Section 5 Stabiliser arrangements

5.1.1 The scantlings, arrangements and effectiveness of the stabilizers are outwith the scope of classification; however their foundations, supporting structure and watertight integrity are to be examined.

5.2.1 Detailed plans are to be submitted clearly indicating the positions, supporting structures and design loads for retractable and non-retractable fin stabilisers.

5.2.2 The design, construction, operational performance and control of fin stabilisers are outside the scope of classification.

5.2.3 Stabiliser fins are to be positioned so that the openings for the fins are between a pair of transverse watertight bulkheads which form a watertight compartment. Where stabiliser fins extend across watertight bulkheads, these bulkheads are not included in the compartment definition, see Figure 3.5.1 Stabiliser fin positioning. If this compartment is subjected to flooding due to stabiliser damage, calculations and information are to be submitted showing that the bulkhead deck does not become submerged and that essential systems remain operational. A water ingress detector and alarm are to be provided, as well as indication on the navigation bridge.

Figure 3.5.1 Stabiliser fin positioning

5.2.4 Shell insert plates are to be fitted or, for composite craft, laminate thickness increased in way of stabilisers. The thickness of the insert plate or increased laminate is to be at least 50 per cent greater than the shell thickness in way, and is to extend over a minimum area formed by 1,25 times the stabiliser root chord length ‘c’ and covering all operational angles of the fin, see Figure 3.5.2 Shell insert or increased laminate. In addition, for retractable stabilisers the insert is to extend beyond the shell opening for a distance of not less than 25 per cent of the length of the root chord. The insert plate is to extend above and below the opening for the stabiliser for a minimum distance equal to the opening height.

Figure 3.5.2 Shell insert or increased laminate

5.2.6 Supporting direct calculations are to be submitted for the load cases in Pt 3, Ch 3, 5.2 Fin stabilisers 5.2.5 demonstrating compliance with the allowable stresses.

5.2.7 Shaft bearing materials and seals are to be of an approved type.

5.2.8 For craft constructed of steel or aluminium the watertight enclosure into which the stabilisers retract is to have a perimeter plating thickness of the surrounding shell plating plus 2 mm and stiffened to an equivalent standard.

5.2.9 For craft constructed of composite materials the laminate thickness of the watertight enclosure into which the stabilisers retract is to have a thickness not less than the surrounding shell laminate.

5.2.10 Non-retractable or retracted stabiliser fins are, in general, not to extend beyond the beam of the hull or below the keel.

5.2.11 In general, full penetration welds are to be applied in way of the stabiliser pedestal and surrounding hull structure. Welds are to be smooth and notch-free. Construction details are to be carefully designed to avoid structural discontinuities and stress concentrations.

5.2.12 On ice class ships, non-retractable stabiliser fins are not to be fitted to ships with an Ice Class 1C or higher. Where fitted, the fins are to be positioned at least 500 mm below the ice light waterline in all operating positions.

5.3.1 The general structure of the tank is to comply with the Rule requirements for deep tanks. Sloshing forces in the tank structure are to be taken into account. Where such forces are likely to be significant, the scantlings will be required to be verified by additional calculations.

5.4.1 The scantlings, arrangements and effectiveness of ride control systems are currently outwith the scope of classification; however their foundations, supporting structure and watertight integrity together with the associated reaction forces on the hull structure are to be examined. Details of the loadings and supporting calculations are to be submitted with the relevant construction plans for consideration.

5.5.1 Motion damping devices are generally outwith the scope of the Rules. Where motion damping devices are fitted the designers/Builders are to submit details of the anticipated loadings and supporting calculations for appraisal of the adjacent hull structure.

5.6.1 Where the Rules do not specifically define the requirements for novel features then the scantlings and arrangements are to be determined by direct calculations. Such calculations are to be carried out on the basis of the Rules, Recognised Standards and good practice, and are to be submitted for consideration.