A damage stability criterion varies from ship to ship and the requirement for the same is given in SOLAS chapter II-1. It may be single compartment flooding, multi compartment flooding, engine room flooding etc.
Under all the criteria as applicable, vessel margin line should not be submerged after the damage. Margin line is an imaginary line drawn 76mm below the free board deck.
Basic Pre-Departure Checks
- Longitudinal Strength – Load Line
- Intact Stability – Load Line
- Damage Stability
- Oil Tankers – Marpol Annex 1, reg 25
- Gas Tankers – IGC Code, Chapter 2
- Chemical Tankers – IBC Code, Chapter 2
- Approved Stability Information
– Intact loading Conditions
– Damage Calculations
-Oil Tankers – IOPP Certificate and Form B
-Gas Tankers – Certificate of Fitness
-Chemical Tankers – Certificate of Fitness
IGC and IBC Certificates of Fitness:
That the ship must be loaded:
.1 in accordance with the loading conditions provided in the approved loading manual, stamped and dated ……………………………………………………. and signed by a responsible officer of the Administration, or of an organization recognized by the Administration; or
.2 in accordance with the loading limitations appended to this Certificate.
Where it is required to load the ship other than in accordance with the above instruction, then the necessary calculations to justify the proposed loading conditions should be communicated to the certifying Administration who may authorize in writing the adoption of the proposed loading condition.
IACS Resolutions • UR L5 “Onboard Computers for Stability Calculations”; Typical Stability Approval at Build
- Intact stability information booklet
–Contains sample intact loading conditions.
–On approval, these intact loading conditions are themselves deemed to be “approved” for use.
- Damage stability appraisal
–Usually a separate submission
–Demonstrates only that the approved intact loading conditions will survive the extent of damage required by the applicable Convention or Code, and achieve the minimum residual stability standard.
In this approach damage is applied directly to the approved intact loading conditions on a case by case basis. The results, and the approval, is therefore conditional upon the assumption that the following parameters remain unchanged in the loaded vessel, otherwise damage results may be adversely affected :
- Cargo SG
- Draught and or Trim
- Empty/Part Filled Cargo Tanks
- Cargo or Ballast Distribution
- Use of Deck Tanks
Various Damage Conditions:
This example of a damage stability appraisal for a coastal tanker shows the typical scale of peak residual GZ values for each loading condition in the final column.
For all loading conditions, the initial metacentric height and the righting lever curve should be corrected for the effect of free surfaces of liquids in tanks. Superstructures and deckhouses not regarded as enclosed can be taken into account in stability calculations up to the angle at which their openings are flooded.
Full compliance with residual stability criteria must be achieved before any such point becomes immersed. When determining the righting lever (GZ) of the residual stability curve, the constant displacement (lost buoyancy) method of calculation should be used .
Operational documentation: loading and stability information booklet (stability booklet), Damage Control Plan; and Damage Control Booklet 2).
Direct calculation onboard (Stability software)
Stability software installed onboard should cover all stability requirements (intact and damage) applicable to the ship.
a) Type 2: Checking intact and damage stability on basis of a KG/GM limit curve(s) or previously approved loading conditions; and
b) Type 3: Checking intact and damage stability by direct application of pre-programmed damage cases for each loading condition, including capability for calculation of intermediate damage stages.
The software should be approved by the classification society. The software is not a substitute for the approved stability documentation, but used as a supplement to facilitate stability calculations. Sufficient damages, taking into account lesser damages, and variation of draft, cargo density, tank loading patterns and extents of tank filling should be performed to ensure that for any possible loading condition the most onerous damages have been examined according to relevant stability criteria.
The verification of KG/GM limit curves should be conducted without any free surface correction. The actual loading condition uses the free surface correction when comparing actual and allowable KG values. It is to be noted that any change of filling level, draught, trim, cargo density might have a major influence to the results of a damage case; therefore the following items should be considered carefully for the calculation of the KG/GM limit curves:
a) Intact and damage stability criteria applicable to the vessel;
b) The maximum required damage extent and lesser extents of damage which provide the most severe damage cases;
c) Draught range of the vessel (up to tropical freeboard if required);
d) Trim range of the vessel (see paragraph 6.6);
e) Full and empty cargo tanks;
f) Partially filled cargo tanks (consideration of increments as necessary);
g) Minimum tank fillings in tonnes if required;
General documents and supporting information
.1 lines plan, plotted or numerically;
.2 hydrostatic data and cross curves of stability (including drawing of the buoyant hull);
.3 definition of watertight compartments with moulded volumes, centres of gravity and permeability;
.4 layout plan (watertight integrity plan) for the watertight compartments with all internal and external opening points including their connected sub-compartments, and particulars used in measuring the spaces, such as general arrangement plan and tank plan;
.5 Stability Booklet/Loading Manual including at least fully loaded homogeneous condition at summer load line draught (departure and arrival) and other intended operational conditions;
.6 coordinates of opening points with their level of tightness (e.g., weathertight, unprotected) 2), including reference to the compartment that the opening is connected to.
.7 watertight door location;
.8 cross and down flooding devices and the calculations thereof according to resolution MSC.245(83) with information about diameter, valves, pipe lengths and coordinates of inlet/outlet. Cross/down flooding should not be considered for the purpose of achieving compliance with the stability criteria (see also paragraph 9.2);
.9 pipes in damaged area when the breaching of these pipes results in progressive flooding (see paragraph 10.1);
.10 damage extents and definition of damage cases; and
.11 any initial conditions or restrictions which have been assumed in the derivation of critical KG or GM data, and which must therefore be met in service
Damage Control Plan
For passenger and dry cargo ships for which a damage stability calculation is to be performed a Damage Control Plan is to be prepared, containing the following information if applicable and partly beyond the requirements of MSC/ Circ. 919:
✓ ship’s name ✓ Shipyard and hull no. ✓ Class-register-no, Character of Classification and damage stability marking ✓ principal dimensions ✓ permissible number of persons to be carried ✓ subdivision index R ✓ main and local watertight subdivision ✓ numbering of compartments ✓ frame numbers and spacing ✓ penetration lines (e.g. B/5 or 760 mm-line) in each deck view ✓ simplified instructions in case of damage in order to prevent progressive flooding ✓ emergency exits ✓ watertight door location with control stations ✓ position of weathertight and unprotected opening points ✓ pipes in damaged area when the destruction of these pipes results in progressive flooding ✓ valves at bulkheads penetrations ✓ cross- and down flooding arrangement ✓ permanent solid or liquid ballast or min./max. q
Damage Control Booklet
In addition to the aforementioned, booklets shall be made available according to MSC/Circ. 434 and MSC/Circ. 919 containing the following information:
✓ introduction and description of this manual ✓ principal dimensions and main data ✓ stability limiting values (VCG/GM limit curve) ✓ ship’s watertight arrangement ✓ position of watertight doors and hatches with ✓ information about operational instructions ✓ position of all weathertight and unprotected openings ✓ piping arrangement incl. available pumps and ✓ valve arrangement ✓ cross- and downflooding arrangement ✓ summary of the damage stability calculation with description of the analysis concept and damage stability criteria ✓ information of the damage control locations ✓ position of sounding devices
The main purpose of such a document is to stipulate appropriate action in case of damage. The chapter for damage control should include information such as:
• workflow of damage scenario • closing of watertight and weathertight openings • check of the extent of damage and sounding of compartments • use of pumps • use of loading computer • liquid transfer operations • information to external authorities and emergency response group The booklet should be supplemented with copies of the general arrangement plan, tank capacity plan and piping diagram as well as information about used abbreviations and the definition of the co-ordinate system.