Review of Swan 431 Cruising

Basic specs.

The Swan 431 Cruising is a large sailboat designed by the American maritime architect bureau Sparkman & Stephens in the mid seventies. Less than 100 boats have been produced. The Swan 431 Cruising is built by the Finnish yard Oy Nautor AB.

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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.

Interior

The boat is equipped with 375.0 liter fresh water capacity.

Rig

The Swan 431 Cruising 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

Fin keel

The Swan 431 Cruising 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 full keel.

The keel is made of lead. Compared with iron, lead has the advantage of being 44% heavier, which allows a smaller keel and hence less water resistance and higher speed.

The boat can only enter major marinas as the draft is about 2.26 - 2.36 meter (7.41 - 7.71 ft) dependent on the load. See immersion rate below.

Engine

Swan 431 Cruising may be equipped with an inboard Perkins 4.108 M diesel engine at 37 hp (27 kW). Calculated max speed is about 5.1 knots

The fuel tank has a capacity of 150.0 liters (39 US gallons, 32 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.

Stability and Safety

What is Capsize Screening Formula (CSF)?

The capsize screening value for Swan 431 Cruising is 1.80, 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 7.7 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 Swan 431 Cruising is about 278 kg/cm, alternatively 1559 lbs/inch.
Meaning: if you load 278 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1559 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.

L/B (Length Beam Ratio)

What is L/B (Length Beam Ratio)?

The l/b ratio for Swan 431 Cruising is 3.22.

Compared with other similar sailboats it is more spacy than 66% of all other designs. It seems that the designer has chosen a slightly more spacy hull design.

Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for Swan 431 Cruising is 45%.

This ballast ratio shows a righting moment that is higher than 85% of all similar sailboat designs. A righting moment (ability to resist heeling) significantly above average.

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Swan 431 Cruising is 319 which categorizes this boat among 'medium weight cruisers'.

15% 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 Swan 431 Cruising with ISO 8666 reference sail is 16.1, with a 135% genua the SA/D is 19.5.

The SA/D ratio indicates that it is faster than 21% of all similar sailboat designs in light wind.

Over- / underrigged

The Swan 431 Cruising has more rig than 14% of all similar sailboats, which indicates that the boat is significantly underrigged.

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 48m² (516 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	41.9 m	(137.4 feet)	14 mm	(0.55 inch)
Jib/genoa halyard	41.9 m	(137.4 feet)	14 mm	(0.55 inch)
Spinnaker halyard	41.9 m	(137.4 feet)	14 mm	(0.55 inch)
Jib sheet	13.2 m	(43.2 feet)	16 mm	(5/8 inch)
Genoa sheet	13.2 m	(43.2 feet)	16 mm	(5/8 inch)
Mainsheet	33.0 m	(108.1 feet)	16 mm	(5/8 inch)
Spinnaker sheet	29.0 m	(95.1 feet)	16 mm	(5/8 inch)
Cunningham	4.2 m	(13.7 feet)	14 mm	(0.55 inch)
Kickingstrap	8.4 m	(27.5 feet)	14 mm	(0.55 inch)
Clew-outhaul	8.4 m	(27.5 feet)	14 mm	(0.55 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 Swan 431 Cruising 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.