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Review of Commander 31


Commander 31
Commander 31 anno 1970.


Basic specs.

sail specifications
The Commander 31 is a sailboat designed by the maritime architect Knud E. Hansen together with Jan Kjærulff from Denmark in the late sixties. A few hundred boats have been produced. The Commander 31 is built by the Danish yard Bianca Yacht I/S.

Looking for a new boat? Find a Commander 31 or similar boat for sale

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.
The hull is a double hull which improves the indoor climate. Especially when the water is colder than the air in the cabin, then the double hull insulates against cold water and reduce the condense water in the cabin.

Interior
Interior
Interior of Commander 31 anno 1971.
The interior is like many other boats made of mahogany.
The boat is equipped with 6 berths, a galley and toilet facility.
Front cabin
Front cabin of Commander 31 anno 19971.
Galley
Galley of Commander 31 anno 1969.

Cockpit
Cockpit
Cockpit of Commander 31 anno 1971.
Rig
The boat has multiple rigs.

One option is 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.

Another option is 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
Keel
Keel of Commander 31 anno 1970.

The Commander 31 is equipped with a fin keel. The fin keel is the most common keel and provides splendid manoeuvrability. The downside is that it has less directional stability than a long keel.

Commander 31 can enter most marinas as the draft is just about 1.66 - 1.76 meter (5.45 - 5.75 ft) dependent on the load. See immersion rate below.


Engine

The boat is typically equipped with an inboard Volvo Penta MD1B diesel engine at 10.0 hp (7 kW), which gives a max speed about 4.0 knots.

The transmission is a shaft drive. A shaft drive will in the long run require less maintenence than other types of drive e.g. a sail drive.


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 Commander 31 is 1.78, 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 6.3 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 Commander 31 is about 120 kg/cm, alternatively 673 lbs/inch.
Meaning: if you load 120 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 673 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 Commander 31 is 26.6.

Low High 66% 0 50 100
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 Commander 31 is 3.50.

Wide Slim 82% 0 50 100
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.


Ballast Ratio

What is a Ballast Ratio?

The ballast ratio for Commander 31 is 46%.

Low High 76% 0 50 100
This ballast ratio shows a righting moment that is higher than 76% 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 Commander 31 is 324 which categorizes this boat among 'medium weight cruisers'.

Heavy Light 21% 0 50 100
21% 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.


RSP (Relative Speed Performance)

What is Relative Speed Performance?

The Relative Speed Performance for Commander 31 is 46

Slow Fast 46% 0 50 100
The relative speed performance is 46 which means that a it is faster than 46% of all similar sailboat designs.


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 22m2 (236 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
Masthead rig
UsageLengthDiameter
Jib sheet 9.4 m(30.8 feet)12 mm(1/2 inch)
Genoa sheet9.4 m(30.8 feet)12 mm(1/2 inch)
Mainsheet 23.5 m(76.9 feet)12 mm(1/2 inch)
Spinnaker sheet20.6 m(67.7 feet)12 mm(1/2 inch)
Fractional rig
UsageLengthDiameter
Jib sheet 9.4 m(30.8 feet)12 mm(1/2 inch)
Genoa sheet9.4 m(30.8 feet)12 mm(1/2 inch)
Mainsheet 23.5 m(76.9 feet)12 mm(1/2 inch)
Spinnaker sheet20.6 m(67.7 feet)12 mm(1/2 inch)
Fractional rig
UsageLengthDiameter
Jib sheet 9.4 m(30.8 feet)12 mm(1/2 inch)
Genoa sheet9.4 m(30.8 feet)12 mm(1/2 inch)
Mainsheet 23.5 m(76.9 feet)12 mm(1/2 inch)
Spinnaker sheet20.6 m(67.7 feet)12 mm(1/2 inch)

Boat owner's ideas

This section shown boat owner's changes, improvements, etc. Here you might find inspiration for your boat.

Do you have changes/improvements you would like to share? Upload a photo and describe what to look for.



Finally

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