Review of Wight Mk I 31

Basic specs.

The Wight Mk I 31 is a sailboat designed by the British maritime architect C. S. J. Roy in the late sixties.

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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 151.0 liter fresh water capacity.

Rig

The Wight Mk I 31 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

Triple keel

The Wight Mk I 31 is equipped with a triple keel keel. A triple keel ia a bilge keel, but with the ballast in a center keel. Tripple keels are useful in tidal waters in which the boat can be beached.

The boat can enter even shallow marinas as the draft is just about 0.99 - 1.09 meter (3.25 - 3.55 ft) dependent on the load. See immersion rate below.

Engine

Wight Mk I 31 may be equipped with an inboard BMC diesel engine at 33 hp (24 kW). Calculated max speed is about 6.9 knots

The fuel tank has a capacity of 95.0 liters (25 US gallons, 20 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 Wight Mk I 31 is 1.81, 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 6.5 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 Wight Mk I 31 is about 137 kg/cm, alternatively 770 lbs/inch.
Meaning: if you load 137 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 770 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 Wight Mk I 31 is 27.1.

Comparing this ratio with similar sailboats show that it is more comfortable than 69% 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 Wight Mk I 31 is 3.24.

Compared with other similar sailboats it is slimmer than 62% of all other designs. It seems that the designer has chosen a slightly more speedy hull design.

Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for Wight Mk I 31 is 25%.

This ballast ratio shows a righting moment that is higher than 1% 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 Wight Mk I 31 is 308 which categorizes this boat among 'medium weight cruisers'.

27% 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.

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 21m² (226 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	9.3 m	(30.5 feet)	12 mm	(1/2 inch)
Genoa sheet	9.3 m	(30.5 feet)	12 mm	(1/2 inch)
Mainsheet	23.2 m	(76.3 feet)	12 mm	(1/2 inch)
Spinnaker sheet	20.5 m	(67.1 feet)	12 mm	(1/2 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 Wight Mk I 31 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.