Your loading program shows GM = 0.95m before free surface correction. You have 4 slack tanks each with a free surface moment of 250 tonne-metres. Displacement is 15,000 tonnes. Calculate the effective GM and assess.

A. FREE SURFACE EFFECT CALCULATION: FREE SURFACE EFFECT FORMULA: Loss of GM (GGv) = Free Surface Moment (FSM) / Displacement. TOTAL FREE SURFACE MOMENTS: 4 tanks × 250 t·m each = 1,000 tonne-metres total. LOSS OF GM: GGv = 1,000 t·m / 15,000 t = 0.0667m (approximately 0.067m). EFFECTIVE (CORRECTED) GM: GMeff = GM (solid) - GGv = 0.95m - 0.067m = 0.883m. ASSESSMENT: (a) IS Code minimum GM₀ = 0.150m — EASILY MET (0.883m is well above); (b) Grain Code minimum (if applicable) GM₀ = 0.300m — MET; (c) The free surface correction is significant but the resulting effective GM is very healthy; (d) The vessel is in a stable condition; PRACTICAL GUIDANCE ON SLACK TANK MANAGEMENT: (1) MINIMISE THE NUMBER OF SLACK TANKS: fill tanks either full or empty where possible. A completely full tank has zero free surface moment; (2) SMALL TANKS HAVE SMALL FREE SURFACE: if you must have slack tanks — prefer smaller tanks over larger tanks. Free surface moment increases with the cube of the tank width; (3) LONGITUDINAL DIVIDING PLATES: tanks with a centerline division have significantly reduced free surface moments (each half is a smaller tank); (4) CRITICAL POINT: free surface effect is a VIRTUAL rise in G — it acts regardless of whether the slack liquid is ballast, fuel, fresh water, or cargo. All slack tanks must be included in the stability calculation.

B. Free surface effect only applies to ballast tanks. Fuel and fresh water tanks are fixed and do not contribute to free surface moments.

C. With GM of 0.95m the vessel is so stable that free surface correction is not required. A large GM makes the vessel immune to free surface effects.

D. Fill all tanks completely to eliminate free surface effect before any calculation. Partly-filled tanks invalidate the stability calculation.

A. 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).

B. The vessel is close enough to the 0.20m requirement. A margin of 0.02m is within normal calculation tolerance and the vessel can depart.

C. Consult the charterer. As the cargo interests are driving the loading plan, the charterer is responsible for stability compliance.

D. Only the stability program minimum acceptable values matter for commercial voyages. IS Code criteria are guidelines, not mandatory requirements.

A. 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.

B. Fill the high-side (port) double bottom tanks immediately. Adding ballast to the high side always corrects any form of list or loll.

C. An 8° list at sea is normal and acceptable. No action is required unless the angle increases beyond 15°.

D. Open the cross-flooding valves to transfer ballast from the starboard to the port tanks. Cross-flooding always corrects asymmetric stability issues.