Detailed sailboat specifications and datasheets since 2015
Imperial & Metricboth
Moody 31 MkI Twin keel
Last update: 24th March 2020
The Moody 31 MkI is a 30’8” (9.37m) cruising sailboat designed by Dixon Yacht Design (United Kingdom) and Angus Primrose (United Kingdom). She was built between 1983 and 1985 by Moody (United Kingdom). The Twin keel version allows a shoal draft and stability while beaching.
iFore triangle height (from mast foot to fore stay top attachment)
38’ 6”11.73 m
iFore triangle base (from mast foot to bottom of forestay)
12’ 6”3.81 m
iMainsail hoist measurement (from tack to head)
33’ 6”10.21 m
iMainsail foot measurement (from tack to clew)
11’ 6”3.51 m
Sloop Marconi masthead
Deck stepped mast
Number of levels of spreaders
1x19 strand wire continuous
Moody 31 MkI's performances
Upwind sail area to displacement
iThe 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 25 it indicates a fast sailboat.
222 ft²/T20.66 m²/T
Displacement-length ratio (DLR)
iThe Displacement Length Ratio (DLR) is a figure that points out the boat's weight compared to its waterline length. The 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.
iThe Ballast ratio is an indicator of stability; it is obtained by dividing the boat's displacement by the mass of the ballast. Since the stability depends also of the hull shapes and the position of the center of gravity, only the boats with similar ballast arrangements and hull shapes should be compared.
The higher the ballast ratio is, the greater is the stability.
Critical hull speed
iAs 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.