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Review of Irwin 37 Mk IV

Basic specs.

sail specifications
The Irwin 37 Mk IV is a sailboat designed by the maritime architect Ted Irwin in the late seventies.

Here we would have liked to show you nice photos of the Irwin 37 Mk IV.
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Looking for a new boat? Find an Irwin 37 Mk IV or similar boat for sale

Hull

The hull is made of fibreglass. Generally, a hull made of fibreglass requires only a minimum of maintenance during the sailing season.


Interior

The boat is equipped with 707.0 liter fresh water capacity.


Keel

Fin keel

The Irwin 37 Mk IV is equipped with a fin keel. The fin keel is the most common keel and provides splendid manoeuvrability. The downside is that it has less directional stability than a long 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.


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 37 Mk IV is 1.70, 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 7.3 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 37 Mk IV is about 214 kg/cm, alternatively 1203 lbs/inch.
Meaning: if you load 214 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1203 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 37 Mk IV is 36.9.

Low High 90% 0 50 100
Comparing this ratio with similar sailboats show that it is more comfortable than 90% 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 Irwin 37 Mk IV is 3.21.

Slim Wide 54% 0 50 100
Compared with other similar sailboats it is more spacy than 54% 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 37 Mk IV is 33%.

Low High 18% 0 50 100
This ballast ratio shows a righting moment that is higher than 18% 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 37 Mk IV is 331 which categorizes this boat among 'heavy cruisers'.

Heavy Light 18% 0 50 100
18% 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 37 Mk IV with ISO 8666 reference sail is 13.6, with a 135% genua the SA/D is 16.4.

Low High 14% 0 50 100
The SA/D ratio indicates that it is faster than 14% of all similar sailboat designs in light wind.


Over- / underrigged

Low High 54% 0 50 100
The Irwin 37 Mk IV has more rig than 54% 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 36m2 (387 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 28.4 m(93.3 feet)12 mm(1/2 inch)
Jib/genoa halyard28.4 m(93.3 feet)12 mm(1/2 inch)
Spinnaker halyard28.4 m(93.3 feet)12 mm(1/2 inch)
Jib sheet 11.3 m(37.0 feet)14 mm(0.55 inch)
Genoa sheet11.3 m(37.0 feet)14 mm(0.55 inch)
Mainsheet 28.2 m(92.5 feet)14 mm(0.55 inch)
Spinnaker sheet24.8 m(81.4 feet)14 mm(0.55 inch)
Cunningham4.5 m(14.6 feet)12 mm(1/2 inch)
Kickingstrap8.9 m(29.2 feet)12 mm(1/2 inch)
Clew-outhaul8.9 m(29.2 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 Irwin 37 Mk IV 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.