Review of Achilles 840

Basic specs.

sail specifications
The Achilles 840 is a sailboat designed by the maritime architect Chris Butler in the early eighties. The Achilles 840 is built by the British yard Butler Achilles Ltd.

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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 boat is equipped with 68.0 liter fresh water capacity.


The boat 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.


The Achilles 840 is equipped with a fin keel. A boat with a fin keel is more manoeuvrable but has less directional stability than a similar boat with a long keel.

The boat can enter most marinas as the draft is just about 1.52 - 1.62 meter (4.99 - 5.29 ft) dependent on the load. See immersion rate below.


Achilles 840 is typically equipped with an inboard Volvo Penta 2001 diesel engine at 9.0 hp (6 kW), which gives a max speed about 4.7 knots.

The fuel tank has a capacity of 98.0 liters (25 US gallons, 21 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 Achilles 840 is 2.04, 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 6.6 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 Achilles 840 is about 135 kg/cm, alternatively 759 lbs/inch.
Meaning: if you load 135 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 759 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 Achilles 840 is 17.9.

Low High 31% 0 50 100
Comparing this ratio with similar sailboats show that it is more comfortable than 31% of all similar sailboat designs. This comfort value is just below average.

L/B (Length Beam Ratio)

What is L/B (Length Beam Ratio)?

The l/b ratio for Achilles 840 is 3.09.

Wide Slim 54% 0 50 100
Compared with other similar sailboats it is slimmer than 54% 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 Achilles 840 is 45%.

Low High 73% 0 50 100
This ballast ratio shows a righting moment that is higher than 73% of all similar sailboat designs. A righting moment (ability to resist heeling) just above average.

D/L (Displacement Length Ratio)

What is Displacement Length Ratio?

The DL-ratio for Achilles 840 is 172 which categorizes this boat among 'light racers'.

Heavy Light 82% 0 50 100
82% of all similar sailboat designs are categorized as heavier. A light displacement requires less sailarea and has higher accellerations.

SA/D (Sail Area Displacement ratio)

What is SA/D (Sail Area Displacement ratio)?

The SA/D for Achilles 840 with ISO 8666 reference sail is 18.1, with a 135% genua the SA/D is 21.8.

Low High 76% 0 50 100
The SA/D ratio indicates that it is faster than 76% of all similar sailboat designs in light wind.

Over- / underrigged

Low High 73% 0 50 100
The Achilles 840 has more rig than 73% of all similar sailboats, which indicates that the boat is slightly overrigged.


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 24m2 (258 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.


Dimensions of sail for masthead rig.

mainsail specifications headsail specifications

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
Mainsail halyard 24.9 m(81.8 feet)8 mm(5/16 inch)
Jib/genoa halyard24.9 m(81.8 feet)8 mm(5/16 inch)
Spinnaker halyard24.9 m(81.8 feet)8 mm(5/16 inch)
Jib sheet 8.5 m(27.8 feet)10 mm(3/8 inch)
Genoa sheet8.5 m(27.8 feet)10 mm(3/8 inch)
Mainsheet 21.2 m(69.4 feet)10 mm(3/8 inch)
Spinnaker sheet18.6 m(61.1 feet)10 mm(3/8 inch)
Cunningham3.0 m(9.7 feet)8 mm(5/16 inch)
Kickingstrap5.9 m(19.5 feet)8 mm(5/16 inch)
Clew-outhaul5.9 m(19.5 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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