Section 2 Rig calculation requirements

2.1.1 Appropriate rig materials are selected by the designer. Modelling and assessment are done using techniques corresponding to the material of rig element.

2.1.2 Composite material is non-isotropic. Mid-plane methods may be used for global evaluation of in-plane stress in cases with balanced fibre layup. Any load transfer through the thickness of the material is to be considered to be carried by the matrix material only. The difference between the strength of the matrix material and the strength of the fibres is to be taken into account.

2.1.3 Metallic materials are isotropic but analysis is to be done using thin walled sections where appropriate and geometric accurate volume models where possible.

2.1.4 The analysis shall account for the load factors with respect to potential failures through global buckling, shear stiffness of spar tubes, thin-wall buckling, and other stability evaluations used in the design process.

2.1.5 Results are to be represented in a phenomenological material failure index such as the Tsai-Wu failure criterion. Individual component failure index values for compressive, tensile and shear strength are not considered suitable for evaluation.

2.2.1 Sailing condition load cases are to be applied to the rig. Reference is made to LR’s Guidance Notes for the Certification of Masts, Spars and Standing Rigging, January 2017 for a minimal set of requirements when determining these loads.

2.2.2 All load cases are to be identified with a load case number.

2.2.3 Load cases that cover operation at sea are to include sails set, limiting wind and sea conditions with corresponding angle of heel and wind direction. A reefed storm condition may need to be considered depending on the operational profile of the craft.

Load case assumptions are to be checked against handling procedures.

2.2.5 Loads in the survival condition are to be based on:

1. Motions estimated from model tests or computation. In the absence thereof, accelerations and amplitudes given in Table 7.2.1 Motions may be applied.
2. Wind speed of 63 m/s is to be assumed.

Table 7.2.1 Motions

Motion	Maximum single amplitude	Period in seconds
Roll	Φ = sin-1 θ degrees but need not exceed 30° and is not to be taken less than 22°.
Pitch	Ψ = 12e-0,0033Lpp degrees but need not exceed 8°.
Heave
Where Lpp, B as defined in Pt 3, Ch 1, 6.2 Principal particulars GM transverse metacentric height of loaded craft, in metres

2.2.6 Dynamic loads in sailing conditions are to be determined from simulations or other established computation techniques. In the absence of this information, an allowance for dynamic loads by a multiplication factor of 1,33 on the combination of load by wind and own weight is to be taken.

2.2.7 If the operational envelope includes the risk of ice build-up, the weight of ice is to be taken into account in all relevant load cases. Ice build-up includes an additional risk of hindering operation of control systems, and provisions are to be made to mitigate the risk of failure of the rig in these conditions.

2.3.1 The stress factors given in this Section are related to the Characteristic Failure Stress (CFS), minimum 0,2 per cent proof stress and minimum yield strength. The CFS is the stress at which, for the material loaded in the way it is loaded in the rig structure, the probability of breakage does not exceed 5 per cent.

For composite materials, the CFS to be used for scantling calculation purposes is to be 90 per cent of the mean first ply/resin cracking failure determined from accepted mechanical tests, or the mean values minus two times the standard deviation of not less than 5 representative samples, whichever is the lesser. All test pieces are to be representative of the product to be manufactured and details of them are to be submitted for consideration.

2.3.3 Permissible stress for aluminium materials is:

• Permissible stress = SF σ_a

2.3.4 Permissible stress for steel materials is:

• Permissible stress = SF σ_s

2.3.5 Stress factors (SF) are related to modes of operation (seagoing, survival) and are given in Table 7.2.2 Stress factors (SF) for seagoing and survival conditions.

Table 7.2.2 Stress factors (SF) for seagoing and survival conditions

Condition	Metal	Composite
Controlled condition during manufacture/stepping/maintenance	0,80	0,33
Masts and spars in sailing condition	0,65	0,25
Masts and spars in survival condition	0,80	0,33
Standing rigging in sailing condition	0,53	0,27 (carbon) 0,37 (PBO)
Standing rigging in survival condition	0,68	0,34 (carbon) 0,47 (PBO)
Note 1. If a significant part of the load under consideration is a personnel load, then the stress factor is not to exceed 0,4 for metal or 0,17 for a composite material. Note 2. For masts and spars, the stress factors are valid for both tensile and compression load types. Proposals to use a separate factor for compression will be subject to special consideration. Note 3. Where an element is subjected to a combined load, such as bending and compression, this combination is also to be considered using Where: σb is the bending stress in the mast section under consideration σy is the tensile yield stress for the material σa is the axial stress in the mast section under consideration σc is the critical buckling for the mast section Other materials will be specially considered. See also Pt 3, Ch 7, 2.1 Modelling of the rig elements 2.1.3. Note 4. Stress factors for other sailing conditions are to be agreed with LR in the load case definition phase. Note 5. For composite materials, see Pt 8, Ch 1, 2.5 Materials data sheet.