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Know It All Contest Solution

continued

Accordingly we’d find:

3/16-in. weld = 0.1875 in.

0.75 WF x 0.1875 in. weld leg x cos 45° x 9,000 psi = 895 lb./lineal inch

33,323 lb. CDL

÷

895 lb./lineal inch = 37.23 in. long of 3/16-in. weld, use 38 inches

Or

0.75 WF x 4.5 mm weld leg x cos 45° x 62 mPa = 148 N/lineal mm

147433 N CDL

÷

148 N/lineal mm = 996 mm long of 4.5 mm weld, use 1 m

The chainplate as shown for the problem has a total of 8.3” + 3.8” + 8” of weld totaling 21.1”. This is insufficient

with the 3/16” weld and the weld attachment isn’t strong enough.

Or

The chainplate as shown for the problem has a total of 211 mm + 97 mm + 203 mm of weld, totaling 511 mm.

This is insufficient with the 4.5 mm weld and the weld attachment isn’t strong enough.

This is a very common problem and should be carefully reviewed during the design of any welded chainplate at-

tachment. In order to correct the problem, we need to add more weld and or thicker weld. We could make the

chainplate longer, but then it would project rather far into the boat, taking up valuable room.

The alternative is that

we can either change the knee the chainplate is being welded to 3/8” (9.5mm) thick or cut it out at the chainplate

area and weld in a 3/8” (9.5 mm) insert plate.

In that case the heaviest weld we can use becomes 5/16” (8 mm). This increases the weld strength as follows:

5/16” = 0.3125”

0.75 WF x 0. 3125 in. weld leg x cos 45° x 9,000 psi = 1,491 lb./lineal inch

33,323 lb. CDL

÷

1,491 lb./lineal inch = 22.34 in. long of 5/16-in. weld, use 23 inches

Or

0.75 WF x 8 mm weld leg x cos 45° x 62 mPa = 263 N/lineal mm

147433 N CDL

÷

263 N/lineal mm = 560 mm long of 8 mm weld

This is very close to the total weld need for attachment, but not quite. In order to get additional weld length we can

split the chainplate, making a fork in the bottom to work in more weld line. This works well as long as the split does

not project up into

the top 30% of the chainplate

‘

s underside at the deck and as long as all

corners are very well rounded to eliminate stress concentrations.

You can see the final configuration of the chainplate for adequate weld in the drawing

(previous page).

Total weld length is 8.3” + (2 x 4.1”) + 8”, or 24.5 in. — ideal. (Note that we haven’t

included the short welds around the small rounded ends and inside corner, which

does add a small bit more.)

Or

Total weld length is 211 mm + (2 x 104 mm) + 203 mm,

or 622 mm—ideal. (Note that we haven’t included the

short welds around the rounded ends and inside corner,

which does add a small bit more.)

June 2012 Page 27