Question 1

Shortly after departure in ballast, the vessel develops a persistent 5° list to starboard that does not respond to counter-ballasting. The list sometimes transfers to port. What is this condition?

Accepted Answer

ANGLE OF LOLL — RECOGNITION AND RESPONSE: The condition described — a list that changes sides, does not correct with counter-ballasting, and occurs in ballast condition — is an ANGLE OF LOLL. DEFINITION: An angle of loll occurs when the vessel's initial metacentric height (GM) is NEGATIVE or zero. The GZ curve dips below zero at small angles and crosses zero at a larger angle — this is the loll angle. The vessel is in a state of UNSTABLE EQUILIBRIUM at upright and will flop to one side at the loll angle. The roll from side to side is characteristic. CAUSE: excessive free surface effect reducing effective GM to zero or negative; loss of water-plane area (ice on deck, flooding); loading errors (cargo placed too high). CORRECT RESPONSE: (1) DO NOT COUNTER-BALLAST ON THE HIGH SIDE — this is the critical error. If the vessel is at angle of loll and you add ballast on the high (apparent upright) side, you increase displacement and the vessel may roll suddenly to the opposite loll angle, potentially capsizing; (2) CORRECT ACTION: ballast or transfer weight to the lowest point of the vessel. Fill the lowest available tanks (double bottom tanks) — this lowers the centre of gravity. The FSE will temporarily worsen but as the tanks approach full, the FSE reduces and GM recovers; (3) IDENTIFY CAUSE: why is GM negative? Excessive FSE from slack tanks? Check all tank levels. Cargo shifted? Load condition changed?; (4) MASTER: immediately inform master — this is a serious stability situation; (5) SLOW DOWN: reduce speed in heavy weather — wave action on a vessel with negative GM can rapidly lead to capsize. Angle of loll — the dangerous misdiagnosis: the most dangerous aspect of angle of loll is that it LOOKS like a list (asymmetric weight). If the officer identifies it as a simple list and rapidly counter-ballasts on the high side — the result can be catastrophic. Adding weight to the high side in a vessel with negative GM can cause a sudden violent roll to the opposite side (overcorrection) or complete capsize. This has caused maritime disasters. How to distinguish loll from list: LIST — the vessel is heeled due to an asymmetric weight. Roll characteristics: stable at the listed angle, returns to the same angle after disturbance. LOLL — the vessel is at the loll angle due to negative GM. Roll characteristics: lolls alternately to both sides; unstable around upright; "floppy" behaviour. The correct response: fill the double bottom (DB) tanks — they are the lowest tanks in the vessel. As DB tanks fill, the FSE temporarily increases (worsening the apparent condition), then as they approach full the FSE reduces and GM recovers. The worsening before improvement phase panics officers who don't understand the FSE geometry — they stop filling and try counter-ballasting. This is wrong. NEVER counter-ballast high-side in loll. Slow speed in heavy weather: a vessel with angle of loll has NEGATIVE initial stability. In heavy weather, a large wave could provide enough inclining moment to push the vessel past the stable angle. At zero or negative GM, capsize is possible from a wave alone.

Question 2

You are Chief Mate on a 25,000 GT general cargo vessel. During loading you have four partially filled ballast tanks. Explain the free surface effect and how you manage it.

Accepted Answer

FREE SURFACE EFFECT — CM MANAGEMENT: FREE SURFACE EFFECT (FSE): when a tank is partially filled (slack), the liquid surface is free to move. When the vessel heels, the liquid shifts to the low side, moving the centre of gravity to leeward. This effectively RAISES the metacentric height (reduces GM) by an amount called the Free Surface Correction (FSC). The correction formula: FSC = (i × ρ_liquid) / (V × ρ_vessel) where i = second moment of area of the liquid surface, V = displaced volume. Key points: (a) FSE depends on the WIDTH of the tank, not the depth of liquid. A wide tank with 50% fill has MORE FSE than a narrow tank completely full; (b) Two half-filled tanks have MORE FSE than one completely full tank of the same total volume; (c) The FSE is greatest at 50% fill — it reduces as the tank approaches full or empty. MANAGEMENT: (1) MINIMISE SLACK TANKS: fill tanks completely or keep them empty — avoid the 20-80% fill range if possible; (2) BALLASTING SEQUENCE: when ballasting, complete one tank before opening another; (3) LOADING COMPUTER: the loadicator calculates FSC for all slack tanks and applies it automatically to the effective GM display. NEVER rely on only the solid GM — use the effective GM (corrected for FSE); (4) CROSS-FLOODING PIPES: on tankers, cross-flooding allows rapid transfer — but creates additional FSE during the transfer period. Plan for this; (5) WHEN CARRYING GRAIN: FSM (Free Surface Moments) for grain are calculated in the grain loading manual — grain can shift like a liquid. The second moment of area (i): this is a geometric property of the liquid surface shape. For a rectangular tank, i = (l × b³)/12, where l is the length and b is the breadth. The b³ term means breadth is dominant — doubling the width increases FSE eightfold. This is why wide tanks are disproportionately dangerous when slack. The 50% fill maximum FSE: at 50% fill, the moment of inertia of the free surface is at maximum. As you approach full or empty, the surface area decreases and the FSE reduces. The practical rule "fill completely or empty completely" directly follows from this geometry. SOLAS IS Code (MSC.267(85)) — mandatory stability criteria: the International Stability Code 2008 mandates that stability is assessed using GM corrected for free surface effect (effective GM). Examiners want to see understanding that the loadicator's output of GM already includes the FSC — and that the CM must check effective GM, not solid GM. Grain: the IMO Grain Code (SOLAS VI/9) requires that grain cargo shifting moments and free surface moments are calculated and that the grain loading plan is prepared using the grain loading manual. Grain shifts like a liquid on heeling — the FSE analogy is exact. Ballast keel (option D): a ballast keel is a fixed weight on the keel that lowers the centre of gravity permanently. It does not compensate for dynamic FSE from slack tanks. No vessel relies on a ballast keel to manage FSE from operational slack tanks.

Question 3

In heavy weather, soundings reveal the port double bottom ballast tank is making water rapidly. List detected at 8° port. What is your immediate response as Chief Mate?

Accepted Answer

FLOODING — DOUBLE BOTTOM TANK — CM RESPONSE: (1) CALL MASTER IMMEDIATELY — flooding casualty — master must be informed; (2) STOP ANY CARGO OPERATIONS if ongoing; (3) ASSESS SOURCE: where is the water coming from? Bilge alarm on which tank? Is it seawater ingress (high chloride content) or cargo/freshwater (contaminated water)? Inspect access hatches, sounding pipes, filler caps — any open or damaged? Is the tank over-pressured (split plate)? (4) GENERAL EMERGENCY STATION: consider calling emergency stations for damage control readiness — crew must be ready to respond; (5) LIST CORRECTION: 8° is a significant and dangerous list. Options: (a) Counter-ballast on starboard side — ballast starboard double bottom tank(s) to counteract the list. This reduces freeboard on the low side and may be hazardous if the vessel is already tender; (b) Discharge port-side ballast — but if the flooding is through a hull breach, pumping out the flooded tank just adds more water; UNDERSTAND THE FLOODING TYPE FIRST: (c) If damage flooding through a crack — pumping cannot keep pace; focus on counteracting, not pumping; (6) DAMAGE STABILITY: use the vessel's Damage Stability Booklet (required for SOLAS vessels): identify the compartment; find the one-compartment or two-compartment survival criteria; check if the vessel can survive the flooding with adequate stability (GZ, range, residual GM); (7) SOLAS LIFEBOAT READINESS: if stability is marginal — prepare lifeboats and alert crew. Master will decide on distress signal; (8) MAYDAY READINESS: if vessel is in imminent danger — master transmits MAYDAY. Pumping flooded compartment (option B): this is a critical error. If the flooding is through a structural breach (hull crack, plating failure, fractured weld), the inflow rate may exceed any pump capacity. Pumping gives false confidence while the situation worsens. The correct action is: first, assess whether pumping can keep pace. If not — focus on damage control measures, list correction, and preparing for the worst case. 8° list dangers: at 8° list, the vessel's ability to take further listing is compromised. At this angle, waves from the low side have a shorter distance to reach the deck. Any additional free surface or flooding worsens the situation rapidly. In heavy weather with breaking seas, an 8° listed vessel is in serious danger. Counter-ballasting without assessment (option C): counter-ballasting immediately has two risks: (a) it increases total displacement, reducing freeboard; (b) if the flooding compartment is not isolated and is continuing to flood, adding water on the starboard side may correct the immediate list but does not stop the underlying problem. The Damage Stability Booklet: SOLAS II-1/8 requires passenger ships and cargo ships over 100m to carry damage stability information. The booklet lists the flooding survival criteria — typically one-compartment or two-compartment survival. The CM should know where the booklet is and understand how to apply it in an emergency. Chief engineer authority (option D): in an emergency, the CM does NOT wait for the chief engineer. The flooding may be in tank spaces (CM's domain) not machinery spaces. Emergency response is a team effort under the master's command.