Loading fertilizer at Paks with a developing list
Your 78 m × 9.4 m inland motor cargo vessel is loading 420 t of bagged fertilizer at Paks on the Danube. The holds are empty after discharge; tank-top loading limit is 3.5 t/m². You have two wing ballast tanks of 12 m³ each: port is 60% full, starboard is full. The bunker tank amidships is slack. After 260 t are loaded, the vessel lists 3° to port; freeboard to the port marks is 1.5 m. The loading plan shows a calculated GM of 0.42 m without free-surface correction. Wind is from the port beam at 12 m/s, and the berth is exposed to passing traffic. The next lock at Baja is 60 km downstream, with a forecast beam wind of 10–14 m/s. The loader is waiting for your decision. The stability booklet gives a minimum permissible GM of 0.35 m in the arrival condition and requires free surface to be included.
1. What does the 3° list and the stated GM tell you about the vessel's condition, and what immediate instruction do you give the loader?
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Stop loading immediately and do not allow the loader to resume. A 3° list is not merely cosmetic: with 260 t already loaded, the vessel has little remaining freeboard on the low side, and the stated GM of 0.42 m is uncorrected. The partly filled port wing tank and the slack bunker tank both create free surface, which reduces effective GM. Depending on tank breadths, the correction could easily be 0.10–0.15 m, leaving an effective GM close to or below the 0.35 m minimum. That is a stability warning, not a trim problem to be corrected by adding more weight high up. I would check all tank soundings, confirm the cargo distribution against the loading plan, inspect the hold for a shifted or wet bagged cargo, and calculate KG and free-surface correction before any further loading. If the list is caused by cargo, correct the cargo; if by ballast, correct the ballast. Do not assume the list is harmless because the GM figure is above the minimum before correction.
2. How do you correct the list without reducing stability further? Give a sequence and explain the risk of each action.
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Correct the list by removing free surface and lowering G, one tank at a time. The safest first choice is usually to press the partly filled low-side wing tank full, provided the increase in draft still leaves adequate freeboard and the tank is not damaged. Filling it completely adds weight low and on the low side and eliminates its free surface; a partly filled tank would make the free-surface problem worse. If filling the port tank would put the port side too deep or reduce freeboard below the permitted limit, empty it completely instead, then correct with cargo or another low ballast tank. Do not fill the high-side starboard tank to fight the list; that raises G and increases the risk when the wind comes onto the beam. The slack bunker tank should be either pressed full or emptied, not left slack. After each action, read the list and soundings, recalculate effective GM, and wait for the water to settle before the next step. A list should be corrected before loading resumes, not after departure.
3. The list is corrected to 0.5° and effective GM is 0.38 m. Do you sail to Baja in the forecast beam wind, and what operating limits do you set?
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With effective GM 0.38 m against a 0.35 m minimum, the margin is only 0.03 m. That is not enough to accept a 10–14 m/s beam wind on a high-sided vessel with 1.5 m freeboard and a lock approach at Baja. Wind heeling is dynamic and gusty, and the vessel would also be exposed on the reaches. I would not sail on the present loading and forecast. Options are to wait at the sheltered berth for the wind to ease, reduce the topside cargo or redistribute it lower if the cargo plan permits, or add low ballast if strength and freeboard allow and the stability calculation shows a useful increase in effective GM. If the decision is to proceed after improvement, I would set limits: no departure with effective GM below 0.35 m including free surface, keep list under 0.5°, press all ballast tanks, reduce speed in gusts, avoid the exposed reach, and abort to a safe berth if the list increases or steering becomes difficult. The schedule does not justify the risk.