stability requirement

Stability Requirements for bulk grain

Vessels are required to demonstrate by calculation that at all times during a voyage the ship will have sufficient intact stability to provide adequate residual dynamic stability after taking into account the adverse heeling effects caused by an assumed pattern of grain shift within the void spaces lying directly above the grain.

The stability calculation is based on proving that the vessel will only list to a maximum of 12⁰ after experiencing: -

a)             a shift of cargo of 15⁰ in every full hold, plus;

b)             a shift of cargo of 25⁰ in any partly filled compartment.

·                The area between the heeling arm curve and the righting arm curve up to the angle of heel of the maximum difference between the ordinates of the two, or 40 degrees (or angle of flooding if less than 40⁰) must be at least 0.075 metre radians (see below).

·                Minimum initial GM = 0.3m

·                As many full compartments as possible

·                Cargo to be properly trimmed

Optional Stability Requirements for Ships WITHOUT a Document of Authorisation Loading PART Cargoes

·         Total weight of grain not to exceed one-third of the Dwt of the ship.

·         Longitudinal divisions or saucering and bagging required in filled compartments.

·         Partly filled compartments overstowed or strapped.

·         GM_f 0.30m or that given by the following formula, whichever is the greater: -

GM_R = L B V_d (0.25 B – 0.645  V_d B)

                        SF x     x  0.0875

Where: -

     

      L = total combined length of all full compartments

      B = moulded breadth of the vessel

      SF = stowage factor

      Vd = calculated average void depth

            = displacement

·         Master proves to Flag or Port State Control that the loaded condition complies with the requirements of the Code.

Stability Requirements for Existing Ships

• “Existing ships” – keels laid prior to 25 May 1980
• No restriction on dead-weight with regard to part cargoes

 Stowage

• Trim all grain surfaces level to minimise shifting
• Filled compartments trimmed to fill all under-deck spaces

Means to Reduce/Eliminate Shift of Cargo

In order to reduce the heeling moment to satisfy the requirements of the Code, the following action can be taken: -

 In filled, trimmed compartments

• A saucer of bulk grain in the hatchway, completely filled with bagged grain, OR;
• A bundle of bulk grain lashed in a saucer of bulk grain in a hatchway, OR;
• A longitudinal division placed in a hatchway.

 In partly filled compartments

• Over stowing a levelled surface of bulk grain with bagged grain, Or;
• A longitudinal division.

In order to eliminate the heeling moment to satisfy the requirements of the Code, the following action can be taken: -

• Strapping or lashing a slightly crowned surface of bulk grain, utilising separation cloths, lashings and either lumber dunnage or wire mesh.

 The strength of shifting boards, depth of saucers required and other details of the above arrangements are all stipulated in Part A of the Code, sections 14 to 18.