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Review of Jon 33

Jon 33
Jon 33 anno 1980. Bella Vita i Utklippans hamn

Basic specs.

sail specifications
The Jon 33 is a sailboat designed by the maritime architect Jorma Nyman.

Looking for a new boat? Find a Jon 33 or similar boat for sale

Rig

The Jon 33 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.


Keel

Unknown keel type

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 1.85 - 1.95 meter (6.07 - 6.37 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 Jon 33 is 1.85, indicating that this boat could - if evaluated by this formula alone - be accepted to participate in ocean races.


Theoretical Maximum Hull Speed

What is Theoretical Maximum Hull Speed?

The theoretical maximal speed of a displacement boat of this length is 6.9 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.


Immersion rate

The immersion rate is defined as the weight required to sink the boat a certain level. The immersion rate for Jon 33 is about 181 kg/cm, alternatively 1015 lbs/inch.
Meaning: if you load 181 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1015 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 Jon 33 is 29.3.

Low High 76% 0 50 100
Comparing this ratio with similar sailboats show that it is more comfortable than 76% of all similar sailboat designs. This is a comfort value significantly above average.


L/B (Length Beam Ratio)

What is L/B (Length Beam Ratio)?

The l/b ratio for Jon 33 is 3.01.

Slim Wide 69% 0 50 100
Compared with other similar sailboats it is more spacy than 69% 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 Jon 33 is 41%.

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


D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Jon 33 is 314 which categorizes this boat among 'medium weight cruisers'.

Heavy Light 21% 0 50 100
21% of all similar sailboat designs are categorized as heavier. A heavy displacement combined with smaller water plane area has lower acceleration and is more comfortable.


SA/D (Sail Area Displacement ratio)

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

The SA/D for Jon 33 with ISO 8666 reference sail is 14.6, with a 135% genua the SA/D is 17.6.

Low High 21% 0 50 100
The SA/D ratio indicates that it is faster than 21% of all similar sailboat designs in light wind.


Over- / underrigged

Low High 24% 0 50 100
The Jon 33 has more rig than 24% of all similar sailboats, which indicates that the boat is significantly underrigged.


RSP (Relative Speed Performance)

What is Relative Speed Performance?

The Relative Speed Performance for Jon 33 is 54

Slow Fast 54% 0 50 100
The relative speed performance is 54 which means that a it is faster than 54% of all similar sailboat designs.


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 32m2 (344 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 masthead rig.

mainsail specifications genoa specifications spinnaker 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 31.3 m(102.7 feet)10 mm(3/8 inch)
Jib/genoa halyard31.3 m(102.7 feet)10 mm(3/8 inch)
Spinnaker halyard31.3 m(102.7 feet)10 mm(3/8 inch)
Jib sheet 10.1 m(33.0 feet)12 mm(1/2 inch)
Genoa sheet10.1 m(33.0 feet)12 mm(1/2 inch)
Mainsheet 25.2 m(82.6 feet)12 mm(1/2 inch)
Spinnaker sheet22.2 m(72.7 feet)12 mm(1/2 inch)
Cunningham3.4 m(11.0 feet)10 mm(3/8 inch)
Kickingstrap6.7 m(22.0 feet)10 mm(3/8 inch)
Clew-outhaul6.7 m(22.0 feet)10 mm(3/8 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 Jon 33 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.