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Sailboat specifications and datasheets

Southerly 420

The Southerly 420 is a 42’2” monohull sailboat designed by Rob Humphreys. She was built by Northshore (United Kingdom) and made of monolithic bottom, sandwich sides and deck: fiberglass / vinylester vaccum bagged. This sailboat was produced between 2010 and 2017.

The Southerly 420 belongs to the Southerly range. The Southerly 420 has also been marketed as Southerly 435.

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Southerly 420's   Main Features
Model Southerly 420
Type of hull Monohull
Shipyard
Designer Rob Humphreys
Range Southerly
Construction Hull and deck:
monolithic bottom, sandwich sides and deck: fiberglass / vinylester vaccum bagged
First built hull 2010
Last built hull 2017
Appendages Keel (lifting) :
Swing keel
Helm 1 wheel
Rudder 2 spade rudders
Unsinkable No
Trailerable No
EC certification A
Standard public price ex. VAT (indicative only) N/A
Southerly 420's   Main dimensions
Hull length 42’ 2”
Waterline length 36’ 6”
Beam (width) 13’ 2”
Draft 8’ 11”
Draft when appendages up 2’ 10”
Mast height from DWL 61’ 6”
Light displacement 26015 lbs
Ballast weight 7782 lbs
Southerly 420's   Rig and sails
Upwind sail area 786 sq.ft
Downwind sail area 1206 sq.ft
Mainsail area 463 sq.ft
Jib area 323 sq.ft
Gennaker area 743 sq.ft
Rigging type Sloop Marconi 9/10
Rotating spars No
Mast position Deck stepped mast
Spars Mast and boom in Aluminum
Standing rigging 1x19 strand wire
Number of levels of spreaders 2
Spreaders angle Swept-back
Southerly 420'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.
14.08
Downwind 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.
21.61
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.
244
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.
30 %
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.
8.09 knots
Southerly 420's   Auxiliary engine
Engine(s) 1
Engine type Inboard engine
Engine 53 HP
Fuel type Diesel
Fuel tank capacity 76.1 gal
Southerly 420's   Accommodation
Cabin(s) 2
Berth(s) (min/max) 4 / 6
Head(s) 2
Fresh water tank capacity 144 gal

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