Your vessel is loading timber deck cargo to the weather deck. Describe the TDC Code requirements and the stability implications of the timber freeboard allowance.

A. TIMBER DECK CARGO — TDC CODE AND STABILITY: TDC CODE (MSC.287(87)) — MANDATORY: the Timber Deck Cargo Code (as revised) applies to all vessels carrying timber on exposed decks. TIMBER FREEBOARD ALLOWANCE: the Load Line Convention allows a REDUCED FREEBOARD for vessels carrying timber deck cargo. This "timber freeboard" is less than the standard Load Line freeboard — meaning the vessel can be loaded deeper than normal. RATIONALE FOR REDUCED FREEBOARD: the timber deck cargo itself provides additional reserve buoyancy (it is inherently buoyant and adds volume above the waterline that resists flooding). CONDITIONS FOR TIMBER FREEBOARD: to use the timber freeboard (reduced freeboard = loaded deeper): (a) The timber must meet the TDC Code requirements: properly stowed, secured, and distributed; (b) The hatch covers and weathertight integrity must be confirmed; (c) The stability must meet BOTH the IS Code criteria AND the specific TDC Code stability criteria (which consider: timber wind heeling moment, increased sail area from timber stacks, and water absorption allowance); STABILITY IMPLICATIONS — WATER ABSORPTION: a critical TDC Code provision: as the voyage progresses, the timber on deck absorbs seawater. This WEIGHT INCREASE must be accounted for. The TDC Code specifies a water absorption allowance that is added to the stability calculation for the arrival condition. Typically, the allowance assumes 15% weight increase from absorption; (d) Windage area: high timber stacks present significant windage, affecting the heeling moment in beam winds. The TDC Code stability criteria include an enhanced wind heeling moment calculation; LASHING: the timber must be secured with chains, wire, or straps rated to the TDC Code requirements. Lashing inspections must be conducted regularly during the voyage.

B. Timber deck cargo can be loaded to the maximum possible draught as the timber provides unlimited reserve buoyancy.

C. The timber freeboard allowance removes the IS Code stability requirement. Vessels using timber freeboard are exempt from the standard stability criteria.

D. Water absorption of timber is negligible. The arrival stability calculation is the same as departure calculation for timber deck cargo.

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.