Question 14 TK01 - Tank Vessel Assistant - Dangerous Liquids

The Correct Answer is A. **Explanation for A ("get the bow up") being correct:** The primary concern when discharging an oil cargo, especially in rough seas or when nearing the completion of discharge, is maintaining the ship's stability and hull integrity by controlling stresses (shearing forces and bending moments) and ensuring efficient stripping (removing all remaining oil). By adopting a slight trim by the stern (getting the bow up), two critical objectives are achieved: 1. **Minimizing Sloshing and Structural Stress:** The ship’s main structure, the keel, is highly susceptible to hogging (bending moment where the middle dips lower than the ends) or sagging (bending moment where the middle bends upward). Discharging cargo often puts the ship through significant stress cycles. Maintaining a trim by the stern allows the discharge operations (the sequencing of tanks) to be managed in a way that keeps the structural stresses within safe limits. 2. **Efficient Stripping:** A trim by the stern is crucial for ensuring that the pumps can efficiently strip the remaining oil from the tanks. Gravity causes the oil to drain towards the stern end of the tanks (where the suctions are usually located), preventing large amounts of unpumpable residue (OBQ – On Board Quantity) from remaining, which is vital for commercial reasons and regulatory compliance (MARPOL). **Explanation of why other options are incorrect:** **B) discharge from amidships first:** While the sequence of tanks discharged is crucial for stress management, starting solely from the amidships tanks (the largest tanks and often the ones contributing most to bending moments) is usually *not* the first step. The overall stress management (keeping a safe trim/list) takes precedence over the specific starting location. In many common discharge plans, the process starts with a mix of center and wing tanks to control list and trim simultaneously, rather than exclusively amidships. **C) discharge from the centerline tanks first:** Centerline tanks are often the deepest and largest, and discharging them first helps reduce the draft quickly. However, discharging only centerline tanks dramatically increases the **metacentric height (GM)**, potentially leading to excessive stiffness and rapid, uncomfortable rolling (short roll period), which can induce high lateral stresses on the hull. Controlling stress and stability (which requires balancing center and wing tanks) must precede simply emptying the centerline tanks. **D) discharge from the wings first:** Discharging only the wing tanks first drastically reduces the metacentric height (GM) and may cause the ship to become tender (long roll period) or, worse, develop dangerously low stability (negative GM). This is highly dangerous and is almost never the correct procedure, as it risks capsizing or extreme listing. The sequence of wing and center tanks must be balanced to maintain adequate stability throughout the operation.