Review of B 31
Basic specs.
Looking for a new boat? Find a B 31 or similar boat for sale
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 boat is equipped with 6 berths.
Note: the boat has also been sold to be self-made/-interiored, which means that the quality of each boat may vary.
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.
The B 31 has been built with different keel alternatives.
Fin keel
One option is a fin keel. The fin keel is the most common keel and provides splendid manoeuvrability. The downside is that it has less directional stability than a long keel.
The keel is made of iron. Many people prefer lead keel in favour of iron. The main argument is that lead is much heavier than iron and a lead keel can therefore be made smaller which again result in less wet surface, i.e. less drag. In fact iron is quite heavy, just 30% less heavy than lead, so the advantage of a lead keel is often overstated. As the surface of a fin type keel is just a fraction of the total wet surface, the difference between an iron keel and a lead keel can in reality be ignored for cruising yachts.
B 31 can enter most marinas as the draft is just about 1.70 - 1.80 meter (5.58 - 5.88 ft) dependent on the load. See immersion rate below.
Fin keel
Another option is a fin keel.
This keel is also made of iron.
The boat can only enter major marinas as the draft is about 1.80 - 1.90 meter (5.91 - 6.21 ft) dependent on the load. See immersion rate below.
The boat is typically equipped with an inboard Yanmar diesel engine at 8 hp (5 kW). Calculated max speed is about 3.6 knots
The transmission is a shaft drive. A shaft drive will in the long run require less maintenance 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.
What is Capsize Screening Formula (CSF)?
The capsize screening value for B 31 is 1.83, 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 B 31 is about 125 kg/cm, alternatively 703 lbs/inch.
Meaning: if you load 125 kg cargo on the boat then it will sink 1 cm.
Alternatively, if you load 703 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.
What is Motion Comfort Ratio (MCR)?
The Motion Comfort Ratio for B 31 is 25.6.
What is L/B (Length Beam Ratio)?
The l/b ratio for B 31 is 3.38.
The ballast ratio for B 31 is 42%.
What is Displacement Length Ratio?
The DL-ratio for B 31 is 314 which categorizes this boat among 'medium weight cruisers'.
What is SA/D (Sail Area Displacement ratio)?
The SA/D for B 31 with ISO 8666 reference sail is 15.1, with a 135% genua the SA/D is 18.3.
Maintenance
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.
Dimensions of sail for masthead rig.
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.
| Usage | Length | Diameter | ||
| Mainsail halyard | 25.6 m | (83.8 feet) | 10 mm | (3/8 inch) |
| Jib/genoa halyard | 25.6 m | (83.8 feet) | 10 mm | (3/8 inch) |
| Spinnaker halyard | 25.6 m | (83.8 feet) | 10 mm | (3/8 inch) |
| Jib sheet | 9.3 m | (30.6 feet) | 12 mm | (1/2 inch) |
| Genoa sheet | 9.3 m | (30.6 feet) | 12 mm | (1/2 inch) |
| Mainsheet | 23.3 m | (76.5 feet) | 12 mm | (1/2 inch) |
| Spinnaker sheet | 20.5 m | (67.3 feet) | 12 mm | (1/2 inch) |
| Cunningham | 2.8 m | (9.2 feet) | 10 mm | (3/8 inch) |
| Kickingstrap | 5.6 m | (18.4 feet) | 10 mm | (3/8 inch) |
| Clew-outhaul | 5.6 m | (18.4 feet) | 10 mm | (3/8 inch) |
This section is reserved boat owner's modifications, 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.
We are always looking for new photos. If you can contribute with photos for B 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.