Section 5 Definitions

5.1.1 The following definitions apply except where they are inappropriate or where specifically defined otherwise.

5.2.1  Length waterline, L _WL, is the distance, in metres, measured on a waterline at the design draught from the fore side of the stem to the after side of the stern or transom as shown in Figure 1.5.1 Lengths

5.2.2  Rule length, L _R, is the distance, in metres, on a waterline at the design draught from the forward side of the stem to the after side of the rudder post or to the centre of the rudder stock if there is no rudder post. L _R is to be not less than 96 per cent, and need not be greater than 97 per cent, of the extreme length on a waterline at the design draught. In vessels without rudders, the Rule length, L _R, is to be taken as 97 per cent of the extreme length on a waterline at the design draught. In vessels with unusual stem or stern arrangements, the Rule length will be specially considered.

5.2.3 All references to longitudinal locations in the Rules are to be taken as forward of the aft end of L _R unless otherwise stated, e.g. 0,75L _R is 75 per cent of L _R forward of the aft end of L _R.

5.2.4  Length between perpendiculars, L _PP, is the distance, in metres, on the waterline at the design draught from the forward to the after perpendicular.

5.2.5  Forward perpendicular, F.P., is the perpendicular at the intersection of the waterline at the design draught with the fore side of the stem.

5.2.6  After perpendicular, A.P., is the perpendicular at the intersection of the waterline at the design draught with the after side of the rudder post or to the centre of the rudder stock for vessels without a rudder post or to the intersection with the transom profile on the centreline.

5.2.7  Length overall, L _OA , is the distance, in metres, measured parallel to the deep load waterline from the fore side of the stem to the after side of the stern or transom, excluding rubbing strakes and other projections as shown in Figure 1.5.1 Lengths.

Figure 1.5.1 Lengths

5.2.8  Waterline breadth, B _WL, is generally the greatest moulded breadth, in metres, measured at the design draught, as shown in Figure 1.5.2 Tranverse dimensions.

Figure 1.5.2 Tranverse dimensions

5.2.9  Breadth, B, is generally the greatest moulded breadth, in metres, throughout the depth of the ship or as defined in appropriate Chapters. For vessels of unusual cross-section the breadth will be specially considered.

5.2.10  Depth, D, is measured, in metres, at amidships, from top of keel plate to the moulded deck line at side on the uppermost continuous deck, or as defined in appropriate Chapters or standards. When a rounded gunwale is arranged, the depth D is to be measured to the continuation of the moulded deck line at side.

5.2.11  Draught, T, is the design draught, in metres, measured from moulded baseline.

5.2.12  Block coefficient, C _b , is the block coefficient at draught T corresponding to a waterline at the design draught, based on Rule length L _R and breadth B _WL, as follows:

C b

=

5.2.13 Design draught (scantling draught) is measured from the waterline when the vessel is in the deep draught condition plus any specified design, build or Owners margins, see Vol 1, Pt 3, Ch 1, 5.3 Margins. Where specified, a higher waterline may be used for any temporary operational conditions exceeding the design draught, for example a docked down condition.

5.2.14 Deep draught is measured at a displacement such that the ship is in all respects complete, and is fully loaded with full complement, stores, fuel, water and payload plus any specified growth margin, see Vol 1, Pt 3, Ch 1, 5.3 Margins. A deep operational draught may be defined for machinery trials and performance measurement where the deep draught is unachievable at the start of life. Where a vessel has an assigned load line, the deep draught is not to be less than the summer load line draught.

5.2.15 Payload is the equipment and stores that are carried by the vessel for the purposes of fulfilling its operational requirements.

5.3.1 Design margin is an allowance for uncertainties used in the estimation of weight for design purposes.

5.3.2 Build margin is an allowance for unforeseen changes that may need to be made by the builder of the vessel.

5.3.3 Owners margin is an allowance to cater for modifications made by the Owner to the vessel or equipment during the design and build stages.

5.3.4 Growth margin is an allowance for future controlled and uncontrolled weight growth over the design life of the ship.

5.3.5 In the absence of any specific requirements, the sum of the margins is be taken as 15 per cent of the displacement at the deep draught.

5.4.1 Strength deck is normally the uppermost continuous deck. Other decks may be considered as the strength deck provided that such decks are structurally effective. Where the upper deck is stepped, as in the case of vessels with a quarter deck, the strength deck is stepped, see Vol 1, Pt 6, Ch 4, 1 General.

5.4.2 The weather deck is generally the lowest continuous deck exposed to sea and weather loads. It is to be defined at the early stages of design in conjunction with LR and the Builder.

5.4.3 Other decks that are exposed to sea loads are to be assessed in accordance with the requirements for weather decks.

5.4.4 The damage control deck is the lowest deck on which continuous fore and aft access is provided to aid communications and recovery following damage. It is normally located above the lowest vertical limit of watertight integrity at the centreline, the exact location being determined by the relevant sub-division and watertight integrity standard.

5.5.1 Unless otherwise stated, the co-ordinate system is as shown in Figure 1.5.3 NSR Co-ordinate system, that is, a right-hand co-ordinate system with the X axis positive forward, the Y axis positive to port and the Z axis positive upwards. Angular motions are considered positive in a clockwise direction about the X, Y or Z axes.

5.6.1 For the purposes of strength assessment a superstructure is defined as a decked structure on the strength deck, extending from side to side of the vessel, or with its side plating being less than four per cent of the breadth, B, inboard of the shell plating.

Figure 1.5.3 NSR Co-ordinate system

5.7.1 A deckhouse is in general defined as a decked structure on or above the strength deck with its side plating being four per cent or more of the breadth, B, inboard of the shell plating.

5.8.1 A boundary or closing appliance is considered weathertight if it is capable of preventing the passage of water into the ship in any sea conditions.

5.9.1 A boundary or closing appliance is considered watertight if it is capable of preventing the passage of water in either direction under a head of water for which the surrounding structure is designed.

5.10.1  Figure 1.5.4 Longitudinal framing system shows the general terminology adopted for structural items for a longitudinally framed ship.

5.10.2 Vol 1, Pt 3, Ch 1, 5.10 Terminology 5.10.3 shows the general terminology adopted for structural items for a transversely framed ship.

5.10.3  Figure 1.5.6 NS1 Conventional aircraft carrier shows the general configuration of Naval ships of the NS1 and NS2 types. Various features are pointed out and are dealt with by the relevant Section of the Rules.

Figure 1.5.4 Longitudinal framing system

Figure 1.5.5 Transverse framing system

Figure 1.5.6 NS1 Conventional aircraft carrier

Figure 1.5.7 NS1 Short take off aircraft carrier

Figure 1.5.8 NS2 Frigate/Destroyer

5.11.1 The minimum extent of watertight subdivision (internal), and integrity (internal and external), is to be in accordance with the specified subdivision and stability standard(s).

5.11.2 The minimum extent of watertight subdivision may be defined by a combination of decks, side shell and bulkheads or by a single deck.

5.11.3 Weathertight and watertight fittings and closing appliances are to be fitted in accordance with the requirements of the boundary on which they are placed.

5.11.4 For the calculation of watertight structural scantlings the pressure head is to be taken from the vertical limits of weathertightness determined by either intact or damage stability considerations in accordance with the specified subdivision and stability standard(s), see Vol 1, Pt 3, Ch 2, 1.3 Watertight and weathertight integrity and Vol 1, Pt 5, Ch 3, 5.5 Loads for deckhouses, bulwarks and superstructures, Pdh

5.12.1 A critical compartment is one which, at battle stations, contains equipment or personnel without whom functions critical to combat survivability would be lost. These functions include the ability to fight, manoeuvre or communicate.

5.12.2 Critical compartments are typically the chart room, operations room, conning position, ship’s control room and main communications office. Other compartments may be considered critical depending on ship’s layout and design. The need for protecting critical compartments can be reduced by avoiding single point failure nodes and by concentrating and protecting those which cannot be avoided. A vulnerability analysis can be used to identify vulnerable critical compartments and the essential pieces of equipment or systems that are required to be protected, see Vol 1, Pt 3, Ch 1, 2.2 Submission of direct calculations.

5.12.3 Critical pipe and cable runs are routes in which the connections for survivability critical components run. They can cover individual routes or concentrated areas. An example is a run containing wave guides and signal cables for all the above water sensors on the mast.

5.13.1 Unless otherwise stated, the variables used in the Rules are expressed in the following units.

5.13.2  General

5.13.3  Hull girder properties

5.13.4  Stiffeners

5.13.5  Plating

5.13.6  Loads

5.13.7  Other items