List Alternating Between Port and Starboard After a Ballast Transfer
MV Iron Meridian is a 76,000 t deadweight Panamax bulk carrier of 32.2 m beam, sailed from a river berth with a full grain cargo and a departure GM of 0.28 m. Two hours out in open water the ship takes a steady 8° list to port. The chief engineer reports that No. 3 port double-bottom ballast is sounding 0.7 m below the declared figure - the tank was left slack and its suction was never tested. The master orders No. 3 port pumped out and No. 3 starboard filled; the list eases to 4° to port, then, on a 20° course alteration, the ship rolls slowly through 10° to starboard and settles at 9° to starboard with an easy, long roll. The weather is a 2 m swell. Freeboard to the deck edge on the low side is 1.9 m. The grain stability booklet shows a heeling angle of 10° for a 15° shift of grain.
1. Diagnose the condition: is this a list or an angle of loll? Give the evidence and explain its significance.
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The evidence points to loll, not list. A true list is a stable equilibrium: the centre of gravity is off the centreline, the ship has positive GM, and a small course or heel disturbance produces a restoring moment back to the same angle. Here the ship did the opposite. It departed with GM 0.28 m, already marginal; a slack tank added free surface and raised the effective KG; and transferring ballast from the low side to the high side added weight high and removed weight low, pushing GM negative. Once GM is negative the upright position is unstable, and the ship settles at the angle where GZ returns to zero - the angle of loll - with a small positive slope at that angle. The slow roll from 10° to starboard and the easy, long roll are the classic signature: the ship is hunting between two equilibrium angles.
Why it matters. A loll is not cosmetic. There is no righting moment at small angles, so the vessel has no reserve to absorb a swell or a rudder-induced heel, and the tank free surface is still active. The report of 1.9 m freeboard at 9° is misleading: at half-beam 16.1 m, a 9° heel lifts the deck edge by 16.1 × sin 9° = 2.52 m, which exceeds the freeboard. The deck edge is already immersed, so the intact-stability criterion of no deck-edge immersion is breached, down-flooding through air pipes and hatch openings becomes credible, and the 10° grain heeling moment could take the ship past the point of no return.
2. State the corrective action sequence, with the reasoning for each step and the traps to avoid.
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Step 1 - stop and secure. Stop all ballast transfers and close every watertight and weathertight opening, air pipe and sounding cock on the low side. Reduce speed and steer a course that keeps the swell fine on the bow to minimise rolling. No one goes on the low-side deck. Muster the crew, brief them, and have lifejackets ready.
Step 2 - kill the free surface. Press up the slack No. 3 port tank and any other part-filled tank fully, one tank at a time. A pressed tank contributes no free surface; a slack one does. This alone can restore a small positive GM.
Step 3 - lower G using low weight. Fill the lowest double-bottom tanks, working on the low side and centre tanks first, again one at a time and pressed full. This is the step that actually removes the loll; filling high tanks or transferring from the low side to the high side - the error already made - adds heeling moment and can flip the ship from one loll to the other, which is what happened here.
Step 4 - watch for the crossover. As GM becomes positive the ship should rise through the loll angle and come upright. If it comes upright and then takes a list to the opposite side, stop, do not chase it with more ballast, and recalculate from the new soundings.
Traps. Do not use large rudder angles or the engine to "roll it upright"; do not assume soundings match the plan - sound every tank; do not press up a tank on the high side first.
3. State the verification, reporting and documentation you would require before the ship resumes passage.
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Verification. Re-sound every tank, recompute KG, GM and the GZ curve on the loading computer and check against full IMO intact stability criteria: initial GM at least 0.15 m, area under the GZ curve to 30° at least 0.055 m·rad, GZ at least 0.20 m at 30°, maximum GZ at not less than 30°, area to 40° at least 0.09 m·rad, and freeboard consistent with no deck-edge immersion. Then apply the grain criteria separately: the heeling angle from a 15° shift of grain must not exceed 12° or the angle of flooding, whichever is less, and the residual area must be positive.
Reporting. Inform the company/DPA immediately, with the sequence of events, the actions taken and the computed condition; request a naval architect's or class review of the loading computer result before the ship proceeds at full speed; and consider a port of refuge if the swell is forecast to build or if the deck edge remains close to the water.
Documentation. Soundings before and after each transfer, times and quantities, the ballast plan and who authorised it, the departure stability calculation and the free-surface allowances used, photographs of the low-side deck edge, and statements from the chief officer and chief engineer. The slack tank and untested suction are an ISM non-conformity and must be raised through the non-conformity process, not quietly corrected.