7 feet)12 mm(1/2 inch)

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