The 2nd assistant engineer has just finished fueling operations. After entering the fuel data into the loading computer, you notice a greater than allowable at-sea bending stress. After the chief mate checks the voyage cargo data the vessel still has an excessive at-sea hogging bending stress. As chief engineer and after consulting with the chief mate, what should your instructions be to reduce the bending moment when ballasting the vessel?
• Hogging vs sagging bending moments — how weight distribution along the length affects them • Effect of adding weight at the ends versus adding weight at midships on the ship’s longitudinal strength • How ballast in forepeak, aftpeak, and midships tanks changes the bending stress curve
• Visualize the ship in hogging: are the ends or the middle more supported by buoyancy, and where is the structure most stressed? • Ask yourself: to counter a hogging moment, do you want to create more sagging or more hogging, and where should weight be added or removed to do that? • Compare what happens to the bending moment when you add ballast at the bow, at the stern, or at midships.
• Be clear on what hogging means: the ship is bent with the middle higher or lower than the ends? • Check which tanks (forepeak, aftpeak, amidships) are near the ends and which are near the center of the vessel’s length. • Confirm whether adding ballast at a location increases or decreases the bending moment at midships for a hogging condition.
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