Sailboat specifications and datasheets

Moody 31 MkI twin keel

The Moody 31 MkI, here in "twin keel" version, is a 30’8” monohull sailboat designed by Bill Dixon and Angus Primrose. She was built by Moody (United Kingdom) and made of GRP (glass reinforced polyester). This sailboat was produced between 1983 and 1985.

The Moody 31 MkI is as well listed, on, in version Fin keel.

Moody 31 MkI Moody 31 MkI layoutMoody 31 MkI sailingMoody 31 MkI accommodationsMoody 31 MkI accommodations
Moody 31 MkI's   Main Features
Model Moody 31 MkI
Version Twin keel
Type of hull Monohull
Category Cruising sailboat
Designer Bill Dixon
Angus Primrose
Construction GRP (glass reinforced polyester)
First built hull 1983
Last built hull 1985
Appendages Twin keel :
Fin without bulb
Helm 1 tiller (helm wheel in option)
Rudder 1 semi-spade rudder
Cockpit Closed aft cockpit
Unsinkable No
Trailerable No
Standard public price ex. VAT (indicative only) N/A
Moody 31 MkI's   Main dimensions
Hull length 30’ 8”
Waterline length 25’ 5”
Beam (width) 10’ 6”
Draft 3’ 8”
Light displacement 8752 lbs
Ballast weight 3675 lbs
Moody 31 MkI's   Rig and sails
Upwind sail area 558 sq.ft
Mainsail area 193 sq.ft
Genoa area 365 sq.ft
Jib area 215 sq.ft
Stormjib area 75 sq.ft
Rigging type Sloop Marconi masthead
Rotating spars No
Mast position Deck stepped mast
Spars Mast and boom in Aluminum
Standing rigging 1x19 strand wire continuous
Number of levels of spreaders 1
Spreaders angle 0 °
IiFore triangle height (from mast foot to fore stay attachment) 38’ 6”
JiFore triangle base (from mast foot to bottom of forestay) 12’ 6”
PiMainsail hoist measurement (from tack to head) 33’ 6”
EiMainsail foot measurement (from tack to clew) 11’ 6”
Moody 31 MkI's   Performances
Upwind sail area to displacementiThe ratio sail area to displacement is obtained by dividing the sail area by the boat's displaced volume to the power two-thirds.
The ratio sail area to displacement can be used to compare the relative sail plan of different sailboats no matter what their size. Upwind : under 18 the ratio indicates a cruise oriented sailboat with limited performances especially in light wind, while over 23 it indicates a fast sailboat.
Displacement-Length ratio (DLR)iThe Displacement Length ratio is a figure that points out the boat's weight compared to its waterline length. DLR is obtained by dividing the boat's displacement in tons by the cube of one one-hundredth of the waterline length (in feet).
The DLR can be used to compare the relative mass of different sailboats no matter what their length: a DLR less than 180 is indicative of a really light sailboat (race boat made for planning), while a DLR greater than 300 is indicative of a heavy cruising sailboat.
Ballast ratioiThe Ballast ratio is an indicator of the stability; it is obtained by dividing the boat's displacement by the weight of the ballast. Since the stability depends also of the hull shape and the position of the center of gravity, only boats with similar ballast arrangements and hull shape should be considered.
Higher the ballast ratio is, greater is the stability.
42 %
Hull speediAs a ship moves in the water, it creates standing waves that oppose its movement. This effect increases dramatically the resistance when the boat reaches a speed-length ratio (speed-length ratio is the ratio between the speed in knots and the square root of the waterline length in feet) of about 1.2 (corresponding to a Froude Number of 0.35) . This very sharp rise in resistance, between speed-length ratio of 1.2 to 1.5, is insurmountable for heavy sailboats and so becomes an apparent barrier. This leads to the concept of "hull speed".
The hull speed is obtained by multiplying the square root of the waterline length (in feet) by 1.34.
6.76 knots
Moody 31 MkI's   Auxiliary engine
Engine(s) 1
Engine type Inboard engine
Engine 28 HP
Fuel type Diesel
Fuel tank capacity 24 gal
Moody 31 MkI's   Accommodation
Cabin(s) 2
Berth(s) (min/max) 4 / 6
Head(s) 1
Fresh water tank capacity 35.9 gal

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