Review of Bristol 31.1

Basic specs.

The Bristol 31.1 is a sailboat designed by the American maritime architect Ted Hood in the early eighties. The Bristol 31.1 is built by the American yard Bristol Yachts Inc..

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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.

Rig

The Bristol 31.1 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.

Keel

The Bristol 31.1 has been built with different keel alternatives.

CentreBoard

One option is a centreboard keel. A centreboard keel is a pivoting lifting keel, allowing to sail both coastal and inland waters.

The boat can enter even shallow marinas as the draft is just about 1.07 - 1.17 meter (3.51 - 3.81 ft) dependent on the load. See immersion rate below.

Fin keel

Another 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 boat can enter most marinas as the draft is just about 1.62 - 1.72 meter (5.31 - 5.61 ft) dependent on the load. See immersion rate below.

Engine

Bristol 31.1 may be equipped with an inboard Universal 18 diesel engine at 14 hp (10 kW). Calculated max speed is about 4.1 knots

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 Bristol 31.1 is 1.82, 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 6.7 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 Bristol 31.1 is about 156 kg/cm, alternatively 876 lbs/inch.
Meaning: if you load 156 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 876 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 Bristol 31.1 is 29.4.

Comparing this ratio with similar sailboats show that it is more comfortable than 79% 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 Bristol 31.1 is 3.05.

Compared with other similar sailboats it is more spacy than 58% of all other designs. It seems that the designer has chosen a slightly more spacy hull design.

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Bristol 31.1 is 330 which categorizes this boat among 'heavy cruisers'.

18% 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)

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

The SA/D for Bristol 31.1 with ISO 8666 reference sail is 14.5, with a 135% genua the SA/D is 17.6.

The SA/D ratio indicates that it is faster than 27% of all similar sailboat designs in light wind.

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 30m² (322 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

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.

**Guiding dimensions of running rig**
Usage	Length		Diameter
Mainsail halyard	27.8 m	(91.3 feet)	10 mm	(3/8 inch)
Jib/genoa halyard	27.8 m	(91.3 feet)	10 mm	(3/8 inch)
Spinnaker halyard	27.8 m	(91.3 feet)	10 mm	(3/8 inch)
Jib sheet	9.4 m	(31.0 feet)	12 mm	(1/2 inch)
Genoa sheet	9.4 m	(31.0 feet)	12 mm	(1/2 inch)
Mainsheet	23.6 m	(77.5 feet)	12 mm	(1/2 inch)
Spinnaker sheet	20.8 m	(68.2 feet)	12 mm	(1/2 inch)
Cunningham	3.1 m	(10.3 feet)	10 mm	(3/8 inch)
Kickingstrap	6.3 m	(20.6 feet)	10 mm	(3/8 inch)
Clew-outhaul	6.3 m	(20.6 feet)	10 mm	(3/8 inch)

Boat owner's ideas

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.

Finally

We are always looking for new photos. If you can contribute with photos for Bristol 31.1 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.