Review of Herreshoff 31 Cat ketch

Basic specs.

The Herreshoff 31 Cat ketch aka Cat Ketch 31 is a sailboat designed by the American maritime architect Halsey C. Herreshoff in the late seventies. A few hundred boats have been produced. The Herreshoff 31 Cat ketch is built by the American yard Cat Ketch Corp..

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Hull

The hull is made of wood.
Some boats has a hull made of Fibreglass.

Interior

The boat is equipped with 227.0 liter fresh water capacity.

Keel

Fin keel

The Herreshoff 31 Cat ketch is equipped with 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 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 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.

Engine

The Herreshoff 31 Cat ketch has been equipped with different engine alternatives.

Alternative 1:

Herreshoff 31 Cat ketch may be equipped with an inboard Yanmar diesel engine

Alternative 2:

The boat may be equipped with an inboard Nanni diesel engine

The fuel tank has a capacity of 70.0 liters (18 US gallons, 15 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 Herreshoff 31 Cat ketch is 2.11, indicating that this boat would not 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 7.1 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 Herreshoff 31 Cat ketch is about 180 kg/cm, alternatively 1008 lbs/inch.
Meaning: if you load 180 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1008 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 Herreshoff 31 Cat ketch is 17.9.

Comparing this ratio with similar sailboats show that it is more comfortable than 18% 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 Herreshoff 31 Cat ketch is 2.98.

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 Herreshoff 31 Cat ketch is 44%.

This ballast ratio shows a righting moment that is higher than 69% 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 Herreshoff 31 Cat ketch is 154 which categorizes this boat among 'light racers'.

88% of all similar sailboat designs are categorized as heavier. A light displacement requires less sailarea and has higher accellerations.

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 28m² (301 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

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
Jib sheet	9.4 m	(30.8 feet)	12 mm	(1/2 inch)
Genoa sheet	9.4 m	(30.8 feet)	12 mm	(1/2 inch)
Mainsheet	23.5 m	(77.1 feet)	12 mm	(1/2 inch)
Spinnaker sheet	20.7 m	(67.8 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 Herreshoff 31 Cat ketch 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.