Aux 2 Unit 16 Stress on hull Q3 Answer

  1. (a) Explain what is meant by the term pounding as applied to a vessel being driven hard in a seaway.(3)
    (b) Explain how panting may often occur at the same time as pounding in heavy seas.(3)
    (c) Describe how the hull is strengthened to resist panting and pounding.(4)

(a) Meaning of the Term Pounding (3 marks)

  • Pounding is the slamming or heavy impact of the ship’s forepart (bow) onto the sea surface when the vessel is driven hard in a seaway, particularly in head seas.
  • It occurs when the vessel’s bow lifts clear of the water on a wave crest and then falls heavily onto the next wave trough, causing repeated shock loads on the forward bottom plating and structure.
  • These impacts cause vibration, noise, and high local stresses in the forefoot, bottom shell, and forward framing of the hull.

(Clear definition + where and why it occurs + effect = 3 marks)

(b) How Panting May Occur at the Same Time as Pounding (3 marks)

  • Panting is the in-and-out flexing (breathing) of the bow plating due to changes in water pressure as the vessel pitches in heavy seas.
  • When the ship drives into oncoming seas, water pressure increases sharply on the bow plating; as the bow rises out of the water, the pressure drops.
  • This alternating pressure causes the bow plating to “pant” (vibrate in and out).
  • During pounding, the sudden impact loads at the forefoot coincide with these pressure fluctuations, so panting and pounding often occur together, subjecting the bow to severe cyclic stresses.

(Explanation of panting, how it relates to pressure variation, and simultaneous occurrence with pounding = 3 marks)

(c) Strengthening to Resist Panting and Pounding (4 marks)

To Resist Pounding:

  1. Increased plate thickness in the bottom shell, forefoot, and bilge areas.
    • Provides greater rigidity and resistance to impact forces.
  2. Additional bottom floors and intercostal girders in the forward bottom structure.
    • Distribute shock loads from slamming over a wider area and reduce local stress.

To Resist Panting:

  1. Panting stringers (horizontal stiffening girders) fitted inside the bow between the stem and first watertight bulkhead.
    • Support the side shell plating against in-and-out movement.
  2. Panting beams and brackets connecting the frames and stringers.
    • Tie the plating to the internal framing and reduce vibration and distortion.

(2 marks for pounding strengthening, 2 marks for panting strengthening = 4 marks)