Review of J/108

Basic specs.

The J/108 is a 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.
The hull is a double hull which improves the indoor climate. Especially when the water is colder than the air in the cabin, then the double hull insulates against cold water and reduce the condense water in the cabin.

Interior

The boat is equipped with 4 berths and 150.0 liter fresh water capacity.

Rig

The J/108 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.

Keel

CentreBoard

The J/108 is equipped with a centreboard keel. A centreboard keel is a pivoting lifting keel, allowing to sail both coastal and inland waters.

The boat can enter even shallow marinas as the draft is just about 1.22 - 1.32 meter (4.00 - 4.30 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/108 is 2.05, indicating that this boat would not be accepted to participate in ocean races.

EU classification

J/108 holds a 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 7.4 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/108 is about 218 kg/cm, alternatively 1224 lbs/inch.
Meaning: if you load 218 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1224 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/108 is 21.2.

Comparing this ratio with similar sailboats show that it is more comfortable than 21% 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/108 is 3.06.

Compared with other similar sailboats it is more spacy than 66% of all other designs. It seems that the designer has chosen a slightly more spacy hull design.

Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for J/108 is 39%.

This ballast ratio shows a righting moment that is higher than 46% of all similar sailboat designs. A righting moment (ability to resist heeling) just below average.

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for J/108 is 179 which categorizes this boat among 'light racers'.

82% 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/108 with ISO 8666 reference sail is 19.0, with a 135% genua the SA/D is 22.3.

The SA/D ratio indicates that it is faster than 79% of all similar sailboat designs in light wind.

Over- / underrigged

The J/108 has more rig than 66% of all similar sailboats, which indicates that the boat is slightly 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 39m² (419 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.

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	32.8 m	(107.8 feet)	12 mm	(1/2 inch)
Jib/genoa halyard	32.8 m	(107.8 feet)	12 mm	(1/2 inch)
Spinnaker halyard	32.8 m	(107.8 feet)	12 mm	(1/2 inch)
Jib sheet	10.8 m	(35.3 feet)	14 mm	(0.55 inch)
Genoa sheet	10.8 m	(35.3 feet)	14 mm	(0.55 inch)
Mainsheet	26.9 m	(88.2 feet)	14 mm	(0.55 inch)
Spinnaker sheet	23.7 m	(77.6 feet)	14 mm	(0.55 inch)
Cunningham	4.5 m	(14.8 feet)	12 mm	(1/2 inch)
Kickingstrap	9.0 m	(29.7 feet)	12 mm	(1/2 inch)
Clew-outhaul	9.0 m	(29.7 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/108 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.