4.1 Cargo ships carrying timber deck cargoes

 The provisions given hereunder apply to all ships of 24 m in length and over engaged in the carriage of timber deck cargoes. Ships that are provided with and make use of their timber load line should also comply with the requirements of the regulations 41 to 45 of the Load Line Convention.

 The following definitions apply for the purposes of the present section:

• .1 timber means sawn wood or lumber, cants, logs, poles, pulpwood and all other types of timber in loose or packaged forms. The term does not include wood pulp or similar cargo;

• .2 timber deck cargo means a cargo of timber carried on an uncovered part of a freeboard or superstructure deck. The term does not include wood pulp or similar cargo;^footnote

• .3 timber load line means a special load line assigned to ships complying with certain conditions related to their construction set out in the International Convention on Load Lines and used when the cargo complies with the stowage and securing conditions of the Code of Safe Practice for Ships Carrying Timber Deck Cargoes, 1991 (resolution A.715(17)).

 For ships loaded with timber deck cargoes and provided that the cargo extends longitudinally between superstructures (where there is no limiting superstructure at the after end, the timber deck cargo should extend at least to the after end of the aftermost hatchway)^footnote transversely for the full beam of ship after due allowance for a rounded gunwale not exceeding 4% of the breadth of the ship and/or securing the supporting uprights and which remains securely fixed at large angles of heel, the Administration may apply the following criteria which substitute those given in 3.1.2.1 to 3.1.2.4 and 3.2:

• .1 The area under the righting lever curve (GZ curve) should not be less than 0.08 metre-radians up to θ = 40° or the angle of flooding if this angle is less than 40°.

• .2 The maximum value of the righting lever (GZ) should be at least 0.25 m.

• .3 At all times during a voyage, the metacentric height GM_o should not be less than 0.10 m after correction for the free surface effects of liquid in tanks and, where appropriate, the absorption of water by the deck cargo and/or ice accretion on the exposed surfaces. (Details regarding ice accretion are given in chapter 5).

• .4 When determining the ability of the ship to withstand the combined effects of beam wind and rolling according to 3.2, the 16° limiting angle of heel under action of steady wind should be complied with, but the additional criterion of 80% of the angle of deck edge immersion may be ignored.

  4.1.4.1 The ship should be supplied with comprehensive stability information which takes into account timber deck cargo. Such information should enable the master, rapidly and simply, to obtain accurate guidance as to the stability of the ship under varying conditions of service. Comprehensive rolling period tables or diagrams have proved to be very useful aids in verifying the actual stability conditions.^footnote

  4.1.4.2 For ships carrying timber deck cargoes, the Administration may deem it necessary that the master be given information setting out the changes in deck cargo from that shown in the loading conditions, when the permeability of the deck cargo is significantly different from 25% (see 4.1.6 below).

  4.1.4.3 For ships carrying timber deck cargoes, conditions should be shown indicating the maximum permissible amount of deck cargo having regard to the lightest stowage rate likely to be met in service.

  4.1.5.1 The stability of the ship at all times, including during the process of loading and unloading timber deck cargo, should be positive and to a standard acceptable to the Administration. It should be calculated having regard to:

• .1 the increased weight of the timber deck cargo due to:

  • .1.1 absorption of water in dried or seasoned timber, and

  • .1.2 ice accretion, if applicable (chapter 5);

• .2 variations in consumables;

• .3 the free surface effect of liquid in tanks; and

• .4 weight of water trapped in broken spaces within the timber deck cargo and especially logs.

  4.1.5.2 The master should:

• .1 cease all loading operations if a list develops for which there is no satisfactory explanation and it would be imprudent to continue loading;

• .2 before proceeding to sea, ensure that:

  • .2.1 the ship is upright;

  • .2.2 the ship has an adequate metacentric height; and

  • .2.3 the ship meets the required stability criteria.

  4.1.5.3 The masters of ships having a length less than 100 m should also:

• .1 exercise good judgement to ensure that a ship which carries stowed logs on deck has sufficient additional buoyancy so as to avoid overloading and loss of stability at sea;

• .2 be aware that the calculated GM_o in the departure condition may decrease continuously owing to water absorption by the deck cargo of logs, consumption of fuel, water and stores and ensure that the ship has adequate GM_o throughout the voyage;

• .3 be aware that ballasting after departure may cause the ship's operating draught to exceed the timber load line. Ballasting and deballasting should be carried out in accordance with the guidance provided in the Code of Safe Practice for Ships Carrying Timber Deck Cargoes, 1991 (resolution A.715(17)).

  4.1.5.4 Ships carrying timber deck cargoes should operate, as far as possible, with a safe margin of stability and with a metacentric height which is consistent with safety requirements but such metacentric height should not be allowed to fall below the recommended minimum, as specified in 4.1.3.

  4.1.5.5 However, excessive initial stability should be avoided as it will result in rapid and violent motion in heavy seas which will impose large sliding and racking forces on the cargo causing high stresses on the lashings. Operational experience indicates that metacentric height should preferably not exceed 3% of the breadth in order to prevent excessive accelerations in rolling provided that the relevant stability criteria given in 4.1.3 are satisfied. This recommendation may not apply to all ships and the master should take into consideration the stability information obtained from the ship's stability booklet.

 In addition to the provisions given in 3.6, the Administration may allow account to be taken of the buoyancy of the deck cargo assuming that such cargo has a permeability of 25% of the volume occupied by the cargo. Additional curves of stability may be required if the Administration considers it necessary to investigate the influence of different permeabilities and/or assumed effective height of the deck cargo.

 The loading conditions which should be considered for ships carrying timber deck cargoes are specified in 3.5.1.3. For the purpose of these loading conditions, the ship is assumed to be loaded to the summer timber load line with water ballast tanks empty.

 The following assumptions are to be made for calculating the loading conditions referred to in 4.1.7: the amount of cargo and ballast should correspond to the worst service condition in which all the relevant stability criteria of 3.1.2.1 to 3.1.2.4 or the optional criteria given in 4.1.3, are met. In the arrival condition, it should be assumed that the weight of the deck cargo has increased by 10% due to water absorption.

 The stowage of timber deck cargoes should comply with the provisions of chapter 3 of the Code of Safe Practice for Ships Carrying Timber Deck Cargoes, 1991 (resolution A.715(17)).^footnote