You are chief mate loading steel billets. The loading plan shows the stowage weight on hatch cover No. 2 will be 85 tonnes distributed over the panel. The hatch cover certificate shows a maximum distributed load of 1.75 T/m² and the panel area is 42 square metres. Confirm whether this is acceptable.

A. HATCH COVER LOAD ASSESSMENT — CALCULATION: STEP 1 — CALCULATE MAXIMUM PERMITTED LOAD: Panel area = 42 m². Maximum distributed load = 1.75 T/m². Maximum load = 42 × 1.75 = 73.5 tonnes total. STEP 2 — COMPARE WITH PROPOSED LOAD: Proposed load = 85 tonnes. 85 tonnes > 73.5 tonnes maximum. THE LOAD EXCEEDS THE HATCH COVER MAXIMUM. ACTION: (1) The proposed stowage of 85 tonnes on hatch No. 2 cover is NOT acceptable and must be revised; (2) Reduce weight on this cover to maximum 73 tonnes (with a working margin below the 73.5 limit); (3) Alternatively: distribute some steel billets to deck stowage elsewhere or to a hold; (4) Inform the terminal / chief mate's counter-check on the loading plan must be completed before cargo commences; (5) Document the revised loading plan. NOTE ON POINT LOADS: even if total distributed weight was acceptable, steel billets may create point loads at their contact points with the hatch cover — check whether the certificate also specifies a point load limit and whether packing/dunnage is required to distribute the load.

B. The load is acceptable. The certificate limit of 1.75 T/m² is a conservative design figure with a safety factor of 2.5 built in — actual failure load is approximately 4.4 T/m², so 85 tonnes is well within the real structural limit.

C. The loading computer will automatically prevent loading if the hatch cover is overloaded. The chief mate does not need to manually cross-check hatch cover loads against the certificate.

D. The calculation shows 73.5 tonnes is the limit but this is a design figure in calm conditions. At sea with pitch and roll, dynamic loads may reduce the effective limit — only load to 60% of the design figure.

A. BENDING MOMENT AND SHEAR FORCE — CONCEPTS AND ACTION: BENDING MOMENT (BM): the internal moment within the ship's hull that resists the tendency of the vessel to "hog" (bend upwards at the centre when supported at ends) or "sag" (bend downwards at the centre when buoyancy exceeds weight amidships). BM is measured in tonne-metres and varies along the ship's length. SHEAR FORCE (SF): the internal vertical force within the hull at any cross-section — the tendency of the ship to "shear" (vertical displacement between adjacent sections). Caused by unequal distribution of weight and buoyancy. STILL WATER vs WAVE BM: still water BM is calculated at the loading port and is the controllable component. Wave BM is added at sea and is the classification society's additional allowance. MAXIMUM PERMISSIBLE STILL WATER BM: the value stated in the ship's loading manual is the maximum still water BM that the vessel's structure can withstand in still water, with a reserve for wave-induced BM at sea. EXCEEDING THE LIMIT: the proposed sequence results in 9,100 vs maximum 8,500 tonne-metres — this is 7% over the permissible limit. THE VESSEL MUST NOT SAIL in this condition. ACTION REQUIRED: (1) Modify the loading sequence — redistribute cargo between holds; (2) Add ballast to alter buoyancy distribution; (3) Reduce total cargo weight; (4) Recalculate until within limits; (5) Document the revised plan and recheck BM and SF on the loading computer.

B. The maximum permissible value is a conservative limit with a 10% tolerance built in. A bending moment 7% over the stated limit is within the safety margin and the vessel may sail.

C. Shear force and bending moment limits only apply in port loading operations. At sea, wave action overrides the still water values and the loading computer limits are not relevant.

D. Contact the classification society for a dispensation to sail over the limit. Classification societies routinely grant dispensations for temporary bending moment exceedances at loading ports.

A. HOGGING AND SAGGING — DEFINITIONS AND CAUSES: SAGGING: the vessel bends so that the midship section is lower than the bow and stern — the hull curves downward like a banana shape with the centre lowest. CAUSES: (a) Heavy cargo concentrated amidships with relatively empty ends — weight exceeds buoyancy amidships; (b) At sea: when the vessel is in the trough of a wave — buoyancy is reduced amidships (both bow and stern supported by wave crests). STRESS IN SAGGING: the keel and bottom structure are in TENSION; the deck structure is in COMPRESSION. HOGGING: the vessel bends so that the midship section is higher than the bow and stern. CAUSES: (a) Heavy cargo at the ends with a light or empty midships section; (b) At sea: when the vessel is at the crest of a wave — midships is supported by the wave while bow and stern overhang the troughs. STRESS IN HOGGING: the deck is in TENSION; the keel is in COMPRESSION. PRACTICAL SIGNIFICANCE: most bulk carriers are more vulnerable to hogging in heavy weather (empty holds or light cargo at midships with heavy ore at ends). Structural failures have occurred from excessive hogging loads in severe weather. LOADING TO BALANCE: a well-loaded bulk carrier distributes heavy cargo to minimise both sagging and hogging BM — check the loading computer output for the BM envelope diagram.

B. Sagging occurs when the bow is heavily loaded and the stern is light. Hogging occurs when the stern is heavily loaded and the bow is light.

C. Hogging and sagging refer to the list of the vessel, not bending. A hogged vessel lists to port, a sagged vessel lists to starboard.

D. Sagging is when the vessel is heavy overall and riding low in the water. Hogging is when the vessel is light and riding high. Both are stability terms, not structural terms.