Review of Johnson 30

Basic specs.

The Johnson 30 is a motorsailer designed by the maritime architect Bo Johnsson. A few hundred boats have been produced.

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Interior

The boat is equipped with 4 berths and a galley.

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.

Engine

The boat is typically equipped with an inboard Volvo Penta MD 3B diesel engine at 36.0 hp (26 kW).

The transmission is a shaft drive. A shaft drive will in the long run require less maintenence than other types of drive e.g. a sail drive.

The fuel tank has a capacity of 300.0 liters (79 US gallons, 65 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 Johnson 30 is 1.86, indicating that this boat could - if evaluated by this formula alone - 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 Johnson 30 is about 194 kg/cm, alternatively 1087 lbs/inch.
Meaning: if you load 194 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1087 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 Johnson 30 is 2.92.

Compared with other similar sailboats it is more spacy than 69% of all other designs. It seems that the designer has chosen a slightly more spacy hull design.

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	9.2 m	(30.2 feet)	12 mm	(1/2 inch)
Genoa sheet	9.2 m	(30.2 feet)	12 mm	(1/2 inch)
Mainsheet	23.0 m	(75.5 feet)	12 mm	(1/2 inch)
Spinnaker sheet	20.2 m	(66.4 feet)	12 mm	(1/2 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 Johnson 30 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.