4.3 Model set-up

  4.3.1.1 The model should be built geometrically scaled up to the upper weather deck including forecastle and bulwarks and be sufficiently rigid with a smooth finish. The whole model (excluding free flooded spaces) should be watertight in order to guarantee hydrostatic properties.

  4.3.1.2 All superstructures included in stability calculations or that are submerged during the tests should be reproduced to scale to ensure the model has the correct righting arm curve. Superstructures that do not submerge during the tests described below can be omitted.

  4.3.1.3 Appendages such as bilge keels or rudder should be fitted, properly scaled and the report should state which appendages were fitted during the tests.

 To avoid scale effect on roll damping, the model overall length should be at least 2 m. However, the model should be scaled up, if necessary, to make the breadth of the bilge keels greater than 7 mm. For monohull ships having neither bilge keels nor sharp bilges^footnote, however, the model overall length should be at least 4 m unless frictional effect on roll damping is corrected with theoretical methods described later, but in any case not less than 2 m or a scale 1:75, whichever is greater.

  4.3.3.1 The model should be ballasted to the appropriate displacement and loading condition for the ship. To ensure correct displacement and attitude, draught marks or suitable gauges should be used. Weights should be adjusted to achieve the correct position of the centre of gravity.

  4.3.3.2 Weight distribution should be such as to guarantee reasonable radius of gyration for pitch. Unsymmetrical weights distribution should be avoided as far as practicable.

  4.3.3.3 Inclining tests should be carried out to verify that the value of ship’s metacentric height GM corresponds to that of the actual ship within an error of 2% or 1 mm at model scale, whichever is larger.

  4.3.3.4 In addition, depending on the information provided to the model basin, natural roll period TΦ in water or roll radius of gyration in air, should be checked to correspond to that provided within an error of 2%.

 The ship natural roll period should be used for tests. In case a sufficiently accurate estimation of Tφ is not available at the time of tests, they should be carried out for a series of at least 3 different roll periods, from which the results can be finally interpolated for the actual ship roll period.