Section 2 Special features

2.1.1 The requirements for the construction and installation of water jet units apply irrespective of rated power.

2.1.2 Water jet ducts may be fabricated as an integral part of the hull structure, or as a bolted-in unit. In either case, detailed plans indicating dimensions, scantlings and materials of construction of the following are to be submitted in triplicate:

1. Arrangement of the system including intended method of attachment to the hull and building-in, geometry of tunnel, shell opening, method of stiffening, reinforcement, etc.

2. Shaft sealing arrangements.

3. Details of any shafting support or guide vanes used in the water jet system.

4. Details and arrangements of inspection ports, their closing appliances and sealing arrangement, etc.

5. Details and arrangements of protection gratings and their attachments.

2.1.3 When submitting the plans requested in Pt 7, Ch 5, 2.1 Water jet propulsion systems - Construction 2.1.2, details of the designers' loadings and their positions of application in the hull are to be submitted. These are to include maximum applied thrust, moments and tunnel pressures for which approval is sought.

2.1.4 All materials used in construction are to be manufactured and tested in accordance with the Rules for the Manufacture, Testing and Certification of Materials, July 2022(hereinafter referred to as the Rules for Materials).

2.1.5 Aluminium alloys are to be of suitable marine grades in accordance with the requirements of Pt 7, Ch 2, 2 Materials.

2.1.6 Irrespective of the material used, the strength and supporting structure of all tunnels are to be examined by direct calculation procedures which are to be submitted. In no case are the scantlings to be taken as less than the Rule requirements for the surrounding structure. The strength of the hull structure in way of tunnels is to be maintained. The structure is to be adequately reinforced and compensated as necessary. All openings are to be suitably reinforced and have radiused corners.

2.1.7 Consideration is to be given to providing the inlet to the tunnel with a suitable guard to prevent the ingress of large objects into the rotodynamic machinery. The dimensions of the guard are to strike a balance between undue efficiency loss due to flow restriction and viscous losses, the size of object allowed to pass and susceptibility to clog with weed and other flow restricting matter.

2.1.8 The inlet profile of the tunnel is to be so designed as to provide a smooth uptake of water over the range of craft operating trims and avoid significant separation of the flow into the rotating machinery.

2.1.9 Single or multiple water jet unit installations having a total rated power in excess of 500kW are to be contained within their own watertight compartment. Other arrangements for maintaining watertight integrity may be specially considered depending on the size and installation layout.

2.1.10 For details of machinery requirements, see Pt 12, Ch 2 Water Jet Systems.

2.2.1 Standard units built for `off the shelf' supply and which include the duct are to be installed strictly in accordance with the manufacturer's instructions, see also Pt 7, Ch 5, 2.1 Water jet propulsion systems - Construction 2.1.4.

2.2.2 Integral water jet ducts are to be constructed in accordance with the manufacturer's requirements and the relevant plans submitted as required by Pt 7, Ch 5, 2.1 Water jet propulsion systems - Construction.

2.2.3 Where load is transmitted into the transom and/or bottom shell, the thickness of the plating adjacent to the jet unit is to be increased. The increase in thickness is to be not less than 50 per cent of the calculated transom and bottom plating thicknesses respectively or 8 mm, whichever is the greater. Such reinforcement is to extend beyond the surrounding stiffening structure.

2.2.4 For `bolted in' units, hull receiving rings are to be of a material compatible with the hull. Scantlings of the receiving rings are to be as required by the jet unit manufacturer and suitably edge prepared prior to welding in place. The receiving ring is to be installed using an approved welding procedure. Where a manufacturer's specification is not provided, full details are to be submitted.

2.2.5 Bolt sizes and spacings are to be specified by the manufacturer, and are to be of suitable marine grade, insulated as appropriate and locked by suitable means.

2.2.6 Where studs are proposed for the receiving ring(s), the remaining thickness below the depth of blind tap is to be not less than the bottom shell plating thickness plus 2 mm. Bottoms of all blind taps are to be free of sharp corners.

2.2.7 The use of approved alignment resins may be considered where accurate seating and faying surfaces are required. Details are to be submitted for consideration and approval.

2.2.8 Where a water jet unit forms an integral part of the hull structure, such units are to be installed using an approved weld procedure and in accordance with the manufacturer's instructions. Materials to be welded are to be of compatible specifications.

2.2.9 Water jet units transmitting thrust into the transom structure are to be supported by a system of radial, athwartship and vertical stiffening. Drawings are to be accompanied by a set of detailed structural calculations. Where complex installations are proposed, a finite element model may be submitted in lieu of direct calculations.

2.2.10 Water jet units transmitting thrust to a bottom shell connection or intermediate tunnel connection are to be supported by additional stiffening, the details of which are to be submitted.

2.3.1 The materials and construction of the lifting surface will be considered on a case by case basis.

2.3.2 The design and performance of the lifting surface is outside the scope of classification. However, when submitting structural plans for the hull connection installation, the designer/Builder is to define:

1. Operating mode, i.e. fully submerged or surface piercing.

2. Maximum operational speed for which approval is sought.

3. Maximum, direct, bending, shear and torque loads generated by the foil at the point of attachment(s).

4. The type of profile or section used, e.g. N.A.C.A.

5. Supply of lift/drag profile.

6. If the foil is fixed, movable or retractable.

7. If the foil is fitted with control surfaces.

8. If the vertical leg(s) act as a rudder(s).

9. If shaft liners are carried to the foils at which support arrangements are provided.

10. If water intakes/scoops are fitted.

11. If propulsion units are fitted.

2.3.3 The scantlings and arrangements of foils and their supporting structure will require to be specially considered in the following cases where:

1. Propulsion units are incorporated within the foil.

2. Foils carry shaft support arrangements.

3. The foils are of novel design.

2.3.4 Where fully submerged foils are `built-in' to the hull, the attachment area is to be contained within a watertight compartment and the structural arrangements of Pt 7, Ch 5, 2.4 Surface drive mountings are to be complied with as appropriate.

2.3.5 Where foils are to be bolted to the structural foundation calculations are to be submitted to demonstrate that the effect of loading arising from high speed impact, grounding, fouling, etc. is limited to failure of the bolted connection. In all cases the structural and watertight integrity of the craft is to be maintained.

2.3.6 Attachment points of foils are to be contained within a watertight compartment.

2.3.7 Foils attached by riveted means are in addition to comply with Pt 7, Ch 2, 4.24 Butt straps.

2.3.8 Bow fairing doors fitted on forward retracting bow foils are to be weathertight and comply with Pt 3, Ch 4 Closing Arrangements and Outfit.

2.3.9 Aft bulkheads of bow foil compartments are to comply with the requirements for collision bulkheads as detailed in Pt 7, Ch 3, 7.7 Collision bulkheads.

2.3.10 Hydraulically operated retracting systems are to be equipped with low pressure and are to include a manual system of operation in the event of system failure.

2.3.11 A mechanical locking system is to be provided on retracting systems when the system is in both the operational and `stowed' conditions.

2.4.1 Transoms through which surface drive systems pass and which are required to carry thrust, significant weight, torque, moment, etc. are to be adequately reinforced.

2.4.2 The thickness of transom plating in way is to be not less than 1,5 times the thickness of the adjacent plating or as advised by the drive manufacturer, whichever is the greater.

2.4.3 Steering rams are to be mounted on suitably reinforced areas of plating supported by additional internal stiffening, details of which are to be submitted for consideration.

2.5.1 Sea inlet scoops may be integral with or an appendage to the hull.

2.5.2 Scoops are to be suitably positioned to minimise ventilation.

2.5.3 Suitable protective arrangements are to be provided to minimise the ingress of debris. The net area through the proposed arrangement is to be not less than twice that of the valves connected to the scoop. Provision is to be made for clearing the scoops by the use of suitable means and proposals are to be submitted.

2.5.4 Scoops are to be contained within a watertight compartment.

2.5.5 The plating thickness in way of integral scoops is to be not less than 1,5 times the thickness of the adjacent shell plating, with additional reinforcement at the leading edge.

2.5.6 For craft navigating in ice, the arrangements will be specially considered on an individual basis.

2.6.1 Where a vessel has been assigned a special features class notation associated with lifting appliances, the applicable lifting appliances are to be built in accordance with the requirements of LR’s Code for Lifting Appliances in a Marine Environment, July 2022.

2.6.2 It is the responsibility of the designer to ensure that the ship is suitable for the intended lifting appliance operations. Particular attention is drawn to ships or units which have:

1. been assigned the class notation LA; or
2. heavy lift cranes (or lifting appliances) installed (see Ch 4, 1.2 Lifting appliances and crane types 1.2.1.(k) of the Code for Lifting Appliances in a Marine Environment, July 2022).

2.6.3 Lifting appliance pedestals and foundations that are welded to the supporting hull structures are classification items, and the scantlings and arrangements are to comply with LR's requirements whether or not LR is also requested to certify or class the lifting appliance and issue the Register of Ship’s Lifting Appliances and Cargo Handling Gear, see Figure 5.2.1 Classification items and applicability of LR’s requirements for lifting appliance pedestals and foundations.

Figure 5.2.1 Classification items and applicability of LR’s requirements for lifting appliance pedestals and foundations

2.6.4 The design loads applied to the lifting appliance pedestals and foundations (such as masts, derrick posts and crane pedestals) are to comply with the requirements of LR's Code for Lifting Appliances in a Marine Environment, July 2022, see Figure 5.2.1 Classification items and applicability of LR’s requirements for lifting appliance pedestals and foundations.

2.6.5 Stowage arrangements are to be taken into account when calculating the loads applied to the pedestal.

2.6.6 When submitting plans for the proposed pedestal and foundation, the designer is to include design calculations covering the parameters indicated in Pt 7, Ch 5, 2.6 Lifting appliances and associated support arrangements 2.6.4 and Pt 7, Ch 5, 2.6 Lifting appliances and associated support arrangements 2.6.8.

2.6.7 Lifting appliance pedestals and foundations are to be efficiently supported and, in general, are to be carried through the deck and satisfactorily integrated into the surrounding structure. Alternatively, lifting appliance pedestals and foundations may be carried into a supporting structure of adequate strength, see Pt 7, Ch 5, 2.6 Lifting appliances and associated support arrangements 2.6.9. Proposals for other support arrangements will be specially considered.

2.6.8 The limiting stress coefficients for lifting appliance pedestals and foundation structural elements are given in Table 7.3.1 Limiting stress coefficients for local loading

2.6.9 The factored forces and moments resulting from aninstalled lifting appliance are to be taken into consideration on the basis of LR’s Code for Lifting Appliances in a Marine Environment, July 2022 when assessing the support arrangements, including the deck plating and underdeck stiffening in way of the lifting appliance pedestal and foundation. The global hull girder stresses are to be taken into account where applicable, with due consideration given to the material grade, see also Pt 7, Ch 6 Hull Girder Strength.

2.6.10 Insert plates are to be incorporated in the deck plating in way of lifting appliance foundations. The thickness of the insert plates is to be as required by the designer's calculations but is in no case is to be taken as less than 1,5 times the thickness of the adjacent attached plating.

2.6.11 All inserts are to have well radiused corners and be suitably edge prepared prior to welding. All welding in way is to be double continuous and full penetration where necessary. Tapers are to be not less than three to one.

2.6.12 The support arrangements for life-saving appliance davits and cranes are, in general, to be in accordance with Pt 3, Ch 9, 6.5 Support structure for life-saving appliances of the Rules and Regulations for the Classification of Ships, July 2022.

2.6.13 The support arrangements and scantlings of personnel handling (often called man-riding) appliances are to be in accordance with the requirements of LR's Code for Lifting Appliances in a Marine Environment, July 2022.

2.7.1 The design and scantlings of the skirt are outside the scope of classification, however the designer/builders are to submit their proposals in respect of the attachment detail. The following supporting information is to be submitted:

1. cushion pressure,

2. calculations demonstrating that the effect of damage to the flexible membrane and/or the retaining section arising from high speed impact, grounding, fouling, etc. will not compromise the structural and watertight integrity of the craft.

2.7.2 The skirt is to be securely attached around its periphery and is to be suitably reinforced by the use of backing plates.

2.7.3 Where the skirt is retained by bolting the retaining bars are to be as long as practicable with a fastener spacing of not more than 50 mm.

2.7.4 Where the design of the skirt is such that the flexible edge is retained by the use of a pre-formed channel, only the bolted hull connection of the preform to the hull structure is considered.

2.8.1 The shape, design and scantlings of the trim tabs are outside the scope of classification, however Clasifications Register (hereinafter referred to as 'LR') is concerned with their attachment to the hull structure.

2.8.2 The designer/Builder is to submit the following :

1. Detailed calculations indicating the maximum lift force generated by the tab for which acceptance is sought together with the corresponding speed and displacement.

2. Details and calculations of the hull attachment.

3. Details and calculations of the local internal reinforcement in way of the attachment.

2.8.3 Bearing materials used are to be of an approved type.

2.8.4 Fully submerged retractable trim tabs will be specially considered on a case by case basis.

2.9.1 Spray rails may be integrated into the hull structure or added in the form of an appendage on completion of the hull shell.

2.9.2 Where spray rails are integrated, they are to have a plating thickness not less than the adjacent bottom shell and additionally have a section modulus and inertia equivalent to that required for a longitudinal stiffener in the same position.

2.9.3 Where spray rails are added as an appendage, they are to be attached by double continuous welding and are additionally to comply with the strength requirements of Pt 7, Ch 5, 2.9 Spray rails 2.9.2.

2.9.4 Spray rails are to be supported by the internal stiffening arrangements and by additional local reinforcement as necessary.

2.9.5 In no case are the toes of spray rails to terminate on unsupported plating.

2.10.1 Other lifting surfaces not specifically covered by the Rules will be individually considered on the basis of submitted direct calculations.

2.10.2 Structure or hull shapes above the running waterline designed to generate aerodynamic lift may be individually considered on a case by case basis

2.10.3 Aerodynamic, hydrodynamic and aero-hydrodynamic stability are outside the scope of classification and are subject to the approval of the National Administration concerned.

2.11.1 Where propellers are fitted within ducts/tunnels the plating thickness in way of the blades is to be increased by 50 per cent.

2.11.2 The tunnel wall in way of the propeller blades is to be additionally stiffened.

2.12.1 Ducts penetrating the side inboard shell plating are to comply with the scantling requirements for side inboard structures, over their entire length in the appropriate material.

2.12.2 Ducts penetrating the wet deck are to comply with the scantling requirements for wet deck structures over their entire length in the appropriate material.

2.12.3 Open ends of ducts are to be fitted with a suitable protective grille.

2.12.4 The vent assembly, its design, construction and operation are outside the scope of classification and is the responsibility of the ride control system designer.

2.12.5 Details of the installation and securing arrangements of the vent valve assembly into the duct are to be submitted for approval.

2.13.1 The support structure (including hinges) in way of the interface between a ramp and the craft is to be assessed in accordance with the appropriate criteria given in Ch 6, 2 Loading and design criteria of the Code for Lifting Appliances in a Marine Environment, July 2022.

2.13.2 The loads that the ramp supporting structure will be subjected to are to be submitted by the designer or Shipbuilder. These loads are to be calculated in accordance with Ch 6, 2 Loading and design criteria of the Code for Lifting Appliances in a Marine Environment, July 2022. Load cases calculated in accordance with alternative standards can be accepted subject to agreement with LR.

2.13.3 Loads already existing in the supporting structure (other than those from the ramp) are to be superimposed if applicable.

2.13.4 Ramps forming part of the watertight integrity of the hull are also to be assessed in accordance with the applicable scantling requirements.