Section 2 Materials

2.1.1 The materials used in the construction of the craft are to be manufactured and tested in accordance with the appropriate requirements of Ch 3 Rolled Steel Plates, Strip, Sections and Bars of the Rules for the Manufacture, Testing and Certification of Materials (hereinafter referred to as the Rules for Materials.

2.1.2 All materials are to be manufactured at works which have been approved by LR for the type and, where appropriate, grade of steel which is being supplied and for the relevant steel production and processing route.

2.2.1 The grade of steel, supply condition and its mechanical properties are to be indicated on the construction plans.

2.2.2 When plate material, intended for welded construction, will be subject to significant strains in a direction perpendicular to the rolled surfaces, it is recommended that consideration be given to the use of special plate material with specified through thickness properties, and tested in accordance with Ch 3, 8 Plates with specified through thickness properties of the Rule for Materials.

2.3.1 Where steel castings or forgings are used for sternframes, rudder frames, rudder stocks, propeller shaft brackets and other major structural items, they are to comply with Pt 6, Ch 4 Scantling Determination for Multi-Hull Craft or Pt 6, Ch 5 Special Features, as appropriate.

2.4.1 The scantlings determined within this Part of the Rules assume that mild steel has the following mechanical properties:

2.4.2 Steel having a specified minimum yield stress of 235 N/mm² (24 kgf/mm²) is regarded as mild steel. Steel having a higher specified minimum yield stress is regarded as higher tensile steel.

2.4.3 The requirements for global strength considerations in craft incorporating higher tensile steel materials are to be based on a higher tensile steel concentration factor, η_HTS, as given in Table 2.2.1 Higher tensile steel concentration factor η_HTS .

2.4.4 The local scantling requirements of higher tensile steel plating, longitudinals, stiffeners and girders may be based on a k _s factor determined as follows:

or 0,66 whichever is the greater

2.4.5 For the application of the requirements of Pt 6, Ch 2, 2.4 Mechanical properties for design 2.4.3 and Pt 6, Ch 2, 2.4 Mechanical properties for design 2.4.4 special consideration will be given to steel where σ_s > 355 N/mm². Where such steel grades are used in areas which are subject to fatigue loading the structural details are to be verified using fatigue design assessment methods.

2.5.1 Corrosion prevention requirements are to be in accordance with Chapter 15 of the Rules for Materials.

2.5.2 All steelwork, except inside integral fuel tanks, is to be suitably protected against corrosion. This may be by coating or, where applicable, by a system of cathodic protection.

2.5.3 Steelwork is to be suitably cleaned and cleared of millscale before the application of any coating. It is recommended that blast cleaning, or other equally effective means, be employed for this purpose.

2.5.4 Where a cathodic protection system is fitted, plans showing the proposed layout of anodes and hull penetrations are submitted in accordance with Ch 15 Corrosion Prevention of the Rules for Materials.

2.6.1 The hull is to be protected against corrosion by a suitable protective coating.

2.6.2 Prefabrication primers are to be approved in accordance with Ch 15 Corrosion Prevention of the Rules for Materials.

2.6.3 Paints or other coatings are to be suitable for the intended purpose in the locations where they are to be used, and where appropriate, approved in accordance with Ch 15 Corrosion Prevention of the Rules for Materials. Coatings are to be of adequate film thickness, applied in accordance with the paint manufacturer’s specification.

2.6.4 Integral fuel tanks are to be cleaned and dried, after testing, and then treated with a suitable coating, in accordance with the manufacturer's recommendations.

2.6.5 Paints, varnishes and similar preparations having a nitro-cellulous or other highly flammable base are not to be used in accommodation or machinery spaces.

2.7.1 Where bimetallic connections are made, involving dissimilar metals, measures are to be incorporated to preclude galvanic corrosion. In order to prevent galvanic corrosion, special attention is to be given to the penetrations of, and connections to the hull, bulkheads and decks by piping and equipment where dissimilar materials are involved.

2.8.1 The design shall ensure that the location of all bimetallic connections allows for regular inspection and maintenance of the joints and penetrations during service.

2.9.1 For the deferment of dry-docking or where an IWS (In-Water Survey) notation is to be assigned protection of the underwater portion of the hull is to be provided by means of a suitable high resistance paint applied in accordance with the manufacturer's requirements. Details of the high resistance paint are to be submitted for information.

2.10.1 Where an impressed current cathodic protection (ICCP) system is fitted, plans showing the proposed layout of anodes, reference cells, wiring diagram and the means of bonding-in of the rudder and propeller, are to be submitted. ICCP requirements are to be in accordance with Ch 15 Corrosion Prevention of the Rules for Materials.

2.10.2 The arrangement for glands, where cables pass through the shell, are to include a small cofferdam. Cables to anodes are not to be led through tanks containing low flash point oils.

2.11.1 Cathodic protection may be used in association with coatings for the protection of ballast spaces, see Ch 15 Corrosion Prevention of the Rules for Materials.

2.11.2 The anodes are to be of approved design and sufficiently rigid to avoid resonance in the anode support. Steel cores are to be fitted, and these are to be so designed as to retain the anode even when the latter is wasted.

2.11.3 Anodes are to be attached to the structure in such a way that they remain secure both initially and during service. The following methods of attachment would be acceptable:

1. Steel core connected to the structure by continuous welding of adequate section.

2. Steel core bolted to separate supports, provided that a minimum of two bolts with lock nuts are used at each support. The separate supports are to be connected to the structure by continuous welding of adequate section.

3. Approved means of mechanical clamping.

2.11.4 Anodes are to be attached to stiffeners, or may be aligned in way of stiffeners on plane bulkhead plating, but they are not to be attached to the shell. The two ends are not to be attached to separate members which are capable of relative movement.

2.11.5 Where cores or supports are welded to the main structure, they are to be kept clear of the toes of brackets and similar stress raisers. Where they are welded to asymmetrical stiffeners, they are to be connected to the web with the welding kept at least 25 mm away from the edge of the web. In the case of stiffeners or girders with symmetrical face plates, the connection may be made to the web or to the centreline of the face plate but well clear of the free edges. However, it is recommended that anodes are not fitted to face plates of higher tensile steel longitudinals.

2.12.1 Where plated decks are sheathed with wood, the sheathing is to be efficiently attached to the deck, caulked and sealed, to the satisfaction of the Surveyor in accordance with the approved drawings.

2.12.2 Deck coverings in the following positions are to be of a type which will not readily ignite when used on decks:

1. Forming the crown of machinery or cargo spaces within accommodation spaces of cargo craft.

2. Within accommodation spaces, control stations, stairways and corridors of passenger craft.

2.13.1 The scantlings determined from the formulae provided in the Rules assume that the materials used are selected, manufactured and protected in such a way that there is negligible loss in strength by corrosion.

2.13.2 Where steel is not protected against corrosion by painting or other approved means, further consideration of the scantlings is required.

2.14.1 Construction procedures, materials and welding are to be in accordance with the requirements of this Chapter such that stress corrosion cracking is avoided.

2.14.2 High local stresses are to be avoided by the use of suitable design detail. See also LR's Guidance Notes for Structural Details.

2.14.3 The resistance to fracture is controlled, in part, by the notch toughness of the steel used in the structure. Steels with different levels of notch toughness are specified in Rules for the Manufacture, Testing and Certification of Materials, July 2022. The grade of steel to be used is, in general, related to the thickness of the material and the stress pattern associated with its location.

2.14.4 Where tee or cruciform connections employ full penetration welds, and the plate material is subject to significant strains in a direction perpendicular to the rolled surfaces, it is recommended that consideration be given to the use of special plate material with specified through thickness properties, as detailed in Ch 3, 8 Plates with specified through thickness propertiesof the Rules for Materials.

2.14.5 For craft operating for long periods in low air temperature the material of exposed structures will, in general, be specially considered.