Appendix – Definitions and Interpretations
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Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC.1/Circular.1461 – Guidelines for Verification of Damage Stability Requirements for Tankers – (08 July 2013) - Annex – Guidelines for Verification of Damage Stability Requirements for Tankers - Appendix – Definitions and Interpretations

Appendix – Definitions and Interpretations

  1 A stability instrument is an instrument installed on board a particular ship by means of which it can be ascertained that stability requirements specified for the ship in the Stability Booklet are met in any operational loading condition. A stability instrument comprises hardware and software.

  2 There are three types of stability software, details of which are provided in chapter 4 of part B of the 2008 IS Code and MSC.1/Circ.1229. A brief description of the three types is as follows. Three types of calculations performed by stability software are acceptable depending upon a ship's stability requirements:

  • Type 1: Software calculating intact stability only (for ships not required to meet a damage stability criterion);

  • Type 2: Software calculating intact stability and checking damage stability on the basis of a limit curve (e.g. for ships which apply to SOLAS chapter II-1, part B-1 damage stability calculations, etc.) or previously approved loading conditions; and

  • Type 3: Software calculating intact stability and damage stability by direct application of pre-programmed damage cases for each loading condition (for some tankers, etc.).

  3 Approved loading condition

  3.1 In relation to a tanker certified under MARPOL Annex I or the IBC or IGC Codes, an approved loading condition is a unique individual condition of loading, taking account of the combination of lightship and all individual deadweight items, which has been verified by the Administration or RO acting on its behalf as complying with both intact and damage stability criteria, and is approved for use in the service of the ship.

  3.2 The approval of an individual loading condition is granted for the purpose of loading to that unique condition and cannot be taken to confer any acceptance or approval of other loading conditions which vary from it, given that the margin of compliance against the applicable intact or damage stability criteria may be zero.

  3.3 Loading conditions which are verified in service and shown to lie within the boundary of an approved range of loading conditions or approved limiting KG/GM curves shall also be regarded as approved loading conditions.

  3.4 Loading conditions which are verified using an approved stability instrument authorized by the Administration or RO acting on its behalf should also be regarded as approved loading conditions.

  4 Loading "in accordance with", "closely to" or "not significantly different from" an approved loading condition

  4.1 For tankers which do not have an approved stability instrument, an approved range of loading conditions or critical GM or KG data, which enable damage stability verification of the live loading condition to be made on board prior to departure, loading should always be made strictly in accordance with an approved loading condition unless the loading condition is first verified as compliant by the Administration or RO acting on its behalf prior to departure.

  4.2 However, to permit practical operation of such tankers, having regard to small variations in cargo SG, stores and minor tank fillings, it is considered necessary to permit some variation in loading from an approved condition.

  4.3 In this respect, it is recommended that a vessel which loads within the boundary provided by an approved pair of departure and arrival conditions, derived from a fixed distribution of cargo and ballast, may be considered to be loaded in accordance with these conditions.

  4.4 To satisfy this recommendation, the live loading condition should fall within the following limits:

  • .1 displacement, to fall within the range of displacements of the approved departure and arrival conditions;

  • .2 KG/GM (corrected for free surface) to fall below a value determined by linear interpolation at the live condition displacement between the approved departure and arrival conditions used to verify damage stability compliance; and

  • .3 trim, to fall within the range of trims described by those of the approved departure and arrival conditions.

  4.5 No further relaxations or deviation should be allowed, unless specifically approved by the Administration.

  5 Approved range of loading conditions

  5.1 It is acceptable to load to a condition of loading which is defined within a range of approved loading conditions.

  5.2 For an approved range of loading conditions to be valid it must offer a clear indication how cargoes and ballast are to be loaded.

  5.3 In this respect, all parameters of loading defined within an approved range of loading conditions must be fully complied with for a vessel to be considered correctly loaded within it.

Parent topic: Annex – Guidelines for Verification of Damage Stability Requirements for Tankers
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