Review of J/39
Basic specs.
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The hull is made of fibreglass. Generally, a hull made of fibreglass requires only a minimum of maintenance during the sailing season.
The boat is equipped with 2 cabins and 8 berths.
The J/39 is 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.
Fin keel
The J/39 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 2.20 - 2.30 meter (7.22 - 7.52 ft) dependent on the load. See immersion rate below.
J/39 may be equipped with an inboard Yanmar 3GM30 diesel engine at 27 hp (20 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.
What is Theoretical Maximum Hull Speed?
The theoretical maximal speed of a displacement boat of this length is 7.6 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/39 is about 271 kg/cm, alternatively 1519 lbs/inch.
Meaning: if you load 271 kg cargo on the boat then it will sink 1 cm.
Alternatively, if you load 1519 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.
What is L/B (Length Beam Ratio)?
The l/b ratio for J/39 is 2.94.
The ballast ratio for J/39 is 46%.
Maintenance
When buying anti-fouling bottom paint, it's nice to know how much to buy.
The surface of the wet bottom is about 47m2 (505 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 masthead 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.
| Usage | Length | Diameter | ||
| Mainsail halyard | 37.3 m | (122.3 feet) | 12 mm | (1/2 inch) |
| Jib/genoa halyard | 37.3 m | (122.3 feet) | 12 mm | (1/2 inch) |
| Spinnaker halyard | 37.3 m | (122.3 feet) | 12 mm | (1/2 inch) |
| Jib sheet | 12.0 m | (39.5 feet) | 14 mm | (0.55 inch) |
| Genoa sheet | 12.0 m | (39.5 feet) | 14 mm | (0.55 inch) |
| Mainsheet | 30.1 m | (98.8 feet) | 14 mm | (0.55 inch) |
| Spinnaker sheet | 26.5 m | (86.9 feet) | 14 mm | (0.55 inch) |
| Cunningham | 5.0 m | (16.3 feet) | 12 mm | (1/2 inch) |
| Kickingstrap | 9.9 m | (32.6 feet) | 12 mm | (1/2 inch) |
| Clew-outhaul | 9.9 m | (32.6 feet) | 12 mm | (1/2 inch) |
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