Question 1

Bending moment. c) Static force

Accepted Answer

Bending moment totals the shear along the hull; static force is the steady load behind it — still water plus waves set the stress. Shear force at each section sums weights against buoyancy along the length. Bending moment integrates that shear — hogging crests amidships, sagging troughs amidships. Static forces hold steady for the still-water curve; wave loading adds the dynamic margin class limits cap. Strength proved by section modulus, deflection watch and survey of hatch corners and strength deck. Surveyor follow-up: sagging swell ahead at load marks — hogging or sagging moment amidships, and what breaks first?

Question 2

Arrangements for panting

Accepted Answer

Panting is met with stiffness at the bow: deep web frames, panting beams and stringers tying the forepeak plating together. Panting is the contiguous bellowing in and out of shell plating under a varying wave pressure, worst in the forward region. Deep webs, panting beams and side stringers distribute the wave load and stop the plating working alone. Aforepeak tank and the fore-and-aft bulkhead add a flat panel that resists the flexing the plating wants to do. Thicker plate forward and heavier frames through the peak are the arrangement the surveyor looks for at the bow. Surveyor follow-up: forepeak plating oiled and dented with panting beams sound — is it the arrangement, the loading or the grounding?

Question 3

Panting pounding in detail

Accepted Answer

Panting is the plating breathing; pounding is the whole bow section being slammed by the sea — two different forebody problems. Panting: contiguous bellowing of the shell plating from the variable pressure of passing waves, worst in the forward region. Pounding: the bow structure as a whole being driven bodily by waves, throwing high local loads into the plating and frames. The forward draught is much less than amidships, so the local relative motion of water and plating is greatest there. Bottom strength in the forward third is worked harder for it, with closer floor spacing and heavier side shell plating. Surveyor follow-up: plating work-hardened at the forepeak with the draught fine forward — is it panting, pounding or grounding?

Question 4

Parametric pitching ya rolling (naam hi nhi sunna tha

Accepted Answer

Parametric rolling is the resonance the ship sets up for herself: the wave train matches her own period and she rolls far beyond the wave. It occurs when the encounter frequency of the wave train approaches the ship’s own natural rolling period, most often at reduced speed in a heavy sea. IMO considers it particularly dangerous when the wavelength is about 1.0 to 1.5 times the ship’s length. It is least on box-shaped vessels and full-form barges, because their fore and aft contours are not too dissimilar and little transverse interplay occurs. To reduce it, water ballast is used to alter the GMT and move the natural rolling period off the synchronous value, and an anti-rolling stabilising system is fitted. Surveyor follow-up: box container ship rolling hard in following sea at 8 knots — what has she hit, and what moves her off it?

Question 5

Sagging and hogging

Accepted Answer

Hogging bends the hull in a shallow curve with the ends down; sagging bends it the other way with the ends up. Hogging: the middle is supported and the ends droop — a wave crest amidships with the ship empty forward and aft. Sagging: the middle dips and the ends lift — a wave trough amidships, or a ship loaded heavily at the ends. A ship alternates between them with every wave, and the strength member that fights both is the torsion box. In the oral, name the loading condition as well as the shape — the condition is what the surveyor tests. Surveyor follow-up: hull found in the sagging condition at sea with a heavy bow trim — is that sea, trim or a grounding set?

Question 6

Torsion box, location

Accepted Answer

The torsion box runs fore and aft on the centreline in the deepest part of the ship, closed at the ends and open at the top. It is a closed rectangular box on the centreline, forming the keel girder from the fore end to the after end. It stiffens the hull against twisting, so that one end does not lag behind the other in a seaway. In double-bottom ships it sits in the centre tank or the duct keel, and the plating and structure close it in. It is the main longitudinal strength member — without it the hull is a beam with no spine. Surveyor follow-up: duct keel reported with no centreline plating at the after end — is it a torsion box or just a pipe tunnel?

Question 7

what is torsion box

Accepted Answer

A torsion box is a closed centreline structure that resists twisting: it is what stops a ship twisting like a rolled paper tube. A closed box girder on the centreline with high second moments of area about the horizontal and vertical axes. It carries the longitudinal bending as hogging or sagging and the twisting as torque, in one member. Without it the two ends of the hull would work independently and the ship would wring in a seaway. It is the difference between a ship and a barge with a box on each end — and the surveyor asks for it by name. Surveyor follow-up: hull with a centre girder but no top closure — is that a torsion box, and what is missing?

Torsion Box & Hull Strength — Most Asked Questions

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