Review of B 31 Mark II

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 double deck which improves the indoor climate.

The boat is equipped with 6 berths, a galley and toilet facility.
The headroom is above average
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.

B 31 Mark II is typically equipped with an inboard Yanmar 2GM diesel engine at 15.0 hp (11 kW), which gives a max speed about 4.9 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 stainless steel has a capacity of 30.0 liters (7 US gallons, 6 imperial gallons).

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.

What is Motion Comfort Ratio (MCR)?

The Motion Comfort Ratio for B 31 Mark II is 22.5 - 25.6.

Comparing this ratio with similar sailboats show that it is more comfortable than 62% of all similar sailboat designs. This comfort value is just above average.

What is L/B (Length Beam Ratio)?

The l/b ratio for B 31 Mark II is 3.38.

Compared with other similar sailboats it is slimmer than 76% 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 B 31 Mark II is 295 which categorizes this boat among 'medium weight cruisers'.

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.

What is Relative Speed Performance?

The Relative Speed Performance for B 31 Mark II is 21

The relative speed performance is 21 which means that a it is faster than 21% of all similar sailboat designs.

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.

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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.