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The Masthead
Know It All Contest Solution
Chainplate Design Load = 1.34 x shroud or stay breaking strength. This assumes a safety factor (SF) of 3 for the rigging
wire itself, which is standard and rec-
ommended. (Uppers may have an SF
of about 2.5) This is an SF of 4 over
the rigging loads (3.34 uppers.)
We have a 5/16” dia. (8 mm) 316
cap shroud and a 3/8” (9.52 mm)
stainless intermediate shroud. These
are both 1x19 316 stainless wire
rope. Breaking strengths are 10,300
lb. (4640 kg) and 14,500 lb. (6580
kg) respectively. Therefore:
Chainplate Design Load (CDL) =
(10,300 lb. + 14,500 lb.) x 1.34 =
33,232 lb.
Chainplate Design Load (CDL) =
(4640 kg + 6580 kg) x 1.34 = 15035
kgf = 147443
15035 kgf x 9.806 n/kgf = 147433 N
To avoid weld distortion, the heaviest
weld you should use in ordinary situa-
tions is 1/16th inch (1.5 mm) smaller
than the
plate being welded.
Thus if you have a 1/4-in. plate being
welded to a 3/8-in. plate, the heavi-
est weld would be 3/16 in.; or if you
have a 6 mm plate being welded to a
10 mm plate, the heaviest weld you
could use would be 4.5 mm. Lighter
weld causes less distortion, so you
want to use somewhat lighter welds
where possible, assuming that you
can get enough total weld length.
The chainplate design load (CDL) is 33,232 lb. or 147433 Newtons (N). Our aluminum chainplate 3/4 in. (19 mm) thick.
The aluminum knee it is being welded to is 1/4 in. (6 mm). This means that the heaviest weld usable is 3/16 in. or 4.5
mm. How many inches of 3/16-in. or 4.5 mm weld do you need to equal the required CDL?
Weld strength in lb. per lineal inch = WF x leg length, in. x cos 45° x psi
Weld strength in N per lineal mm = WF x leg length, mm x cos 45° x mPa
leg length = weld leg length, in. or mm
psi = shear strength of material in the as-welded condition (for aluminum this is shear strength in as-welded
mPa = shear strength of material in the as-welded condition (for alum. this is shear strength in as-welded yield)
WF = weld strength reduction factor = 0.75 for aluminum, 0.90 for bronze, 0.95 for steels
As-Welded Shear Strength
Marine Aluminum*
A36 Steel
A242 Cor-Ten
316 Stainless Steel
Silicon Bronze
*For aluminum as-welded YIELD shear
June 2012 Page 26
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