Review of Sonata 7

Basic specs.

The Sonata 7 aka Hunter Sonata is a small sailboat designed by the British maritime architect David Thomas in the mid seventies. Several hundred boats have been produced. The Sonata 7 is built by the British yard Hunter Boats Ltd..

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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.

Interior

The interior is like most other boats made of teak.
The boat is equipped with 2 cabins, 4 berths, a galley and toilet facility.

Rig

The boat equipped with a fractional rig. A fractional rig has smaller headsails which make tacking easier, which is an advantage for cruisers and racers, of course. The downside is that having the wind from behind often requires a genaker or a spinnaker for optimal speed.

Keel

The Sonata 7 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 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.

The boat can enter even shallow marinas as the draft is just about 1.40 - 1.50 meter (4.59 - 4.89 ft) dependent on the load. See immersion rate below.

Engine

An outboard motor is often used on this boat. In that case Sonata 7 will typically require a power of 3 - 4 hp, alternatively 56 - 67 lbs thrust if you prefer an electrical motor. Electric outboards are becoming popular for sailboat owners who want clean instant power with less noise and no exhaust fumes.

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 Sonata 7 is 2.45, indicating that this boat would not 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 5.7 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 Sonata 7 is about 98 kg/cm, alternatively 552 lbs/inch.
Meaning: if you load 98 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 552 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 Sonata 7 is 11.1 - 12.6.

Comparing this ratio with similar sailboats show that it is more comfortable than 42% of all similar sailboat designs. This comfort value is just below average.

L/B (Length Beam Ratio)

What is L/B (Length Beam Ratio)?

The l/b ratio for Sonata 7 is 2.48.

Compared with other similar sailboats it is more spacy than 85% of all other designs. It seems that the designer has chosen a significantly more spacy hull design.

Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for Sonata 7 is 39%.

This ballast ratio shows a righting moment that is higher than 54% of all similar sailboat designs. A righting moment (ability to resist heeling) just above average.

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Sonata 7 is 189 which categorizes this boat among 'light racers'.

54% of all similar sailboat designs are categorized as heavier. A light displacement requires less sailarea and has higher accellerations.

SA/D (Sail Area Displacement ratio)

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

The SA/D for Sonata 7 with ISO 8666 reference sail is 16.4, with a 135% genua the SA/D is 19.0.

The SA/D ratio indicates that it is faster than 34% of all similar sailboat designs in light wind.

Over- / underrigged

The Sonata 7 has more rig than 54% of all similar sailboats, which indicates that the boat is slightly overrigged.

RSP (Relative Speed Performance)

What is Relative Speed Performance?

The Relative Speed Performance for Sonata 7 is 76

The relative speed performance is 76 which means that a it is faster than 76% of all similar sailboat designs.

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 17m² (182 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 fractional 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	21.1 m	(69.3 feet)	8 mm	(5/16 inch)
Jib/genoa halyard	21.1 m	(69.3 feet)	8 mm	(5/16 inch)
Spinnaker halyard	21.1 m	(69.3 feet)	8 mm	(5/16 inch)
Jib sheet	6.5 m	(21.4 feet)	10 mm	(3/8 inch)
Genoa sheet	6.5 m	(21.4 feet)	10 mm	(3/8 inch)
Mainsheet	16.3 m	(53.6 feet)	10 mm	(3/8 inch)
Spinnaker sheet	14.4 m	(47.1 feet)	10 mm	(3/8 inch)
Cunningham	2.6 m	(8.5 feet)	8 mm	(5/16 inch)
Kickingstrap	5.2 m	(17.1 feet)	8 mm	(5/16 inch)
Clew-outhaul	5.2 m	(17.1 feet)	8 mm	(5/16 inch)

Boat owner's ideas

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.

Finally

We are always looking for new photos. If you can contribute with photos for Sonata 7 (Thomas) 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.