Review of MacGregor 21

Basic specs.

The MacGregor 21 is a small sailboat designed by the maritime architect Roger MacGregor in the late seventies. The MacGregor 21 is built by the American yard MacGregor Yacht Corporation.

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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.

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 MacGregor 21 is 2.59, 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 5.8 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 MacGregor 21 is about 78 kg/cm, alternatively 440 lbs/inch.
Meaning: if you load 78 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 440 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 MacGregor 21 is 7.3.

Comparing this ratio with similar sailboats show that it is more comfortable than 10% 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 MacGregor 21 is 3.08.

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.

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for MacGregor 21 is 82 which categorizes this boat among 'ultra light racers'.

92% of all similar sailboat designs are categorized as heavier. A light displacement requires less sailarea and has higher accellerations.

SA/D (Sail Area Displacement ratio)

What is SA/D (Sail Area Displacement ratio)?

The SA/D for MacGregor 21 with ISO 8666 reference sail is 29.7, with a 135% genua the SA/D is 34.2.

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

Maintenance

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	18.8 m	(61.8 feet)	8 mm	(5/16 inch)
Jib/genoa halyard	18.8 m	(61.8 feet)	8 mm	(5/16 inch)
Spinnaker halyard	18.8 m	(61.8 feet)	8 mm	(5/16 inch)
Jib sheet	6.4 m	(21.0 feet)	10 mm	(3/8 inch)
Genoa sheet	6.4 m	(21.0 feet)	10 mm	(3/8 inch)
Mainsheet	16.0 m	(52.5 feet)	10 mm	(3/8 inch)
Spinnaker sheet	14.1 m	(46.2 feet)	10 mm	(3/8 inch)
Cunningham	3.0 m	(10.0 feet)	8 mm	(5/16 inch)
Kickingstrap	6.1 m	(20.0 feet)	8 mm	(5/16 inch)
Clew-outhaul	6.1 m	(20.0 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.

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Finally

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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.