Your vessel carries 45,000 tonnes of coal in a single-side-skin bulk carrier. As chief mate, describe the structural monitoring regime you maintain during the ocean passage to detect early signs of water ingress into cargo holds.

A. STRUCTURAL MONITORING DURING COAL PASSAGE — CHIEF MATE's REGIME: WHY COAL SPECIFICALLY: coal is a Group B cargo (may emit flammable gas) and some coals also contain moisture — bilge monitoring also relates to cargo safety, not just structural monitoring. STRUCTURAL MONITORING REGIME: (1) HOLD BILGE SOUNDINGS: take and record hold bilge soundings at defined intervals (every 4 hours is typical for coal voyages). Any unexpected rise in bilge level must be investigated immediately — distinguish rain water ingress (via hatch seals) from structural water ingress; (2) BALLAST TANK SOUNDINGS: compare ballast tank levels with sounding records — an unexpected rise could indicate cross-flooding through a cracked bulkhead; (3) VISUAL OBSERVATION: observe hold condition through inspection hatches if weather permits — look for surface water or wet spots on cargo; (4) WEATHER RECORD: log sea state and green water on deck — increased wave loading conditions require increased monitoring frequency; (5) HATCH COVER SEAL CHECK: after any heavy weather where green water came on deck — inspect hatch seals for damage; (6) STABILITY MONITORING: any unplanned weight increase in the hold will affect stability — check GM calculation. SOLAS XII REQUIREMENT: large single-side-skin bulk carriers are required to have water ingress detection systems in cargo holds and ballast tanks with audible and visual alarms on the bridge.

B. Bilge monitoring during an ocean passage is the duty engineer's responsibility. The chief mate's monitoring responsibilities are in port only.

C. Take bilge soundings once daily at noon. Additional monitoring is only required if the bilge alarm activates — alarms are the primary monitoring system.

D. Structural monitoring during a coal passage is unnecessary as coal is a solid cargo. Water ingress monitoring only applies to liquid cargo on bulk carriers.

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.