With reference to stresses and strain in vessels, describe, with the aid of a sketch, EACH of the following: (a) panting;(2) (b) pounding;(2) (c) racking;(2) (d) hogging;(2) (e) sagging;(2)
(a) Panting (2 marks)
Panting is the in-and-out flexing (“breathing”) of the bow plating caused by cyclic variations in water pressure as the vessel pitches in heavy seas.
It occurs mainly in the forward parts of the hull near the bow, where wave pressure alternately increases and decreases as the ship meets head seas.
(b) Pounding (2 marks)
Pounding is the slamming impact of the ship’s forefoot or bottom plating onto the sea surface when the vessel lifts clear on a wave crest and falls heavily into a trough.
It produces severe shock loads and vibration on the bottom shell plating, forepeak floors, and framing.
(c) Racking (2 marks)
Racking is the transverse distortion of the hull structure due to side-to-side movement when rolling in a seaway.
The ship’s rectangular cross-section tends to deform into a parallelogram, placing shear stress on the side frames, deck beams, and bulkheads.
(d) Hogging (2 marks)
Hogging occurs when the vessel’s midship region is supported by a wave crest while the bow and stern are unsupported in troughs.
The hull bends upward amidships, placing the deck in tension and the bottom in compression.
(e) Sagging (2 marks)
Sagging occurs when the bow and stern are supported by wave crests while the midship region is in a trough.
The hull bends downward amidships, placing the deck in compression and the bottom in tension.
