Section 5 Military design requirements

5.1.1 The strength of seats and supporting structure is to be sufficient to withstand the forces imposed by the equipment for all possible operating conditions and loads from ship motions, see Vol 1, Pt 5, Ch 3, 5.3 Pressure on internal decks, Pin. Design calculations are to be submitted.

5.1.2 The seating and supporting structure is to be tested in accordance with a specified standard, see also Vol 3, Pt 1, Ch 5, 3.1 General 3.1.4. Care is to be taken to ensure that the test arrangements represent the actual magnitude and direction of loads, and that the loading is applied to all relevant parts of the supporting structure rather than local items only.

5.1.3 Guidance on the loads and requirements for replenishment at sea operations are given in Vol 1, Pt 4, Ch 2, 9.2 Replenishment at sea loads

5.1.4 A sufficient deck area clear of projections and equipment suitably strengthened for impact loading is to be provided for the landing of stores and equipment.

5.1.5 RAS equipment is to be designed in accordance with a specified standard, see also Vol 3, Pt 1, Ch 5, 3.1 General 3.1.4.

5.2.1 The strength and stiffness of the holding down arrangements and the supporting structure under is to be sufficient to withstand the forces imposed by the vehicle(s) and or equipment for all possible operating conditions and loads from ship motions, see Vol 1, Pt 5, Ch 3, 5.3 Pressure on internal decks, Pin The design calculations are to be submitted.

5.3.1 Masts are to be of adequate strength and stiffness for the equipment they support. The design calculations are to be submitted.

5.3.2 Plated mast structure is to be treated as superstructure and the structural requirements for superstructure as defined in Table 3.3.9 Superstructure plating and Table 3.3.10 Superstructure framing in Pt 6, Ch 3 for NS1 type vessels and Vol 1, Pt 6, Ch 3, 4.8 Superstructures, deckhouses and bulwarks 4.8.4 and Vol 1, Pt 6, Ch 3, 4.8 Superstructures, deckhouses and bulwarks 4.8.5 for NS2 and NS3 type vessels are to be applied. Minimum requirements are given in Vol 1, Pt 6, Ch 3, 2 Minimum structural requirements and Vol 1, Pt 6, Ch 2, 2.9 Proportions of stiffener sections.

5.3.3 Pole mast structure is to be designed to be within the allowable stress limits defined in Vol 1, Pt 6, Ch 3, 16 Masts.

5.3.4 The excitation of the mast by ship motions, machinery, propellers and equipment is to be specially considered and the designers calculations are to be submitted. Where possible the designer should avoid mast natural frequencies within ±20 per cent of significant global mast excitation frequencies. Where this is not possible the vibration amplitudes should be calculated to confirm they are within acceptable limits for the mast structure and equipment. In general, ship motions can be estimated from Vol 1, Pt 5, Ch 3, 2 Motion response. See also Vol 1, Pt 6, Ch 2, 4 Vibration control. It is recommended that the frequency of the first mode of vibration of a pole mast be not less than 3,0 Hz to prevent potential excitation from the first vertical hull girder vibration mode in the range 1-2,5 Hz. The frequency of the first mode of vibration of a pole mast should be a minimum of 1 Hz above the first vertical hull girder mode.

5.3.5 Structure supporting radar or equipment critical to the operation of ship systems is to be of adequate stiffness to maintain the alignment of the equipment within the tolerance agreed with the manufacturer.

5.3.6 The mast should be designed and sited such that it produces minimum interference with the ships sensors and equipment.

5.3.7 Suitable permanent access arrangements are to be provided inside and on the exterior of the mast for maintenance of the structure and equipment. Provision is to be made for the drainage of water from all parts of the mast, both internal and external. Where applicable, protective coatings are to be applied in accordance with the requirements of Vol 1, Pt 6, Ch 6, 3.1 General. For corrosion margins, see Vol 1, Pt 6, Ch 6, 3.8 Corrosion margin.

5.3.8 Mast support arrangements are to be of suitable strength and stiffness and fully integrated into the hull or superstructure. The design calculations and arrangements are to be submitted.

5.3.9 For equipment distributed along the length of the ship, consideration is to be given to the global stiffness of the ships’ hull girder in relation to the alignment tolerances required for the equipment (increasing hull stiffness is not normally an efficient option).

5.3.10 High powered transmitting equipment where fitted is to be considered for the effects of electromagnetic influence on adjacent equipment and manned spaces.

5.4.1 The support structure of towed systems is to be suitably integrated into the main hull structure. Any additional primary stiffening is to be extended for at least three frame spaces forward and aft of the equipment.

5.4.2 The towing point and associated equipment is to be located over a primary longitudinal girder and preferably supported by a transverse web frame. The designers calculations are to be submitted for the supporting structure using the 1,5 times the maximum breaking load of the cable.

5.4.3 Towed array handling equipment is to be designed in accordance with a specified standard. The seating of array handling equipment is to be adequately supported.

5.5.1 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 1.5.1 Classification items and applicability of LR’s requirements for lifting appliance pedestals and foundations.

Figure 1.5.1 Classification items and applicability of LR’s requirements for lifting appliance pedestals and foundations

5.5.2 The scantlings of lifting appliance pedestals and foundations (such as masts, derrick posts and crane pedestals) are to be designed in accordance with a specified standard, with respect to the worst possible combinations of loads resulting from the installed lifting appliance self-weight, live load and accelerations, together with those resulting from the wind and the ship’s heel and trim, when in use and when stowed. When submitting plans for the proposed pedestal and foundation, the design calculations are to be included.

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

5.5.4 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 Vol 1, Pt 4, Ch 1, 5.5 Lifting appliances and support arrangements 5.5.6. Proposals for other support arrangements will be specially considered.

5.5.5 Deck plating and underdeck structure are to be reinforced under lifting appliance pedestals and foundations, and where the deck is penetrated the deck plating is to be suitably increased.

5.5.6 The forces and moments resulting from an installed lifting appliance are to be taken into consideration on the basis of the lifting appliance design standard 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 Vol 1, Pt 6, Ch 4 Hull Girder Strength.

5.5.7 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.

5.5.8 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.

5.5.9 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

5.5.10 Where life-saving appliance davits and cranes are used for additional military operations, the load cases are to be specially considered and the supporting deck structure assessed against these additional load cases. Consideration is to be given to the possibility of fatigue arising due to high cyclic loading.