Review of J/120

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

The J/120 is 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 gennaker or a spinnaker for optimal speed.

The J/120 has been built with different keel alternatives.

Fin keel

The J/120 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 full 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 2.12 - 2.22 meter (6.96 - 7.26 ft) dependent on the load. See immersion rate below.

Unknown keel type

The boat can enter most marinas as the draft is just about 1.54 - 1.64 meter (5.05 - 5.35 ft) dependent on the load. See immersion rate below.

J/120 may be equipped with an inboard Yanmar diesel engine at 40 hp (29 kW).

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.

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.

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.

What is a Ballast Ratio?

The ballast ratio for J/120 is 46%.

This ballast ratio shows a righting moment that is higher than 82% of all similar sailboat designs. A righting moment (ability to resist heeling) significantly above average.

The J/120 has more rig than 85% of all similar sailboats, which indicates that the boat is significantly overrigged.

When buying anti-fouling bottom paint, it's nice to know how much to buy. The surface of the wet bottom is about 46m² (495 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.

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.

This section is reserved boat owner's modifications, 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.

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.

[Ref 1]: ISO 8666 Small craft — Principal data.
[Ref 3]: ISO 12215-5 Small craft — Hull construction and scantlings.