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The Masthead
Know It All Contest Solution
to the March 2012 Question
on whether chainplate lugs as detailed allow for sufficient weld
to secure them.
The Know It All questions and correct answers are important design tips for students as well
as other marine professionals. We suggest that you file them away for future reference.
The Question Was:
The aluminum sloop
under construction at Flakey Bay
Boatbuilders. She has a conven-
tional aluminum mast with a double
spreader rig with double lowers and
no spreader sweepback. Flakey Bay
Boatbuilders needs you to confirm
that the weld on the combined inter-
mediate- and cap-shroud chain-
plates is sufficiently strong. The 3/4-
inch (19 mm) thick aluminum chain-
plate lug is welded to a 1/4” (6 mm)
knee under the deck, as shown in
the drawing. All is of 5086 alumi-
num. The intermediate shroud is
3/8” (9.52 mm) 1x19 316 stainless
rated at 14,500 lb. (6580 kg), and
the cap shroud cap shroud is 5/16”
dia. (8 mm) 1x19 316 stainless
rated at 10,300 lb. (4640 kg).
Do the chainplate lugs as detailed
allow for sufficient weld to secure
them against the loads from the two
shrouds they support?
CORRECTION: Above is exactly how
the question was presented; how-
ever, Alan Gilbert pointed out that
the description of the rig doesn’t
match the drawing. He’s correct (see
We Get Mail
, page 29). Happily, this
doesn’t change the validity of the
question itself or the answer.
The Winners Are:
Five correct answers were sent in for this question from naval architect and marine engineer Alan Gilbert; Westlawn stu-
dents Paul Thunberg and Less Allen; and Westlawn graduates Doug Frolich and Peter Banks. All are most definitely too
smart for their own good and have clearly demonstrated that special, ineffable combination of sagacity, perspicacity, and
unalloyed gumption required to be Know It Alls. Technically, under the contest rules, only the first three correct submis-
sions can be winners; however, in this case, the answers came in so closely bunched together that all five are winners. Gil-
bert and Allen are now two-time Know It Alls (heaven help them!). In recognition, of all our winners’ amazing demonstra-
tion of unmitigated brain power, Know It All certificates, Westlawn T-shirts and caps are on their way to each. All should,
henceforth, be addressed exclusively as, “Know It All.”
And the Solution Is:
The answer is no. These chainplates as detailed don’t allow for sufficient weld to hold the two shrouds they each support.
To check
’s chainplate welds, the first step is to find the design load for the chainplate attachment. This is
4/3rds (1.34 times) the breaking strength of the shroud, shrouds or stays attached to the chainplate.
Continued next page
June 2012 Page 25