Stability and Damage Control as Applied to Machinery Spaces
This domain applies stability to the machinery spaces: what happens when a tank or the engine room floods, how free surface reduces stability, and how damage control is organised before the water arrives.
Rules
- Intact stability: IMO criteria include area under the GZ curve to 30 degrees of at least 0.055 m.rad, to 40 degrees of at least 0.09 m.rad, maximum GZ of at least 0.2 m at an angle of at least 30 degrees, and initial GM of at least 0.15 m.
- Free surface: FSM = density x i, and loss of GM = FSM / displacement. Longitudinal divisions cut the free surface roughly with the square of the number of divisions.
- Damage control: know the watertight subdivision, the damage control plan, the emergency bilge suction location, and the sequence for closing and opening.
Worked example
A rectangular tank 10 m long and 8 m wide is partly filled with seawater. i = 10 x 8 cubed / 12 = 426.7 m4. FSM = 1.025 x 426.7 = 437.3 t.m. For a displacement of 8,000 t, GM is reduced by 437.3 / 8,000 = 0.055 m. Against a 0.15 m margin, one slack tank uses more than a third of it.
Traps
Forgetting to subtract FSM from GM; assuming a pressed-up tank has free surface; treating a flooded engine room as a simple weight addition with no free surface or permeability.