Review of B 31 Mark II
Basic specs.
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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 deck is a sandwich construction 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 boat is equipped with 6 berths, a galley, 100.0 liter fresh water capacity 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.
The B 31 Mark II is 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.
B 31 Mark II may be equipped with an inboard Yanmar 2GM diesel engine at 15 hp (11 kW). The speed is 7.0 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.
The fuel tank, which is made of stainless steel, has a capacity of 30.0 liters (7 US gallons, 6 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.
What is Capsize Screening Formula (CSF)?
The capsize screening value for B 31 Mark II 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 Mark II 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 Mark II is 22.5 - 25.6.
What is L/B (Length Beam Ratio)?
The l/b ratio for B 31 Mark II is 3.38.
What is Displacement Length Ratio?
The DL-ratio for B 31 Mark II is 295 which categorizes this boat among 'medium weight cruisers'.
What is Relative Speed Performance?
The Relative Speed Performance for B 31 Mark II is 21
Maintenance
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 | ||
| 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) |
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