Downloadable Sailboat Plans by George Whisstock

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Unstayed Masts (Page 8)

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Properties of Common Materials
Material	R = Modulus of Rupture in N/mm^2	E = Modulus of Elasticity in N/mm^2	W = Weight (density) in kg/m^3
Douglas Fir¹	69 N/mm^2	13400 N/mm^2	480 kg/m^3
Aluminium Alloy	255 N/mm^2 (0.2% Yield Point)	69000 N/mm^2	2700 kg/m^3
Carbon Fibre²	570 N/mm^2 (UCS)	70000 N/mm^2	1580 kg/m^3
¹Average for clean Douglas Fir (straight grain, no knots), moisture content ≤ 12%. ²Figures are for an average carbon fibre/resin lay-up. May vary considerably by sparmaker or tube supplier.
This calculator is for circular unstayed masts; not for other shapes or for stayed masts.

Name of vessel:
In the following fields enter positive numbers only, without commas or spaces; decimal point is OK. Be sure to get your units right! N = newtons; kg = kilograms; m = metres; mm = millimetres. The calculator assumes a parallel section of mast from heel to a point beyond the partners (usually the gooseneck or boom height) and then an optional taper from there to the head.
Entered Values: All values must be entered, otherwise you will get an error!
Enter Displacement in kg		kg
Enter GZ at 30º in m		m
Enter maximum GZ in m		m
Enter L = length from CE to Partner in m		m
Enter R = Modulus of Rupture in N/mm^2		N/mm^2
Enter E = Modulus of Elasticity in N/mm^2		N/mm^2
Enter W = Density in kg/m^3		kg/m^3
Enter D = Outside Diameter of spar at partners in mm		mm
Enter T = Wall Thickness of spar at partners in mm		mm
Enter H = Length of parallel section in m		m
Enter H1 = Length of tapered section in m		m
Enter D1 = Outside diameter at head in mm		mm
Enter T1 = Wall Thickness at head in mm		mm
Calculated Results:
d = Inside Diameter of spar at partner		mm
d1 = Inside Diameter of spar at head		mm
RM30 = Righting Moment at 30º		Nm
RMmax = Max. Righting Moment		Nm
F30 = Force at 30º		N
Fmax = Max. Force		N
y = Distance from extreme to Neutral Axis		mm
I = Moment of Inertia		mm^4
Z = Modulus of Section		mm^3
S30 = Stress in spar at 30º		N/mm^2
Y30 = Deflection of spar at CE at 30º		mm
sf30 = Safety Factor at 30º
Smax = Max. Stress in spar		N/mm^2
Ymax = Max. Deflection of spar at CE		mm
sfmax = Safety Factor at Max. Stress
A = Area at partners		mm^2
a = Area at head		mm^2
M = Weight of whole mast		kg

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© George Whisstock. This article is for information only and may not be commercially reproduced in any form or used in any way without permission. Do not use this material as the basis for designing a mast without professional advice.