Review of Snapdragon 747

Basic specs.

The Snapdragon 747 is a small sailboat designed by the maritime architect bureau Thames Structural Plastics together with Thomas Marine Inc. also from in the mid sixties. The Snapdragon 747 is built by the British yard Thames Marine 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.

Rig

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.

Keel

The Snapdragon 747 is equipped with a bilge keel. A bilge keel is a double keel, which allows the boat to be beached. Bilge keels are the most popular keel for tidal waters.

The boat can enter even shallow marinas as the draft is just about 0.76 - 0.86 meter (2.49 - 2.79 ft) dependent on the load. See immersion rate below.

Engine

The boat is typically equipped with an inboard Yanmar YS8 diesel engine.

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 Snapdragon 747 is 2.07, 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 6.1 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 Snapdragon 747 is about 102 kg/cm, alternatively 572 lbs/inch.
Meaning: if you load 102 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 572 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 Snapdragon 747 is 16.4.

Comparing this ratio with similar sailboats show that it is more comfortable than 46% 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 Snapdragon 747 is 3.06.

Compared with other similar sailboats it is slimmer than 62% of all other designs. It seems that the designer has chosen a slightly more speedy hull design.

Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for Snapdragon 747 is 42%.

This ballast ratio shows a righting moment that is higher than 62% 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 Snapdragon 747 is 191 which categorizes this boat among 'light racers'.

62% 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)

SA/D (Sail Area Displacement ratio)
Indicates how fast the boat is in light wind:
- Cruising Boats have ratios 10-15
- Cruiser-Racers have ratios 16-20
- Racers have ratios above 20
- High-Performance Racers have ratios above 24
Sail-area/displacement ratio (SA/D ratio): 14.38

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 15m² (161 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

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
Jib sheet	7.5 m	(24.5 feet)	10 mm	(3/8 inch)
Genoa sheet	7.5 m	(24.5 feet)	10 mm	(3/8 inch)
Mainsheet	18.7 m	(61.3 feet)	10 mm	(3/8 inch)
Spinnaker sheet	16.4 m	(53.9 feet)	10 mm	(3/8 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 Snapdragon 747 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.