Section 4 Fixed and steering nozzles, bow and stern thrust units

4.1.1 Fixed and steering nozzles are, in general, to be in accordance with Pt 3, Ch 13, 3 Fixed and steering nozzles of the Rules and Regulations for the Classification of Ships, July 2022.

4.2.1 For the requirements of steering gear, see Pt 12, Ch 1 Propellers.

4.3.1 The wall thickness of the unit is, in general, to be in accordance with the manufacturer's practice, but is to be not less than:

1. For steel hulls, the thickness of the adjacent shell plating plus 10 per cent or 2 mm whichever is the greater, subject to a minimum of 7 mm.

2. For aluminium hulls, the thickness of the adjacent shell plating plus 10 per cent or 1 mm whichever is the greater, subject to a minimum of 8 mm.

3. For FRP hulls, generally the thickness of the adjacent shell laminate plus 25 per cent subject to a minimum of 8 mm. Full details of the proposed laminate and resin system are to be submitted for approval.

4.4.1 The method of attachment of the tube is dependent upon the tube and the craft's construction materials which may be steel, aluminium alloy or FRP.

4.4.2 The tunnel tube is to be fitted either between a pair of deep floors or bulkheads extending to above the design waterline or in a separate watertight compartment.

4.4.3 The shell plating thickness is to be locally increased by 50 per cent in way of tunnel thruster connections.

4.4.4 For welded tube connections the welding is to be by full penetration welding.

4.4.5 For FRP tubes attached by bonding the total bonding reinforcement weight is to be at least that of the hull bottom laminate with the tube bonded internally and externally to the shell laminate. Prior to bonding in situ the areas to be bonded are to be thoroughly abraded and degreased and all cut FRP laminate edges resin sealed.

4.4.6 The tunnel tube is to be framed to the same standard as the surrounding shell plating.

4.4.7 The unit is to be adequately supported and stiffened.

4.5.1 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 be carried out on the basis of the Rules, recognised standards and good practice, and are to be submitted for consideration.