Question 1

Your vessel is loading a 150-tonne heavy lift cargo using the vessel's crane. As Master, what stability and safety precautions must be observed?

Accepted Answer

HEAVY LIFT — STABILITY AND SAFETY PRECAUTIONS: STABILITY DURING CRANE OPERATIONS: when a weight is suspended from a crane — the EFFECTIVE CENTRE OF GRAVITY of that weight rises to the CRANE HEAD (the hook). This is because the suspended weight can swing freely and behaves as if its entire mass is at the point of suspension. FOR A 150-TONNE SUSPENDED LIFT: (1) SUSPENDED WEIGHT EFFECT: 150 tonnes at the crane head. If the crane head is 20m above the keel (KG): the 150 tonnes acts at 20m, not at the stowage position (e.g., 2m). This creates a significant virtual rise in G; (2) PRE-LIFT STABILITY CALCULATION: the stability calculation must be run with the weight at the crane head height. If this results in reduced GM or approach to a stability limit — correct BEFORE the lift; (3) BALLAST COMPENSATION: ballasting down (adding low ballast to double bottom tanks) before the lift compensates for the virtual rise in G from the suspended weight; (4) CRANE HEEL: the crane working over the side introduces a heeling moment. The vessel must have adequate GM to resist the heel angle from the crane offset; SAFETY PRECAUTIONS — ISM AND COSWP: (1) PERMIT TO WORK: heavy lift operation requires a documented PTW; (2) RISK ASSESSMENT: the lifting plan must include risk assessment covering: wind speed limits, crane load limits, tagline control, exclusion zones; (3) MARINE SURVEYOR: independent marine surveyor typically attends to certify the lift plan and verify sling arrangements; (4) CRANE CERTIFICATES: the crane Safe Working Load (SWL) must exceed the 150-tonne lift weight with appropriate safety factor; (5) WEATHER LIMITS: wind speed limit for the operation (typically Beaufort 3-4 for offshore lifts); (6) PERSONNEL: all non-essential crew away from the working area (exclusion zone); (7) EMERGENCY PLAN: what happens if the crane fails during the lift? The suspended weight principle — a critical concept: the rule that "a suspended weight acts at the crane head" is fundamental to understanding crane operation stability. A 150-tonne weight resting on the quay has a specific KG. When it is lifted by the crane — it immediately becomes a 150-tonne PENDULUM suspended at the crane head height. From that moment, for stability calculation purposes, all 150 tonnes are at the crane head height. This can cause: (a) sudden loss of GM if the crane head is very high; (b) list if the crane is working over one side; (c) instability if the vessel was already marginal. Pre-lift stability (option B): the stability calculation at the final stowage position tells you about the vessel's final condition — it does NOT address the CRITICAL moment during the lift when the weight is suspended. The lift itself is the most dangerous moment for stability. Stability must be calculated for the WORST CASE during the lifting operation. Adding high-side ballast (option D): this is the angle of loll error applied to craning. Adding ballast to the high side RAISES G (bad if GM is already reduced from the suspended weight). The correct approach is to pre-ballast LOW BALLAST (double bottom) BEFORE the lift to lower G and provide adequate GM reserve throughout the lifting operation. Master's role in crane operations (option C): the master is responsible for all operations on the vessel. Heavy lift operations are an ISM-covered activity requiring: (a) risk assessment; (b) PTW; (c) stability verification; (d) weather window decision. The crane operator (crane driver) manages the crane physically — the master oversees the overall operation and makes the go/no-go decision.

Question 2

Before departure from Durban, your stability program shows the vessel meets 5 of the 6 IS Code criteria but the righting lever arm at 30° (GZ at 30°) is 0.18m against the required minimum of 0.20m. What do you do?

Accepted Answer

IS CODE CRITERIA — GZ AT 30° DEFICIENCY: THE SIX IS CODE CRITERIA (MSC.267(85) — IS Code 2008): the International Stability Code mandates SIX stability criteria that ALL must be satisfied: (1) Area under GZ curve from 0° to 30° ≥ 0.055 m·rad; (2) Area under GZ curve from 0° to 40° ≥ 0.090 m·rad; (3) Area under GZ curve from 30° to 40° ≥ 0.030 m·rad; (4) GZ AT 30° ≥ 0.200m; (5) MAXIMUM GZ at angle ≥ 25°; (6) GM₀ ≥ 0.150m. FAILING ONE CRITERION MEANS FAILURE: all six criteria must be satisfied simultaneously. A GZ at 30° of 0.18m (vs required 0.20m) is a FAILURE — the vessel does NOT meet IS Code intact stability criteria. THE VESSEL CANNOT DEPART: it would be UNSEAWORTHY for the intended sea voyage. REMEDIES — HOW TO CORRECT THE DEFICIENCY: (1) REDUCE CARGO: if cargo is high in the vessel, shifting weight lower increases the GZ at 30°; (2) LOWER THE G: reduce KG by: (a) Adding low ballast (double bottom tanks); (b) Removing top-heavy weights; (c) Shifting cargo lower; (3) INCREASE BEAM LOADING: for certain hull forms, a different loading pattern affects the GZ curve shape; (4) REDUCE FREE SURFACE: if slack tanks are contributing to reduced GM — fill or empty tanks to remove free surface effect; DOCUMENTATION: the master must not sail with a stability calculation showing non-compliance. This is ISM non-conformity — notify DPA. LEGAL: departure with known stability non-compliance = MSA 1995 Section 58 offence (taking an unseaworthy ship to sea). IS Code — mandatory treaty obligation: the International Stability Code (IS Code 2008, MSC.267(85)) is mandatory under SOLAS Regulation II-1/5-1. It is not guidance — it is a mandatory standard with which ALL ships must comply. Failing ONE criterion fails ALL six — they are not averaged. "Close enough" margin (option B): there is no concept of "within tolerance" for IS Code criteria. The 0.20m GZ at 30° is a minimum — not an average. A calculated value of 0.18m is non-compliant. Stability programs have their own accuracy considerations — but if the calculation shows 0.18m, the vessel is non-compliant and must be remedied before departure. Charterer responsibility (option C): the charterer prescribes the cargo but the MASTER is responsible for the stability of the loaded vessel. The master must assess the proposed loading plan and refuse to sail if the result is non-compliant. The master can agree with the charterer to adjust the loading to achieve compliance (different stowage, reduced quantity, added ballast) — but the master cannot blame the charterer for a stability failure. IS Code as guideline (option D): this is completely incorrect. The IS Code is cited in SOLAS and is a mandatory instrument for all flag states that have ratified SOLAS. It is enforced by flag state surveyors, classification societies, and PSC inspectors. A vessel that departs without meeting IS Code criteria is unseaworthy in law and the master faces criminal liability under MSA 1995 Section 58. What "GZ at 30° ≥ 0.20m" means physically: GZ is the righting lever — the horizontal distance between the line of action of buoyancy and gravity at a given angle of heel. A GZ of 0.20m at 30° means the restoring couple (GZ × displacement) is providing a meaningful self-righting force at that angle. Below 0.20m, the vessel has reduced ability to recover from a 30° heel — which in heavy weather could develop into capsize.

Question 3

Your vessel is listing to starboard at a steady angle of approximately 8°. The deck officer believes this is a list due to off-centre cargo but the second officer suspects angle of loll. How do you distinguish, and what are the correct actions?

Accepted Answer

ANGLE OF LOLL vs LIST — IDENTIFICATION AND RESPONSE: DISTINGUISHING FEATURES: (1) LIST (caused by off-centre weight): (a) The vessel rests to one side; (b) GM is POSITIVE; (c) The GZ curve is displaced sideways but still positive; (d) Filling a tank on the high side (away from the list) will CORRECT the list; (e) The vessel has a definite "preferred" upright position but is offset by the asymmetric loading; (2) ANGLE OF LOLL (caused by NEGATIVE GM): (a) The vessel has ZERO or NEGATIVE GM; (b) The GZ at zero degrees is ZERO; (c) The vessel has no stable upright position — it lolls to one side where the GZ curve has positive values; (d) The vessel may flop between loll to port and loll to starboard; (e) IDENTIFYING CHARACTERISTIC: if you forcibly push the vessel further to the loll side — it continues to heel further. If you push a listed vessel — it resists and returns; HOW TO DISTINGUISH ON THE VESSEL: (1) Look at the GZ curve from the loading computer: is GM positive (list) or zero/negative (loll)?; (2) Apply a small external force: does the vessel resist (list) or comply (loll)?; CORRECT ACTION FOR LOLL: (1) DO NOT FILL HIGH-SIDE DOUBLE BOTTOM TANKS FIRST: the counter-intuitive nature of loll. Adding ballast on the high side RAISES the centre of gravity FURTHER — makes GM MORE negative — the loll worsens. The vessel may VIOLENTLY FLOP to the opposite side; (2) CORRECT ACTION: add ballast SYMMETRICALLY to the LOWEST point first. Fill lowest double bottom tanks evenly port and starboard to lower G and raise GM above zero; (3) NOTIFY DPA: this is a serious stability situation. Why high-side ballasting is FATAL in angle of loll: this is the most counter-intuitive and critical point in the angle of loll topic. At angle of loll with negative GM: (a) Adding ballast to the high side raises G because the ballast centre is higher than the vessel's current G; (b) This makes GM MORE negative; (c) The loll worsens; (d) Suddenly adding water to a high-side tank when GM is negative can cause the vessel to VIOLENTLY FLOP to the other side through the unstable upright position; (e) The violent flop has caused capsizes and cargo losses in practice. The asymmetric ballast (option D): cross-flooding from the loll side to the high side raises G on both sides. If the cross-flooding ALSO raises G (because the tanks are above the existing G) — it makes things worse. The principle remains: lower double bottom tanks first, symmetrically. The violent flop: at an angle of loll, the vessel is in stable equilibrium AT the loll angle. As you correct the negative GM (by adding weight low down), there is a brief period where the vessel passes through UNSTABLE equilibrium at the upright position before developing positive stability. During this passage through zero stability, ANY external force (wave, wind) can cause a rapid angle change. The vessel may flop to the other loll angle. Crew and cargo must be secured during the corrective process. 8° list is acceptable (option C): a static 8° list at sea is NOT acceptable and is not normal. It indicates either asymmetric loading (which should be corrected) or reduced stability (angle of loll — which is dangerous). Any unexpected and persistent list requires investigation and correction.