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Review of J/125


Basic specs.

sail specifications
The J/125 is a large sailboat designed by the maritime architect Johnstone 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.


Keel

Fin keel

The J/125 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 boat can only enter major marinas as the draft is about 2.41 - 2.51 meter (7.91 - 8.21 ft) dependent on the load. See immersion rate below.


Engine

The boat may be equipped with an inboard Yanmar 3GM30CxSD20 diesel engine at 30 hp (22 kW).

The transmission is a saildrive.


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 8.2 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/125 is about 244 kg/cm, alternatively 1366 lbs/inch.
Meaning: if you load 244 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1366 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/125 is 3.87.

Wide Slim 95% 0 50 100
Compared with other similar sailboats it is slimmer than 95% of all other designs. It seems that the designer has chosen a significantly more speedy hull design. This type of design is also referred to as 'needle'.


Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for J/125 is 56%.

Low High 99% 0 50 100
This ballast ratio shows a righting moment that is higher than 99% of all similar sailboat designs. A righting moment (ability to resist heeling) significantly above average.


Over- / underrigged

Low High 95% 0 50 100
The J/125 has more rig than 95% 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 48m2 (516 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.

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 36.7 m(120.5 feet)12 mm(1/2 inch)
Jib/genoa halyard36.7 m(120.5 feet)12 mm(1/2 inch)
Spinnaker halyard36.7 m(120.5 feet)12 mm(1/2 inch)
Jib sheet 12.5 m(41.0 feet)14 mm(0.55 inch)
Genoa sheet12.5 m(41.0 feet)14 mm(0.55 inch)
Mainsheet 31.2 m(102.5 feet)14 mm(0.55 inch)
Spinnaker sheet27.5 m(90.2 feet)14 mm(0.55 inch)
Cunningham5.5 m(18.0 feet)12 mm(1/2 inch)
Kickingstrap11.0 m(36.0 feet)12 mm(1/2 inch)
Clew-outhaul11.0 m(36.0 feet)12 mm(1/2 inch)

Boat owner's ideas

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.



Finally

We are always looking for new photos. If you can contribute with photos for J/125 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