Answer to Quiz No. 20


Question 1: The true angle is 60.55 degrees.

Question 2: The vertical height from hook to bottom of vessel is 21.44 feet.

Question 3: The tension in each leg of the sling is 57.42kips.

Question 4:

A 2” dia. IPS, IWRC, sling good for 60 kips could be used
OR
A 1 7/8” dia EIPS, IWRC, sling good for 64 kips could be used
COMMENTS:

As the section of each sling that is in contact with the shell follows an ellipsis, it is pretty complex to calculate the above answers. By making some assumptions, approximate answers can be obtained. It is left to the user to make a layout for the following steps.

1. The approximate distance H from the hook to the bottom of the vessel can be found by the following formula:

H = .5((20 feet Span/Tan (90-65))-10 feet Vessel OD) + 10 feet Vessel OD/2 = 21.45 feet.

2. Assume that the slings are tangent to the vessel at the horizontal centerline and then solve for the true angle using the H obtained above.

The approximate true angle is 60.99 degrees.

3. From the true angle, the approximate tension in each leg is 57.17 kips.

These answers are pretty close to the ones listed for the questions to the quiz because the slings are actually tangent to the shell 1.21 feet above the centerline of the vessel. If shorter slings or a larger diameter vessel had been used, the difference between the answers would be much greater as the assumption that the slings are tangent to the vessel at the centerline would be farther off. Of course, an original assumption could have been made that tangency was above the centerline some distance.

The answers listed for the questions in the quiz were obtained by a basket hitch program that can be found in the RIGGING DESIGN PROGRAMS section of this website. Just use the basket hitch program for a vessel without saddles.

      

    

    

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