What is Minimum IMO stability criteria for ships carrying timber deck cargoes ?

As per Chapter 4 Regulation 4.1 of the Code on Intact Stability

Details the minimum intact stability requirements for cargo ships 24 metres 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 following requirements:

  1. The area under the righting lever curve (GZ curve) should not be less than 08 metreradians
  2. Upto 40 degree heel or the angle of down flooding if this angle is less than 40 degree.
  3. The maximum value of the righting lever (GZ) should be at least 25 m.
  4. At all times during the voyage, the metacentric height (GM) 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 of the Code)
  5. When determining the ability of the ship to withstand the combined effects of beam wind and rolling (Regulation 3.2 of the Code; section 24.1.2.2 of this text) the 16 degree limiting angle of heel under the action of steady wind should be complied with, but the additional criterion of 80% of the angle of deck edge immersion may be ignored.
Note :

The stability of the ship must be positive at all times and should be calculated having regard to:

  • The increased weight of the timber deck cargo due to:
    • absorption of water, and;
    • ice accretion if applicable;
  • Variations in consumables (such as fuel consumption from tanks low down in the ship);
  • The free surface effects of liquids in tanks, and;
  • Weight of water trapped in broken spaces within the timber deck cargo and especially logs.
  • Ships carrying timber deck cargoes should operate, as far as possible, with a margin of safety with respect to metacentric height (GM), however the metacentric height should preferably not exceed 3% of the breadth of the ship in order to prevent excessive accelerations in rolling that would cause large racking stresses and high stresses on cargo lashings which might result in cargo loss or shift.

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