Review of Offshore 50

Basic specs.

The Offshore 50 also known as Alden 50 is a large sailboat designed by the American maritime architect bureau Alden Associates in the mid sixties. Only a few boats have been produced. The Offshore 50 is built by the Chinese yard Cheoy Lee Shipyard Ltd..

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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.

Interior

The boat is equipped with 568.0 liter fresh water capacity.

Rig

The Offshore 50 is equipped with a ketch rig. A ketch rig is generally considered easier to handle, because the sails are smaller, and because it can sail on most points to the wind with one sail completely taken down for repair or while reefing. The sail configuration of a ketch allows for better comfort and stability when sailing downwind or on a broad reach.

Keel

Full keel

The Offshore 50 is equipped with a long keel. A full keel provide a better directional stability than a similar boat with a fin keel; on the other hand, better directional stability means also that the boat is more difficult to handle in a harbour with less space.

The boat can only enter major marinas as the draft is about 1.98 - 2.08 meter (6.50 - 6.80 ft) dependent on the load. See immersion rate below.

Engine

Offshore 50 may be equipped with an inboard Perkins diesel engine at 100 hp (74 kW). Calculated max speed is about 7.5 knots

The fuel tank has a capacity of 643.0 liters (169 US gallons, 141 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 Offshore 50 is 1.62, indicating that this boat could - if evaluated by this formula alone - 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 7.9 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 Offshore 50 is about 283 kg/cm, alternatively 1590 lbs/inch.
Meaning: if you load 283 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 1590 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 Offshore 50 is 42.8.

Comparing this ratio with similar sailboats show that it is more comfortable than 82% 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 Offshore 50 is 3.83.

Compared with other similar sailboats it is slimmer than 85% of all other designs. It seems that the designer has chosen a significantly more speedy hull design.

Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for Offshore 50 is 41%.

This ballast ratio shows a righting moment that is higher than 79% of all similar sailboat designs. A righting moment (ability to resist heeling) significantly above average.

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Offshore 50 is 363 which categorizes this boat among 'heavy cruisers'.

5% 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 Offshore 50 with ISO 8666 reference sail is 13.9, with a 135% genua the SA/D is 16.3.

The SA/D ratio indicates that it is faster than 1% of all similar sailboat designs in light wind.

Over- / underrigged

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 47m² (505 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 ketch 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	37.3 m	(122.5 feet)	14 mm	(0.55 inch)
Jib/genoa halyard	37.3 m	(122.5 feet)	14 mm	(0.55 inch)
Spinnaker halyard	37.3 m	(122.5 feet)	14 mm	(0.55 inch)
Jib sheet	15.3 m	(50.3 feet)	16 mm	(5/8 inch)
Genoa sheet	15.3 m	(50.3 feet)	16 mm	(5/8 inch)
Mainsheet	38.4 m	(125.8 feet)	16 mm	(5/8 inch)
Spinnaker sheet	33.7 m	(110.7 feet)	16 mm	(5/8 inch)
Cunningham	5.8 m	(19.0 feet)	14 mm	(0.55 inch)
Kickingstrap	11.6 m	(38.1 feet)	14 mm	(0.55 inch)
Clew-outhaul	11.6 m	(38.1 feet)	14 mm	(0.55 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 Offshore 50 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.