Review of Thompson T7

Basic specs.

The Thompson T7 aka Lightning 7 is a small sailboat designed by the maritime architect Steve Thompson in the late nineties.

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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 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 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 1.80 - 1.90 meter (5.91 - 6.21 ft) dependent on the load. See immersion rate below.

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 Thompson T7 is 2.94, indicating that this boat would not be accepted to participate in ocean races.

Immersion rate

The immersion rate is defined as the weight required to sink the boat a certain level. The immersion rate for Thompson T7 is about 117 kg/cm, alternatively 656 lbs/inch.
Meaning: if you load 117 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 656 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 Thompson T7 is 2.80.

Compared with other similar sailboats it is more spacy than 62% 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 Thompson T7 is 52%.

This ballast ratio shows a righting moment that is higher than 92% of all similar sailboat designs. A righting moment (ability to resist heeling) significantly above average.

Maintenance

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	7.0 m	(23.0 feet)	10 mm	(3/8 inch)
Genoa sheet	7.0 m	(23.0 feet)	10 mm	(3/8 inch)
Mainsheet	17.5 m	(57.4 feet)	10 mm	(3/8 inch)
Spinnaker sheet	15.4 m	(50.5 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.

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Finally

We are always looking for new photos. If you can contribute with photos for Thompson T7 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.