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Review of J/124


Basic specs.

sail specifications
The J/124 is a large sailboat designed by the maritime architect Rodney S. Johnstone.

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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.

Interior
The boat is equipped with 6 berths.

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 boat can only enter major marinas as the draft is about 2.10 - 2.20 meter (6.89 - 7.19 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 J/124 is 1.95, indicating that this boat could - if evaluated by this formula alone - be accepted to participate in ocean races.


EU classification

J/124 holds one CE certification:

The boat is by European Union certified as Class A. OCEAN:
Designed for extended voyages where conditions may exceed wind force 8 (Beaufort scale) and significant wave heights of 4 m and above but excluding abnormal conditions, and vessels largely self-sufficient.


Theoretical Maximum Hull Speed

What is Theoretical Maximum Hull Speed?

The theoretical maximal speed of a displacement boat of this length is 8.1 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 J/124 is about 254 kg/cm, alternatively 1427 lbs/inch.
Meaning: if you load 254 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1427 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 J/124 is 20.3.

Low High 12% 0 50 100
Comparing this ratio with similar sailboats show that it is more comfortable than 12% of all similar sailboat designs. This is a comfort value significantly below average.


L/B (Length Beam Ratio)

What is L/B (Length Beam Ratio)?

The l/b ratio for J/124 is 3.59.

Wide Slim 79% 0 50 100
Compared with other similar sailboats it is slimmer than 79% of all other designs. It seems that the designer has chosen a significantly more speedy hull design.


Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for J/124 is 40%.

Low High 54% 0 50 100
This ballast ratio shows a righting moment that is higher than 54% 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 J/124 is 118 which categorizes this boat among 'ultra light racers'.

Heavy Light 93% 0 50 100
93% 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)

What is SA/D (Sail Area Displacement ratio)?

The SA/D for J/124 with ISO 8666 reference sail is 22.3, with a 135% genua the SA/D is 25.8.

Low High 96% 0 50 100
The SA/D ratio indicates that it is faster than 96% of all similar sailboat designs in light wind.


Over- / underrigged

Low High 96% 0 50 100
The J/124 has more rig than 96% of all similar sailboats, which indicates that the boat is significantly overrigged.


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 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.


Rig

Dimensions of sail for fractional rig.

mainsail specifications headsail specifications

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
UsageLengthDiameter
Mainsail halyard 38.2 m(125.2 feet)12 mm(1/2 inch)
Jib/genoa halyard38.2 m(125.2 feet)12 mm(1/2 inch)
Spinnaker halyard38.2 m(125.2 feet)12 mm(1/2 inch)
Jib sheet 12.4 m(40.7 feet)14 mm(0.55 inch)
Genoa sheet12.4 m(40.7 feet)14 mm(0.55 inch)
Mainsheet 31.0 m(101.7 feet)14 mm(0.55 inch)
Spinnaker sheet27.3 m(89.5 feet)14 mm(0.55 inch)
Cunningham5.2 m(17.0 feet)12 mm(1/2 inch)
Kickingstrap10.4 m(34.0 feet)12 mm(1/2 inch)
Clew-outhaul10.4 m(34.0 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.

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 J/124 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