Review of Classic 31

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 Classic 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 boat can enter even shallow marinas as the draft is just about 1.37 - 1.47 meter (4.49 - 4.79 ft) dependent on the load. See immersion rate below.

The boat is typically equipped with an inboard Universal Atomic 4 gasoline engine at 30.0 hp (22 kW), which gives a max speed about 6.2 knots.

What is Capsize Screening Formula (CSF)?

The capsize screening value for Classic 31 is 1.63, indicating that this boat could - if evaluated by this formula alone - be accepted to participate in ocean races.

What is Theoretical Maximum Hull Speed?

The theoretical maximal speed of a displacement boat of this length is 6.3 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.

The immersion rate is defined as the weight required to sink the boat a certain level. The immersion rate for Classic 31 is about 120 kg/cm, alternatively 673 lbs/inch.
Meaning: if you load 120 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 673 lbs cargo on the boat it will sink 1 inch.

What is Motion Comfort Ratio (MCR)?

The Motion Comfort Ratio for Classic 31 is 33.4.

Comparing this ratio with similar sailboats show that it is more comfortable than 92% of all similar sailboat designs. This is a comfort value significantly above average.

What is L/B (Length Beam Ratio)?

The l/b ratio for Classic 31 is 3.57.

Compared with other similar sailboats it is slimmer than 86% of all other designs. It seems that the designer has chosen a significantly more speedy hull design.

What is Displacement Length Ratio?

The DL-ratio for Classic 31 is 386 which categorizes this boat among 'heavy cruisers'.

5% 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.

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

The SA/D for Classic 31 with ISO 8666 reference sail is 15.4, with a 135% genua the SA/D is 18.5.

The SA/D ratio indicates that it is faster than 38% of all similar sailboat designs in light wind.

When buying anti-fouling bottom paint, it's nice to know how much to buy. The surface of the wet bottom is about 20m² (215 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.

Dimensions of sail.

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.

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.

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

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