Review of Alden O Class Mk II

Basic specs.

The Alden O Class Mk II is a small sailboat designed by the American maritime architect John Gale Alden in the mid twenties. A few hundred boats have been produced. The Alden O Class Mk II is built by the American yard Graves Yacht Yard.

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Hull

The hull is made of wood.

Rig

The boat equipped with a fractional rig. A fractional rig has smaller headsails which make tacking easier, which is an advantage for cruisers and racers, of course. The downside is that having the wind from behind often requires a genaker or a spinnaker for optimal speed.

Keel

The Alden O Class Mk II 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 sail close to the beach as the draft is just 0.29 - 0.39 meter (0.95 - 1.25 ft) dependent of 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 Alden O Class Mk II 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 5.3 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 Alden O Class Mk II is about 63 kg/cm, alternatively 357 lbs/inch.
Meaning: if you load 63 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 357 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 Alden O Class Mk II is 15.1.

Comparing this ratio with similar sailboats show that it is more comfortable than 88% 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 Alden O Class Mk II is 2.73.

Compared with other similar sailboats it is slimmer than 62% of all other designs. It seems that the designer has chosen a slightly more speedy hull design.

Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for Alden O Class Mk II is 27%.

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 Alden O Class Mk II is 243 which categorizes this boat among 'light crusers & offshore racers'.

15% 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)

SA/D (Sail Area Displacement ratio)
Indicates how fast the boat is in light wind:
- Cruising Boats have ratios 10-15
- Cruiser-Racers have ratios 16-20
- Racers have ratios above 20
- High-Performance Racers have ratios above 24
Sail-area/displacement ratio (SA/D ratio): 19.36

Maintenance

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	5.5 m	(18.2 feet)	8 mm	(5/16 inch)
Genoa sheet	5.5 m	(18.2 feet)	8 mm	(5/16 inch)
Mainsheet	13.8 m	(45.4 feet)	8 mm	(5/16 inch)
Spinnaker sheet	12.2 m	(40.0 feet)	8 mm	(5/16 inch)

Boat owner's ideas

This section is reserved boat owner's changes, 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

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References

[Ref 1]: ISO 8666 Small craft — Principal data.
[Ref 3]: ISO 12215-5 Small craft — Hull construction and scantlings.