Junk Rig Calculation Tools

Work in progress, send comments and/or suggestions here

Jump to: Mass/strength Angle/rake Hull Sail

Spar mass/strength

Calculates the mass and breaking strength of a solid or hollow spar

Straight Tapered Solid Hollow

Input:

Length m
Base diameter mm
Top diameter mm
Thickness mm
Material aluminum, density 2.7 steel, density 7.85 wood (Cedar, western red), density 0.38, modulus of rupture 52 MPa wood (Spruce, Norwegian), density 0.43, modulus of rupture 72 MPa wood (Douglas fir or Pine), density 0.53, modulus of rupture 87 MPa wood (Oak), density 0.75, modulus of rupture 96 MPa UHMWPE (PE 1000), density 0.93, modulus of rupture 30 MPa Carbon fiber, density 1.55, ultimate tensile strength 1700 MPa

Results:

Mass kg
Breaking strength kpm

Densities from http://www.engineeringtoolbox.com/material-properties-t_24.html
Modulus of rupture from http://www.conradfp.com/pdf/ch4-Mechanical-Properties-of-Wood.pdf (mirror)
UHMWPE (PE 1000): http://www.arpnjournals.org/jeas/research_papers/rp_2019/jeas_0719_7819.pdf and https://www.azom.com/properties.aspx?ArticleID=909 Carbon fiber calculation is experimental

Spar angle/rake

Calculates spar angles (mast rake for example)

Solve for: Angle Distance Length

Fill in the two missing factors and remember to use the same unit for length and distance

Example 1: If you want to find out how much forward the top of a 9 meter mast is compared to the base with 4 degree rake, choose "Distance" and fill in "9" for length and "4" for angle.

Example 2: If you want to find out how rake there is on a 12 meter mast which top is 1.02 meters forward of the base, choose "Angle" and fill in "12" for length and "1.02" for distance.

Input:

Spar length m
Spar distance m
Spar angle degrees

Credit goes to http://www.1728.org/angsize.htm

Hull properties

Calculates sail area vs. displacement and displacement vs. waterline ratios

Input:

LWL m
Displacement kg
Beam m
Sail area m²

Results:

Disp/LWL ratio
SA/Disp ratio
Hull speed knots
Righting moment kpm

SA/disp

• 10-14 Cruising sailboat
• 15-19 Cruiser-racer
• 20-24 Racing sailboats
• 25+ High-Performance racers

Disp/LWL

• 0-49 Ultralight
• 50-119 Very light
• 120-249 Light
• 250-319 Medium
• 320-379 Heavy
• 380+ Very heavy

Sail properties

Calculates batten lengthts for given sail area

Input:

Sail design David Tyler (Fantail-type) Arne Kverneland (Johanna-type)
Sail area m²

Results:

Yard m
Batten 1 m
Batten 2 m
Batten 3 m
Batten 4 m
Batten 5 m
Batten 6 m
Batten 7 m
Boom m
Mast LAP m (recommended minimum)
Mast LOA m (minimum)

Fantail calculations from https://junkrigassociation.org/technical_forum/1060993

Johanna calculations based on http://www.junkrigassociation.org/Resources/Documents/Arne%20Kverneland's%20files/Johanna's%20sail%20plan,%20sheet%201-9.pdf