Class 2 (2nd Engineer) SC&S 📅 Nov 2023

Exam Question

(a) Explain how trim occurs and explain the effect of trim on tank soundings. (6)

(b) A vessel of 8000 tonne displacement has 75 tonnes of cargo on the deck. It is lifted by a derrick whose head is 10.5m above the centre of gravity of the cargo and placed in the lower hold 9m below the deck and 14m forward of its original position. Calculate the shift in the vessel's centre of gravity from its original position when the cargo is (10)

(i) Just clear of the deck

(ii) At the derrick head

(iii) In its final position.

Reference Answer

(a) The effect of trim on tank soundings is significant because the reading obtained from the sounding pipe does not directly reflect the actual volume of liquid in the tank when the ship is trimmed. Typically, the sounding pipe is located at the aft end of the tank.
If the ship is trimmed by the stern , the liquid will settle more toward the aft end, resulting in a higher sounding than if the ship were on an even keel. Conversely, if the ship is trimmed by the bow , the liquid shifts forward, and the sounding obtained will be less , potentially underestimating the actual volume.
To ensure accurate volume measurement despite varying trim conditions, tank calibrations are carried out for different trims , and the data is compiled into a sounding book or trim correction table . When taking soundings, the trim is noted, and the corrected volume is obtained using these calibration tables , ensuring reliable tank content assessment regardless of trim.

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