Review of Contest 31

Basic specs.

The Contest 31 is a sailboat designed by the Dutch maritime architect Uus van Essen in the early seventies. A few hundred boats have been produced. The Contest 31 is built by the Dutch yard Conyplex N.V..

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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.

Interior

The interior is like many other boats made of mahogany.
The boat is equipped with 6 berths, a galley and toilet facility.

Cockpit

Cockpit of Contest 31 anno 1974.

Rig

Rig of Contest 31.

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 Contest 31 anno 1972.

The Contest 31 has been built with more than one type of keel.

One option is 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 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.

Engine

Contest 31 is typically equipped with an inboard Volvo Penta MD2B diesel engine at 25.0 hp (18 kW), which gives a max speed about 5.6 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.

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 Contest 31 is 1.70, 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 6.5 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 Contest 31 is about 135 kg/cm, alternatively 760 lbs/inch.
Meaning: if you load 135 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 760 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 Contest 31 is 32.0.

Comparing this ratio with similar sailboats show that it is more comfortable than 88% 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 Contest 31 is 3.35.

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.

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Contest 31 is 364 which categorizes this boat among 'heavy cruisers'.

10% 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.

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): 15.45

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 23m² (247 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

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	9.5 m	(31.2 feet)	12 mm	(1/2 inch)
Genoa sheet	9.5 m	(31.2 feet)	12 mm	(1/2 inch)
Mainsheet	23.8 m	(77.9 feet)	12 mm	(1/2 inch)
Spinnaker sheet	20.9 m	(68.6 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.

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

Finally

We are always looking for new photos. If you can contribute with photos for Contest 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

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