Section 7 Bulkheads and deep tanks

7.1.1 The requirements of this Section apply to a vertical system of stiffening on bulkheads. They may also be applied to a horizontal system of stiffening provided that equivalent support and alignment are provided.

7.1.2 The number and disposition of transverse watertight bulkheads are to be in accordance with Pt 3, Ch 2, 4 Bulkhead arrangements.

7.1.3 Bulkheads, or part bulkheads, forming the boundary of tanks are to comply with the requirements of Pt 7, Ch 3, 7.5 Deep tank stiffening and Pt 7, Ch 3, 7.6 Double bottom tanks.

7.1.4 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.

7.1.5 A centreline bulkhead is, generally, to be fitted in deep tanks which extend from side to side. The bulkhead may be intact or perforated as desired. If intact, the scantlings are to comply with the requirements of Pt 7, Ch 3, 7.5 Deep tank stiffening and Pt 7, Ch 3, 7.6 Double bottom tanks for tank boundary bulkheads. If perforated, they are to comply with the requirements of Pt 7, Ch 3, 7.13 Wash plates for washplates.

7.1.6 The minimum requirements in Pt 7, Ch 3, 2 Minimum thickness requirements are to be complied with.

7.2.1 The thickness of the watertight bulkhead plating is to be determined from the general plating equation given in Pt 7, Ch 3, 1.16 Plating general using the design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate.

7.3.1 The Rule requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 7, Ch 3, 1.17 Stiffening general, using the design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients using the appropriate load model.

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

7.4.1 The thickness of deep tank plating is to be determined from the general plating equation given in Pt 7, Ch 3, 1.16 Plating general using the design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate.

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.

7.5.1 Deep tank bulkhead stiffeners are to be bracketed at both ends.

7.5.2 Stiffening on a perforated centreline bulkhead in a tank that extends from side to side may be 50 per cent of that required for boundary bulkheads, using a head measured to the crown of the tank.

7.5.3 The Rule requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 7, Ch 3, 1.17 Stiffening general, using the design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients for load model (b).

7.6.1 The scantlings of double bottom tanks are to comply with the requirements for deep tanks given in Pt 7, Ch 3, 7.4 Deep tank plating and Pt 7, Ch 3, 7.5 Deep tank stiffening.

7.6.2 Where the crown of a double bottom tank forms a vehicle, passenger or other deck, the requirements of Pt 7, Ch 3, 8 Deck structures are to be complied with.

7.7.1 The scantlings of collision bulkheads are to comply with the requirements of Pt 7, Ch 3, 7.2 Watertight bulkhead plating and Pt 7, Ch 3, 7.3 Watertight bulkhead stiffening except that the thickness of plating and modulus of stiffeners are not to be less than 12 and 25 per cent greater respectively, than required by Pt 7, Ch 3, 7.2 Watertight bulkhead plating and Pt 7, Ch 3, 7.3 Watertight bulkhead stiffening. If the collision bulkhead forms the boundary of a deep tank or cofferdam then the requirements of Pt 7, Ch 3, 7.4 Deep tank plating and Pt 7, Ch 3, 7.4 Deep tank plating are also to be complied with.

7.8.1 Where gastight bulkheads are fitted, in accordance with Pt 3, Ch 2, 4 Bulkhead arrangements the scantling requirements for watertight bulkheads are to be complied with.

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

7.9.1 Where a bulkhead is structural but non-watertight the scantlings are in general to be as 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 classification.

7.10.1 Bulkheads that are required to act as pillars in way of underdeck girders and other structures subject to heavy loads are to comply with the requirements of Pt 7, Ch 3, 10 Pillars and pillar bulkheads.

7.11.1 The plating thickness and section modulus for symmetrical corrugated bulkheads are to be in accordance with watertight bulkheads or deep tank bulkheads as appropriate. The spacing, s, is to be taken as s _c, as defined in Figure 2.3.1 Corrugation .

7.11.2 In addition, the section geometric properties of Pt 7, Ch 3, 1.18 Geometric properties and proportions of stiffener sections are to be complied with.

7.11.3 The actual section modulus may be derived in accordance with Pt 3, Ch 2, 3.2 Geometric properties of sections.

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

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

7.13.1 Tanks are to be subdivided as necessary by internal baffles or wash plates. Baffles or wash plates which support hull framing are to have scantlings equivalent to web frames in the same position.

7.13.2 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.

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

7.13.4 The general stiffener requirements are to be in accordance with Pt 7, Ch 3, 7.5 Deep tank stiffening. However, the section modulus may be 50 per cent of that required by Pt 7, Ch 3, 7.5 Deep tank stiffening.

7.14.1 A cofferdam is to be fitted between freshwater and fuel oil or sanitary tanks.The scantlings of cofferdams are to comply with the requirements of deep tank bulkheads or non-watertight bulkheads as appropriate.

7.15.1 Integral freshwater and fuel oil tanks need not in general be coated provided they are constructed from suitable marine grade aluminium alloys in accordance with Ch 8 Aluminium Alloys of the Rules for Materials. Where tanks are to be coated, then all surfaces are to be cleaned and dried after testing and then treated with a suitable coating in accordance with the coating manufacturer's recommendations. See Pt 7, Ch 2, 2.6 Paints and coatings.

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

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

7.18.1 Compartments within the craft are to be accessible in order to facilitate proper maintenance and future structural surveys. Linings on craft sides, deckheads 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.

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

7.18.3 Doors and hatches are not to be fitted in collision bulkheads, except in craft of less than 21 metres Rule length or where it would be impracticable to arrange access to the forepeak other than through the collision bulkhead. Where fitted, the doors and hatches are to be watertight, as small as practicable and open into the forepaw compartment. Doors in collision bulkheads are to be kept closed at all times while the craft is at sea, see Pt 3, Ch 2, 4.3 Collision bulkhead 4.3.4.

7.18.4 Particular attention is to be given to the design and workmanship of the tanks, and adequate access manholes are to be fitted, see Pt 3, Ch 1, 7 Inspection, workmanship and testing procedures.

7.19.1 Deep tanks are to be tested on completion, with a head of water to the top of the overflow, or 1,8 m above the crown of the tank, whichever is the greater. The pressure to which the tanks will be subjected in service is to be indicated on the plans submitted.