Review of Castle 550

Basic specs.

The Castle 550 is a small sailboat designed by the maritime architect Steven Douglas in the early eighties. A few hundred boats have been produced. The Castle 550 is built by the Australian yard Yacht Works Inc.

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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

Castle 550 with spinnaker.

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

DaggerBoard

The Castle 550 is equipped with a daggerboard keel. A daggerboard is a lifting keel that can be lowered and raised, allowing the boat to enter shallow waters as well.

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 Castle 550 is 3.05, 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 5.4 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 Castle 550 is about 78 kg/cm, alternatively 439 lbs/inch.
Meaning: if you load 78 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 439 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 Castle 550 is 6.5.

Comparing this ratio with similar sailboats show that it is more comfortable than 15% 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 Castle 550 is 2.28.

Compared with other similar sailboats it is more spacy than 88% of all other designs. It seems that the designer has chosen a significantly more spacy hull design.

Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for Castle 550 is 25%.

This ballast ratio shows a righting moment that is higher than 15% 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 Castle 550 is 119 which categorizes this boat among 'ultra light racers'.

76% of all similar sailboat designs are categorized as heavier. A light displacement requires less sailarea and has higher accellerations.

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	(18.0 feet)	8 mm	(5/16 inch)
Genoa sheet	5.5 m	(18.0 feet)	8 mm	(5/16 inch)
Mainsheet	13.7 m	(44.9 feet)	8 mm	(5/16 inch)
Spinnaker sheet	12.1 m	(39.6 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.

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Finally

We are always looking for new photos. If you can contribute with photos for Castle 550 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.