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Review of Aurora 21


Basic specs.

sail specifications
The Aurora 21 is a small sailboat designed by the American maritime architect Ted Carpentier in the late fifties. Several hundred boats have been produced. The Aurora 21 is built by Henry McCune.

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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. And outside the sailing season, just bottom cleaning and perhaps anti-fouling painting once a year - a few hours of work, that's all.


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 Aurora 21 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 keel is made of iron. Many people prefer lead keel in favour of iron. The main argument is that lead is much heavier than iron and a lead keel can therefore be made smaller which again result in less wet surface, i.e. less drag. In fact iron is quite heavy, just 30% less heavy than lead, so the advantage of a lead keel is often overstated. As the surface of a fin type keel is just a fraction of the total wet surface, the difference between an iron keel and a lead keel can in reality be ignored for cruising yachts.

The boat can enter even shallow marinas as the draft is just about 0.91 - 1.01 meter (2.99 - 3.29 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 Aurora 21 is 2.12, 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 Aurora 21 is about 61 kg/cm, alternatively 341 lbs/inch.
Meaning: if you load 61 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 341 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 Aurora 21 is 13.0.

Low High 46% 0 50 100
Comparing this ratio with similar sailboats show that it is more comfortable than 46% of all similar sailboat designs. This comfort value is just below average.


L/B (Length Beam Ratio)

What is L/B (Length Beam Ratio)?

The l/b ratio for Aurora 21 is 3.32.

Wide Slim 96% 0 50 100
Compared with other similar sailboats it is slimmer than 96% of all other designs. It seems that the designer has chosen a significantly more speedy hull design. This type of design is also referred to as 'needle'.


Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for Aurora 21 is 29%.

Low High 21% 0 50 100
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 Aurora 21 is 204 which categorizes this boat among 'light crusers & offshore racers'.

Heavy Light 42% 0 50 100
42% 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 Aurora 21 with ISO 8666 reference sail is 21.3, with a 135% genua the SA/D is 24.9.

Low High 76% 0 50 100
The SA/D ratio indicates that it is faster than 76% of all similar sailboat designs in light wind.


Over- / underrigged

Low High 100% 0 50 100
The Aurora 21 has more rig than 100% of all similar sailboats, which indicates that the boat is significantly 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 10m2 (107 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.

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 17.1 m(56.1 feet)8 mm(5/16 inch)
Jib/genoa halyard17.1 m(56.1 feet)8 mm(5/16 inch)
Spinnaker halyard17.1 m(56.1 feet)8 mm(5/16 inch)
Jib sheet 6.4 m(21.0 feet)10 mm(3/8 inch)
Genoa sheet6.4 m(21.0 feet)10 mm(3/8 inch)
Mainsheet 16.0 m(52.5 feet)10 mm(3/8 inch)
Spinnaker sheet14.1 m(46.2 feet)10 mm(3/8 inch)
Cunningham3.0 m(9.7 feet)8 mm(5/16 inch)
Kickingstrap5.9 m(19.4 feet)8 mm(5/16 inch)
Clew-outhaul5.9 m(19.4 feet)8 mm(5/16 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 Aurora 21 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