Review of J/120

Basic specs.

The J/120 is a large sailboat designed by the maritime architect Johnstone.

Here we would have liked to show you nice photos of the J/120.
If you have a photo you would like to share: Upload Image

Looking for a new boat? Find a J/120 or similar boat for sale

Hull

The hull is made of fibreglass. Generally, a hull made of fibreglass requires only a minimum of maintenance during the sailing season.

Engine

The boat is typically equipped with an inboard Yanmar diesel engine at 40.0 hp (29 kW).

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.

Theoretical Maximum Hull Speed

What is Theoretical Maximum Hull Speed?

The theoretical maximal speed of a displacement boat of this length is 7.9 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 J/120 is about 259 kg/cm, alternatively 1455 lbs/inch.
Meaning: if you load 259 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1455 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 J/120 is 3.33.

Compared with other similar sailboats it is slimmer than 54% of all other designs. It seems that the designer has chosen a slightly more speedy hull design.

Maintenance

Rig

Dimensions of sail.

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	36.7 m	(120.5 feet)	12 mm	(1/2 inch)
Jib/genoa halyard	36.7 m	(120.5 feet)	12 mm	(1/2 inch)
Spinnaker halyard	36.7 m	(120.5 feet)	12 mm	(1/2 inch)
Jib sheet	12.2 m	(40.0 feet)	14 mm	(0.55 inch)
Genoa sheet	12.2 m	(40.0 feet)	14 mm	(0.55 inch)
Mainsheet	30.5 m	(100.1 feet)	14 mm	(0.55 inch)
Spinnaker sheet	26.8 m	(88.1 feet)	14 mm	(0.55 inch)
Cunningham	5.4 m	(17.8 feet)	12 mm	(1/2 inch)
Kickingstrap	10.9 m	(35.6 feet)	12 mm	(1/2 inch)
Clew-outhaul	10.9 m	(35.6 feet)	12 mm	(1/2 inch)

Boat owner's ideas

This section is reserved boat owner's changes, 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 J/120 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.