Chapter 2

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Stability

2.1 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 a very useful aid in verifying the actual stability conditions.

2.2 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;
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.

2.3 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.

2.4 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^* .

2.5 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 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 manual.

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* Reference is made to resolution A.167(ES.IV) as amended by resolution A.206(VII) - “Recommendation on intact stability for passenger and cargo ships under 100 m in length, as amended, with respect to ships carrying timber deck cargoes.”

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