Section 7 Bulkheads and deep tanks

7.1.1 The requirements of this Section apply to craft with bulkheads of either sandwich or single skin composite construction.

7.1.2 Watertight and collision bulkheads are to be fitted in accordance with the requirements of Pt 3, Ch 2, 4 Bulkhead arrangements.

7.1.3 FRP composite bulkheads and plywood bulkheads are, where practicable, to be suitably attached to receiving frames, see also LR's Guidance Notes for Structural Details. The bulkheads are to be attached using double angles or equivalent, see Pt 8, Ch 3, 1.19 Boundary bonding. Proposals to fit bulkheads and tank boundaries on receiving strips in lieu of frames, will be individually considered.

7.1.4 Where bulkheads are of steel or aluminium construction, their scantlings and arrangements are to be in accordance with Pt 6, Ch 3 Scantling Determination for Mono-Hull Craft or Pt 7, Ch 3 Scantling Determination for Mono-Hull Craft respectively. The method of attachment to the framing will be specially considered.

7.1.5 For bulkheads in way of partially filled holds or tanks, sloshing forces may be required to be taken into account. Where such forces are likely to be significant, the scantlings will be required to be verified by additional calculations which are to be submitted with the plans.

7.1.6 In deep tanks which extend from side to side a centreline bulkhead is generally to be fitted. The bulkhead may be intact or perforated as desired. If intact the scantlings are to comply with the requirements of Pt 8, Ch 3, 7.4 Deep tanks and Pt 8, Ch 3, 7.11 Wash plates for tank boundary bulkheads. If perforated, they are to comply with the requirements of Pt 8, Ch 3, 7.11 Wash plates for washplates.

7.1.7 The scantlings of non-watertight or partial bulkheads are, in general, to be as required by Pt 8, Ch 3, 7.3 Watertight bulkheads for watertight bulkheads. Non-watertight or partial bulkheads supporting hull framing are to have scantlings equivalent to frames or web frames, in the same position, as appropriate.

7.2.1 The symbols and definitions for use within this Section are as given in Pt 8, Ch 3, 1.5 Symbols and definitions 1.5.1.

7.3.1 Composite watertight bulkheads may be of sandwich construction, with or without stiffeners, or of single skin construction with closely spaced vertical or horizontal stiffeners. Where steel or aluminium alloy bulkheads are fitted, their scantlings and arrangements are to be in accordance with Pt 6, Ch 3 Scantling Determination for Mono-Hull Craft or Pt 7, Ch 3 Scantling Determination for Mono-Hull Craft respectively. Sandwich timber bulkheads, plywood bulkheads or other forms of bulkhead construction will be considered on the basis of equivalent strength and stiffness. Where bulkheads are of novel design they will be specially considered.

7.3.2 The bending moment assumed to be carried by the watertight bulkhead plating is to be not less than that determined from Pt 8, Ch 3, 1.9 Plate and sandwich laminates 1.9.1, using the design pressure from Pt 5, Ch 3, 3.1 Hull structures for both non-displacement or displacement type craft. This bending moment is to be applied to laminates of both single skin and sandwich construction in the determination of the panel scantling required by Pt 8, Ch 3, 7.3 Watertight bulkheads 7.3.3 and Pt 8, Ch 3, 7.3 Watertight bulkheads 7.3.5 respectively.

7.3.3 An estimate of the thickness of watertight bulkhead single skin plating is to be determined from Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.1. The tensile and compressive stresses are to be determined for each ply of reinforcement in the proposed laminate using Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.3 and Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.4, see also LR's Guidance Notes for Calculation Procedures for Composite Construction. The allowable tensile and compressive stress limits indicated in Table 7.3.1 Limiting stress criteria for local loading are to be complied with.

7.3.4 In no case is the minimum thickness of single skin plating to be taken as less than 2,5 mm.

7.3.5 An estimate of the stiffness E , thickness of single skin plating for outer and inner skins of the bulkhead sandwich panel and the thickness of core material is to be determined from Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.2 and Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.9 respectively. The tensile and compressive stresses are to be determined for each ply of reinforcement in the proposed laminate using Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.7 and Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.8. The allowable tensile and compressive stress limits indicated in Table 7.3.1 Limiting stress criteria for local loading are to be complied with.

7.3.6 The amount of reinforcement in laminates that form the skins of a sandwich laminate is to comply with the requirements of Pt 8, Ch 3, 2.5 Minimum skin reinforcement in sandwich laminates 2.5.1.

7.3.7 Special consideration may be given to laminate thicknesses lesser than that required by Pt 8, Ch 3, 7.3 Watertight bulkheads 7.3.4 and Pt 8, Ch 3, 7.3 Watertight bulkheads 7.3.6, provided that all of the structural strength requirements of the Rules are complied with, a satisfactory water barrier is provided, see Pt 8, Ch 3, 2.3 Sandwich skin laminate 2.3.1, and the equivalent impact resistance is demonstrated as required by Pt 8, Ch 3, 2.8 Impact considerations 2.8.2.

7.3.8 The Rule requirements for bending moment, shear force, shear stress and deflection for the bulkhead stiffeners are to be determined from the general equations given in Pt 8, Ch 3, 1.15 Stiffeners general, using the design pressure from Pt 5, Ch 3, 3.1 Hull structures for both non-displacement or displacement type craft, and the coefficients Φ_M, Φ_S and Φ_δ as indicated in Table 3.1.10 Shear force, bending moment and deflection coefficients for the appropriate load model.

7.3.9 The allowable tensile, compressive and shear stress limits indicated in Table 7.3.1 Limiting stress criteria for local loading , and the span/deflection ratios indicated in Table 7.2.1 Limiting span/deflection ratio are to be complied with.

7.3.10 The geometric properties of stiffener sections are to be calculated in accordance with Pt 8, Ch 3, 1.16 Geometric properties stiffener sections using an effective width of attached plating as indicated in Pt 8, Ch 3, 1.7 Effective width of attached plating.

7.3.11 Bulkheads are to be suitably strengthened, if necessary, at the ends of deck girders and where subjected to concentrated loads.

7.3.12 Bulkheads in engine rooms that may be exposed to fuel oils are to be suitably protected against damage by fuel oil and by fire, see Pt 8, Ch 3, 7.15 Fire protection.

7.4.1 Composite integral/deep tank bulkheads may be of sandwich construction with or without stiffeners, or of single skin with closely spaced vertical or horizontal stiffeners. Where steel or aluminium alloy integral/deep tank bulkheads are fitted, their scantlings and arrangements are to be in accordance with Pt 6, Ch 3 Scantling Determination for Mono-Hull Craft or Pt 7, Ch 3 Scantling Determination for Mono-Hull Craft respectively. Other forms of bulkhead construction will be considered on the basis of equivalent strength and stiffness. Where bulkheads are of novel design they will be specially considered.

7.4.2 A centreline bulkhead is, generally, to be fitted in deep tanks which extend from side to side of the craft. The bulkhead may be intact or perforated as desired. If intact, the plate scantlings are to be as required for boundary bulkheads.

7.4.3 The bending moment, M _b or M _c, as appropriate, assumed to be carried by the integral/deep tank bulkhead plating is to be not less than that determined from Pt 8, Ch 3, 1.9 Plate and sandwich laminates 1.9.1, using the design pressure from Pt 5, Ch 3, 3.1 Hull structures for both non-displacement or displacement type craft. This bending moment is to be applied to laminates of both single skin and sandwich construction in the determination of the panel scantling required by Pt 8, Ch 3, 7.4 Deep tanks 7.4.4 and Pt 8, Ch 3, 7.4 Deep tanks 7.4.6 respectively.

7.4.4 An estimate of the thickness of integral/deep tank bulkhead single skin plating is to be determined from Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.1. The tensile and compressive stresses are to be determined for each ply of reinforcement in the proposed laminate using Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.3 and Pt 8, Ch 3, 1.13 Determination of properties and stresses for single skin plate laminates 1.13.4. The allowable tensile and compressive stress limits indicated in Table 7.3.1 Limiting stress criteria for local loading are to be complied with.

7.4.5 In no case is the minimum thickness of single skin plating to be taken as less than 4,5 mm.

7.4.6 An estimate of the stiffness E , thickness of single skin plating for outer and inner skins of integral/deep tank bulkhead sandwich panels and the thickness of core material is to be determined from Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.2 and Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.9 respectively. The tensile and compressive stresses are to be determined for each ply of reinforcement in the proposed laminate using Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.7 and Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.8. The allowable tensile and compressive stress limits indicated in Table 7.3.1 Limiting stress criteria for local loading are to be complied with.

7.4.7 The amount of reinforcement in laminates that form the skins of a sandwich laminate is to comply with the requirements of Pt 8, Ch 3, 2.5 Minimum skin reinforcement in sandwich laminates 2.5.1, see Pt 8, Ch 3, 2.6 Integral tank structure 2.6.2.

7.4.8 Special consideration may be given to laminate thicknesses less than that required by Pt 8, Ch 3, 7.4 Deep tanks 7.4.5 and Pt 8, Ch 3, 7.4 Deep tanks 7.4.7, provided that all of the structural strength requirements of the Rules are complied with, a satisfactory water barrier is provided, see Pt 8, Ch 3, 2.3 Sandwich skin laminate 2.3.1, and the equivalent impact resistance is demonstrated as required by Pt 8, Ch 3, 2.8 Impact considerations 2.8.2.

7.4.9 The Rule requirements for bending moment, shear force, shear stress and deflection for the integral/deep tank stiffeners are to be determined from the general equations given in Pt 8, Ch 3, 1.15 Stiffeners general, using the design pressure from Pt 5, Ch 3, 3.1 Hull structures for both non-displacement or displacement type craft, and the coefficients Φ_M, Φ_S and Φ_δ as indicated in Table 3.1.10 Shear force, bending moment and deflection coefficients for the load model (a).

7.4.10 The allowable tensile, compressive and shear stress limits indicated in Table 7.3.1 Limiting stress criteria for local loading , and the span/deflection ratios indicated in Table 7.2.1 Limiting span/deflection ratio are to be complied with.

7.4.11 The geometric properties of stiffener sections are to be calculated in accordance with Pt 8, Ch 3, 1.16 Geometric properties stiffener sections using an effective width of attached plating as indicated in Pt 8, Ch 3, 1.7 Effective width of attached plating.

7.4.12 Integral/deep tank bulkheads are to be suitably strengthened, if necessary, at the ends of deck girders and where subjected to concentrated loads.

7.4.13 Integral/deep tank bulkheads in engine rooms that may be subjected to fuel oils are to be suitably protected against damage by fuel oil and by fire, see Pt 8, Ch 3, 7.15 Fire protection.

7.5.1 The scantlings of double bottom tanks are to meet the structural requirements for deep tanks in accordance with Pt 8, Ch 3, 7.4 Deep tanks.

7.5.2 Where the crown of a double bottom tank forms a vehicle, passenger or other deck, the requirements of Pt 8, Ch 3, 8 Deck Structures are also to be complied with.

7.6.1 The scantlings of composite collision bulkheads are to meet the requirements of Pt 8, Ch 3, 7.3 Watertight bulkheads but with allowable tensile, compressive and shear stress limits for collision bulkheads as indicated in Table 7.3.1 Limiting stress criteria for local loading in Chapter 7.

7.6.2 If the collision bulkhead forms the boundary of a deep tank or cofferdam the requirements of Pt 8, Ch 3, 7.4 Deep tanks are to be complied with.

7.7.1 Where gastight bulkheads are fitted, in accordance with Pt 3, Ch 2, 4 Bulkhead arrangements, their scantlings are to be as required for watertight bulkheads.

7.7.2 Gastight bulkheads are to be fitted to protect accommodation spaces from gases and vapour fumes from machinery, exhaust and fuel systems.

7.8.1 Plywood used for bulkheads is to be high quality marine plywood, and is to be in accordance with the requirements of Pt 8, Ch 2, 2.17 Plywood.

7.8.2 The structural requirements of plywood watertight bulkheads are to be as required by Pt 8, Ch 3, 7.1 General.

7.9.1 Where a bulkhead is structural but non-watertight, the scantlings are, in general, to be as required for watertight bulkheads or equivalent in strength to web frames in the same position. Partial bulkheads that are non-structural are outside the scope of LR classification.

7.10.1 Primary longitudinal stiffening members are to be continuous through transverse bulkheads.

7.10.2 Where a stiffener passes through a watertight bulkhead the bonding of the stiffener and compensation in way is to be not less than the laminate weight of the bulkhead.

7.10.3 Where structural members pass through the boundaries of watertight bulkheads or integral/deep tanks, and leakage into the adjacent space could be hazardous or undesirable, suitable cofferdams are to be built into the cores of top-hat stiffeners on each side of the boundary. The minimum thickness of such cofferdams is 4,5 mm.

7.10.4 Pipe or cable runs through watertight bulkheads are to be fitted with suitable watertight glands.

7.11.1 Tanks are to be subdivided as necessary by internal baffles or wash plates and the minimum thickness of the laminate for any internal structure is not, in general, to be less than 4,5 mm at a fibre content of 0,5 or equivalent thickness. Baffles or wash plates which support hull framing are to have scantlings equivalent to web frames in the same position.

7.11.2 Wash plates and wash bulkheads are, in general, to have an area of perforation not less than 10 per cent of the total area of the bulkhead. The perforations are to be so arranged that the efficiency of the bulkhead as a support is not impaired.

7.11.3 The plate thickness is to be not less than the structural element from which the wash bulkhead is formed.

7.12.1 A cofferdam is to be fitted between fresh water and fuel oil or sanitary tanks. The scantlings of cofferdams are to comply with the requirements for deep tank bulkheads given in Pt 8, Ch 3, 7.4 Deep tanks.

7.13.1 Fuel tanks are to incorporate a resin rich surface or be coated with an oil retardant resin on the internal exposed surfaces. Potable fresh water tanks are similarly to be coated with a suitable non-tainting resin.

7.14.1 Air pipes sufficient in number and area are to be fitted to each tank in accordance with Pt 15, Ch 2, 11 Air, overflow and sounding pipes.

7.15.1 Fire protection requirements as given in Pt 17 Fire Protection, Detection and Extinction are to be complied with.

7.16.1 All compartments within the craft are to be accessible in order to facilitate proper maintenance and future structural surveys. Linings on craft-sides, deck-heads and bulkheads etc. must be capable of being removed. Similarly, sufficient space must be available below lower decks/soles to provide proper access to the bottom structure; an adequate number of manholes, removable panels, etc. are to be provided for this purpose.

7.16.2 Doors fitted through watertight bulkheads are to be of equivalent construction to the bulkhead in which they are fitted, permanently attached, capable of being closed watertight from both sides of the bulkhead and are to be tested watertight.

7.16.3 Doors or hatches are not to be fitted in collision bulkheads, except in craft of less than 21 m Rule length, L _R, or where it would be impracticable to arrange access to the forepeak other than through the collision bulkhead. Where fitted, such doors or hatches are to be watertight, as small as practicable and are to open into the forepeak compartment. Consideration will be given to operation from one side only. Doors or hatches in collision bulkheads are to be kept closed at all times while the craft is at sea.

7.16.4 Particular attention is to be given to the design and workmanship of adequate access manholes in tanks.

7.16.5 Where a manhole is fitted in a tank, the exposed edges of all openings cut in sandwich panels are to be suitably sealed. In general, a high density foam core (or equivalent material) is to be used around the perimeter of such openings. Exposed edges in way of cut-outs in sandwich panels are to be overlaminated with a weight of laminate not less than that required for the skin of the sandwich panel exposed to the fluid or as required by Pt 8, Ch 3, 2.5 Minimum skin reinforcement in sandwich laminates 2.5.1, whichever is the greater, see Pt 8, Ch 3, 2.3 Sandwich skin laminate 2.3.1.

7.16.6 Manhole covers are to be attached using bolts/studs spaced at not greater than six diameters. The cover is to be fitted on a suitable seal. Where studs or bolts used to attach the cover plate to the manhole pass through the laminate, they are to be suitably secured, sealed and over-laminated.

7.17.1 Integral/deep tanks are to be tested by air pressure or by a head of water. If tested by water, the head is to be either to 1,8 m above the crown of the tank or to the top of the air or overflow pipe, whichever is the greater. When tested by air, the pressure is not to exceed 0,014 N/mm². The head to which the tank will be subjected in service is to be indicated on the plans submitted.