Review of Irwin 38 Mk I

Basic specs.

The Irwin 38 Mk I is a sailboat designed by the maritime architect Ted Irwin in the early seventies. The Irwin 38 Mk I is built by the American yard Irwin Yachts.

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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 boat 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 38 Mk I is equipped with a centerboard keel. A centerboard 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 1.14 - 1.24 meter (3.74 - 4.04 ft) dependent on the load. See immersion rate below.

Engine

The boat is typically equipped with an inboard Universal Atomic 4 gasoline engine at 30.0 hp (22 kW), which gives a max speed about 5.4 knots.

The fuel tank has a capacity of 114.0 liters (30 US gallons, 25 imperial gallons).

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 38 Mk I is 1.69, 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 38 Mk I is about 179 kg/cm, alternatively 1006 lbs/inch.
Meaning: if you load 179 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1006 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 38 Mk I is 33.7.

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 Irwin 38 Mk I is 3.60.

Compared with other similar sailboats it is slimmer than 82% of all other designs. It seems that the designer has chosen a significantly more speedy hull design.

Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for Irwin 38 Mk I is 42%.

This ballast ratio shows a righting moment that is higher than 62% of all similar sailboat designs. A righting moment (ability to resist heeling) just above average.

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Irwin 38 Mk I is 330 which categorizes this boat among 'heavy cruisers'.

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 38 Mk I with ISO 8666 reference sail is 15.7, with a 135% genua the SA/D is 18.8.

The SA/D ratio indicates that it is faster than 34% of all similar sailboat designs in light wind.

Over- / underrigged

The Irwin 38 Mk I has more rig than 12% of all similar sailboats, which indicates that the boat is significantly underrigged.

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 38m² (409 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	31.8 m	(104.2 feet)	12 mm	(1/2 inch)
Jib/genoa halyard	31.8 m	(104.2 feet)	12 mm	(1/2 inch)
Spinnaker halyard	31.8 m	(104.2 feet)	12 mm	(1/2 inch)
Jib sheet	11.5 m	(37.8 feet)	14 mm	(0.55 inch)
Genoa sheet	11.5 m	(37.8 feet)	14 mm	(0.55 inch)
Mainsheet	28.8 m	(94.4 feet)	14 mm	(0.55 inch)
Spinnaker sheet	25.3 m	(83.1 feet)	14 mm	(0.55 inch)
Cunningham	4.1 m	(13.5 feet)	12 mm	(1/2 inch)
Kickingstrap	8.2 m	(27.0 feet)	12 mm	(1/2 inch)
Clew-outhaul	8.2 m	(27.0 feet)	12 mm	(1/2 inch)

Boat owner's ideas

This section shown boat owner's changes, improvements, etc. Here you might find inspiration for your boat.

Do you have changes/improvements you would like to share? Upload a photo and describe what to look for.

Finally

We are always looking for new photos. If you can contribute with photos for Irwin 38 Mk I 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.