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Alphena One

2007

Alphena One is a 27′ 10″ / 8.5 m sailboat designed by Tanguy Le Bihan and built by Latitude 46 starting in 2007.

Designer
Tanguy Le Bihan
Builder
Latitude 46
Associations
?
# Built
?
Hull
?
Keel
Fin + Bulb
Rudder
Spade
Construction
GRP

Dimensions

Length Overall
27′ 10″ / 8.5 m
Waterline Length
25′ 5″ / 7.8 m
Beam
7′ 8″ / 2.4 m
Draft
5′ 2″ / 1.6 m
Displacement
3,970 lb / 1,800 kg
Ballast
1,320 lb / 600 kg (Lead)

Rig and Sails

Type
Fractional Sloop
Reported Sail Area
409′² / 38 m²
Total Sail Area
?
Mainsail
Sail Area
?
P
?
E
?
Air Draft
?
Foresail
Sail Area
?
I
?
J
?
Forestay Length
?

Auxilary Power

Make
Kraütler
Model
GPV 48 V electric motor
HP
0
Fuel Type
4x 12 V batteries
Fuel Capacity
?

Accomodations

Water Capacity
?
Holding Tank Capacity
?
Headroom
?
Cabins
?

Calculations

Hull Speed
9.7 kn
Classic: 6.76 kn

Hull Speed

The theoretical maximum speed that a displacement hull can move efficiently through the water is determined by it's waterline length and displacement. It may be unable to reach this speed if the boat is underpowered or heavily loaded, though it may exceed this speed given enough power. Read more.

Formula

Classic hull speed formula:

Hull Speed = 1.34 x √LWL

A more accurate formula devised by Dave Gerr in The Propeller Handbook replaces the Speed/Length ratio constant of 1.34 with a calculation based on the Displacement/Length ratio.

Max Speed/Length ratio = 8.26 ÷ Displacement/Length ratio.311
Hull Speed = Max Speed/Length ratio x √LWL

9.72 knots
Classic formula: 6.76 knots
Sail Area/Displacement
26.1
>20: high performance

Sail Area / Displacement Ratio

A measure of the power of the sails relative to the weight of the boat. The higher the number, the higher the performance, but the harder the boat will be to handle. This ratio is a "non-dimensional" value that facilitates comparisons between boats of different types and sizes. Read more.

Formula

SA/D = SA ÷ (D ÷ 64)2/3

  • SA: Sail area in square feet, derived by adding the mainsail area to 100% of the foretriangle area (the lateral area above the deck between the mast and the forestay).
  • D: Displacement in pounds.
26.11
<16: under powered
16-20: good performance
>20: high performance
Ballast/Displacement
33.3
<40: less stiff, less powerful

Ballast / Displacement Ratio

A measure of the stability of a boat's hull that suggests how well a monohull will stand up to its sails. The ballast displacement ratio indicates how much of the weight of a boat is placed for maximum stability against capsizing and is an indicator of stiffness and resistance to capsize.

Formula

Ballast / Displacement * 100

33.33
<40: less stiff, less powerful
>40: stiffer, more powerful
Displacement/Length
107.8
100-200: light

Displacement / Length Ratio

A measure of the weight of the boat relative to it's length at the waterline. The higher a boat’s D/L ratio, the more easily it will carry a load and the more comfortable its motion will be. The lower a boat's ratio is, the less power it takes to drive the boat to its nominal hull speed or beyond. Read more.

Formula

D/L = (D ÷ 2240) ÷ (0.01 x LWL)³

  • D: Displacement of the boat in pounds.
  • LWL: Waterline length in feet
107.77
<100: ultralight
100-200: light
200-300: moderate
300-400: heavy
>400: very heavy
Comfort Ratio
15.3
<20: lightweight racing boat

Comfort Ratio

This ratio assess how quickly and abruptly a boat’s hull reacts to waves in a significant seaway, these being the elements of a boat’s motion most likely to cause seasickness. Read more.

Formula

Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam1.33)

  • D: Displacement of the boat in pounds
  • LWL: Waterline length in feet
  • LOA: Length overall in feet
  • Beam: Width of boat at the widest point in feet
15.25
<20: lightweight racing boat
20-30: coastal cruiser
30-40: moderate bluewater cruising boat
40-50: heavy bluewater boat
>50: extremely heavy bluewater boat
Capsize Screening
2.0
<2.0: better suited for ocean passages

Capsize Screening Formula

This formula attempts to indicate whether a given boat might be too wide and light to readily right itself after being overturned in extreme conditions. Read more.

Formula

CSV = Beam ÷ ³√(D / 64)

  • Beam: Width of boat at the widest point in feet
  • D: Displacement of the boat in pounds
1.96
<2: better suited for ocean passages
>2: better suited for coastal cruising
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