Review of Irwin 33 Mk II

Basic specs.

The Irwin 33 Mk II is a sailboat designed by the maritime architect Ted Irwin in the mid seventies.

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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.

Rig

The Irwin 33 Mk II 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

The Irwin 33 Mk II has been built with different keel alternatives.

Fin keel

One option is 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 enter most marinas as the draft is just about 1.68 - 1.78 meter (5.51 - 5.81 ft) dependent on the load. See immersion rate below.

CentreBoard

Another option is 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.

Fin keel

Another option is 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.

Irwin 33 Mk II can enter even shallow marinas as the draft is just about 1.19 - 1.29 meter (3.90 - 4.20 ft) dependent on the load. See immersion rate below.

Engine

The boat may be equipped with an inboard Perkins engine

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 Irwin 33 Mk II is 1.95, 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 7.0 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 Irwin 33 Mk II is about 190 kg/cm, alternatively 1068 lbs/inch.
Meaning: if you load 190 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1068 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 Irwin 33 Mk II is 25.3.

Comparing this ratio with similar sailboats show that it is more comfortable than 54% of all similar sailboat designs. This comfort value is just above average.

L/B (Length Beam Ratio)

What is L/B (Length Beam Ratio)?

The l/b ratio for Irwin 33 Mk II is 2.96.

Compared with other similar sailboats it is more spacy than 73% 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 Irwin 33 Mk II is 35%.

This ballast ratio shows a righting moment that is higher than 21% of all similar sailboat designs. A righting moment (ability to resist heeling) significantly below average.

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Irwin 33 Mk II is 256 which categorizes this boat among 'light crusers & offshore racers'.

46% 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 Irwin 33 Mk II with ISO 8666 reference sail is 15.0, with a 135% genua the SA/D is 18.1.

The SA/D ratio indicates that it is faster than 24% of all similar sailboat designs in light wind.

Over- / underrigged

The Irwin 33 Mk II has more rig than 62% 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 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.

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	28.4 m	(93.0 feet)	10 mm	(3/8 inch)
Jib/genoa halyard	28.4 m	(93.0 feet)	10 mm	(3/8 inch)
Spinnaker halyard	28.4 m	(93.0 feet)	10 mm	(3/8 inch)
Jib sheet	10.1 m	(33.0 feet)	12 mm	(1/2 inch)
Genoa sheet	10.1 m	(33.0 feet)	12 mm	(1/2 inch)
Mainsheet	25.2 m	(82.5 feet)	12 mm	(1/2 inch)
Spinnaker sheet	22.1 m	(72.6 feet)	12 mm	(1/2 inch)
Cunningham	3.4 m	(11.0 feet)	10 mm	(3/8 inch)
Kickingstrap	6.7 m	(22.0 feet)	10 mm	(3/8 inch)
Clew-outhaul	6.7 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.

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Finally

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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.