Class 2 (2nd Engineer) SC&S 📅 Feb 2024

Exam Question

(a) Explain the concept of dynamical stability. (6)

(b) A vessel of 8000 tonne displacement has 75 tonne 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) Dynamical Stability is defined as the amount of energy required to heel a ship from its upright equilibrium position to a specific angle of heel. It provides a measure of the vessel's stability by considering its behaviour in response to dynamic external forces , such as wind or waves.
The concept compares the heeling moment energy (from external forces) and the righting moment energy (from the ship's stability).
The ship will absorb the energy imparted by the heeling moment. If the righting energy is greater than the heeling energy, the ship will stabilize; otherwise, it may capsize.
Areas Under the Curve:

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