Review of Cobra 750

Basic specs.

The Cobra 750 is a small sailboat designed by the British maritime architect David Feltham in the late seventies. Several hundred boats have been produced. The Cobra 750 is built by the British yard Cobra Yachts.

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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.

Interior

The boat is equipped with 45.0 liter fresh water capacity.

Rig

The Cobra 750 is 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

Bilge keel

The Cobra 750 is equipped with a bilge keel. A bilge keel is a double keel, which allows the boat to be beached. Bilge keels are the most popular keel for tidal waters.

The boat can enter even shallow marinas as the draft is just about 1.07 - 1.17 meter (3.51 - 3.81 ft) dependent on the load. See immersion rate below.

Engine

Cobra 750 may be equipped with an inboard Volvo Penta diesel engine at 10 hp (7 kW). Calculated max speed is about 4.3 knots

The fuel tank has a capacity of 30.0 liters (7 US gallons, 6 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 Cobra 750 is 2.15, 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 6.0 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 Cobra 750 is about 118 kg/cm, alternatively 666 lbs/inch.
Meaning: if you load 118 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 666 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 Cobra 750 is 20.3.

Comparing this ratio with similar sailboats show that it is more comfortable than 66% of all similar sailboat designs. This comfort value is just above average.

L/B (Length Beam Ratio)

What is L/B (Length Beam Ratio)?

The l/b ratio for Cobra 750 is 2.58.

Compared with other similar sailboats it is more spacy than 90% 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 Cobra 750 is 39%.

This ballast ratio shows a righting moment that is higher than 50% of all similar sailboat designs. This righting moment (ability to resist heeling) is spot on average!

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Cobra 750 is 336 which categorizes this boat among 'heavy cruisers'.

10% 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): 17.84

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 18m² (193 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

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	7.6 m	(25.0 feet)	10 mm	(3/8 inch)
Genoa sheet	7.6 m	(25.0 feet)	10 mm	(3/8 inch)
Mainsheet	19.1 m	(62.5 feet)	10 mm	(3/8 inch)
Spinnaker sheet	16.8 m	(55.0 feet)	10 mm	(3/8 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 Cobra 750 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.