Section 4 Hatch cover securing arrangements and tarpaulins

4.1.1 For access hatchways to cargo oil tanks and adjacent spaces, see Pt 3, Ch 11, 7 Tanker access arrangements and closing appliances.

4.2.1 These requirements, unless stated otherwise, apply to steel hatch covers in Positions 1 and 2 fitted with gaskets and securing devices and situated above dry cargo holds.

4.2.2 Where steel hatch covers are fitted to hatch openings on weather decks, the arrangements are to be such that weathertightness can be maintained. A sufficient number of securing devices is to be provided at each side of the hatch cover, considering the requirements of Pt 3, Ch 11, 2.9 Net scantling of primary supporting members 2.9.4 to Pt 3, Ch 11, 2.9 Net scantling of primary supporting members 2.9.6. This applies also to hatch covers consisting of several parts.

4.2.3 The weight of the covers and weather loading may be transmitted to the ship's structure by means of continuous steel to steel contact of the cover skirt plate with the ship's structure in association with a maximum bearing pressure of 200 kgf/cm². Alternatively the weight may be transmitted by means of defined bearing pads. For covers loaded by containers or other cargo, the total load together with inertial forces generated by the ship's motion, are to be transmitted by means of defined bearing pads only.

4.2.4 For the design of the securing devices against shifting, the horizontal mass forces F _h = m · a are to be calculated with the following accelerations:

The accelerations in longitudinal direction and in transverse direction do not need to be considered as acting simultaneously.

4.2.5 For the transmission of the support forces resulting from the load cases specified in Pt 3, Ch 11, 2.3 Load model and of the horizontal mass forces specified in Pt 3, Ch 11, 4.2 Steel covers − Clamped and gasketed 4.2.4, hatch cover supports are to be provided, which are to be designed such that the nominal surface pressures do not, in general, exceed the following values:

For metallic supporting surfaces not subjected to relative displacements, the nominal surface pressure applies:

When the maker of vertical hatch cover support material can provide proof that the material is sufficient for the increased surface pressure, not only statically but under dynamic conditions including relative motion for an adequate number of cycles, permissible nominal surface pressure may be specially considered. In this case, realistic long-term distribution of spectra for vertical loads and relative horizontal motion is to be required to be considered.

The supports are to be designed such that the permissible stresses according to Pt 3, Ch 11, 2.4 Allowable stress and deflection 2.4.1 are not exceeded.

4.2.6 Drawings of hatch cover supports which specify the permitted maximum pressure, given by the material manufacturer, must be submitted.

4.2.7 Where large relative displacements of the supporting surfaces of hatch cover supports are to be expected, the use of material having low wear and frictional properties is recommended.

4.2.8 The substructures of the hatch cover supports must be of such a design that a uniform pressure distribution is achieved. Irrespective of the arrangement of stoppers, the supports must be able to transmit the following force P _h in the longitudinal and transverse direction:

where

For non-metallic, low-friction support materials on steel, the friction coefficient may be reduced, but is not to be less than 0,35. The substructures are to be designed such that the permissible stresses according to Pt 3, Ch 11, 2.4 Allowable stress and deflection 2.4.1 are not exceeded.

4.2.9 For substructures and adjacent structures of supports subjected to horizontal forces P _h, as defined in Pt 3, Ch 11, 4.2 Steel covers − Clamped and gasketed 4.2.8, the fatigue strength is to be considered.

4.2.10 Hatch covers are to be sufficiently secured against horizontal shifting. Stoppers are to be provided for hatch covers on which cargo is carried. The greater of the loads resulting from Pt 3, Ch 11, 2.3 Load model 2.3.3 and Pt 3, Ch 11, 4.2 Steel covers − Clamped and gasketed 4.2.4 is to be applied for the dimensioning of the stoppers and their substructures. The permissible stress in stoppers and their substructures in the cover and in the coamings is to be determined according to Pt 3, Ch 11, 2.4 Allowable stress and deflection 2.4.1. In addition, the provisions in Pt 3, Ch 11, 4.2 Steel covers − Clamped and gasketed 4.2.5 are to be observed.

4.2.11 The sealing is to be obtained by a continuous gasket of relatively soft elastic material compressed to achieve the necessary weathertightness. Similar sealing is to be arranged between cross-joint elements. Where fitted, compression flat bars or angles are to be well rounded where in contact with the gasket and are to be made of a corrosion-restraint material or suitably protected against corrosion.

4.2.12 Special consideration is to be given to the gasket and securing arrangements in ships with large relative movements between cover and ship structure or between cover elements. The relative horizontal and vertical deflections are to be calculated and submitted with the hatch cover plans. Where applicable, deflections due to thermal effects and internal pressure loads are also to be included.

4.2.13 The suitability of the gasket material and the securing adhesive is the responsibility of the Builder and Owner. When selecting such material, consideration is to be given to its suitability for the environmental conditions likely to be experienced by the ship and its compatibility with the cargo carried. The material and form of gasket selected is to be considered in conjunction with the type of cover, the securing arrangement and the expected relative movement between cover and ship structure. The gasket is to be effectively secured to the cover.

4.2.14 Drainage is to be arranged inside the line of gasket by means of a gutter bar or vertical extension of the hatch side and end coaming; drain openings are to be provided at appropriate positions on the drain channels. This requirement need not be complied with for special ships carrying container cargoes when the requirements of Pt 4, Ch 8, 11 Hatch coversare satisfied.

4.2.15 Where the arrangement includes continuous steel to steel contact between hatch cover and coaming or between hatch cover and ship structure or at cross-joints, drainage on both sides of the gasket is to be provided.

4.2.16 Drain openings are to be arranged at the ends of drain channels and are to be provided with non-return valves for preventing ingress of water from outside.

The following requirements are to be complied with:

1. If manufactured from steel, the minimum drain pipe wall thickness is to be not less than 4,5 mm.

2. If not manufactured from steel, details of the drain, including the material specification, method of manufacture and details of any tests carried out, are to be submitted for consideration.

3. The drains are to be securely attached to the hatch coaming and adequately protected if in an exposed position.

4. When the drain is fitted to a hold also designed to carry liquids, a shut-off valve is to be incorporated into the assembly.

5. Drain openings in hatch coamings are to be arranged with sufficient distance to areas of stress concentration (e.g. hatch corners, transitions to crane posts).

4.2.17 Panel hatch covers are to be secured by appropriate devices (bolts, wedges or similar) suitably spaced alongside the coamings. The securing devices are not to have a vertical clearance but are to be pre-tensioned when the cover is in the closed position. The devices are also to be arranged in close proximity horizontally to the gasket. Arrangement and spacing are to be determined with due attention to the effectiveness for weathertightness, depending upon the type and the size of the hatch cover, as well as on the stiffness of the cover edges between the securing devices. A minimum of two securing devices for each side of a panel are to be fitted. The securing devices should be arranged as close to the panel corners as is practicable.

4.2.18 Between cover and coaming and at cross-joints, a gasket pressure sufficient to obtain weathertightness is to be maintained by the securing devices. This pressure is to be specified. Securing devices of a design other than rod or bolts will be specially considered, see Pt 3, Ch 11, 4.2 Steel covers − Clamped and gasketed 4.2.26.

4.2.19 The net sectional area of each securing device is to be not less than:

where

f	=
S 1	=	spacing between securing devices, in metres, not to exceed 6 m and not to be taken less than 2 m
W 1	=	the gasket loading per unit length, in N/cm, but not less than 50 N/cm
σc	=	specified minimum upper yield stress in N/mm2 of the steel used for cleats or securing devices, to be taken not greater than 70 per cent of the ultimate tensile strength
e	=	0,75 for σc ≥ 235
	=	1,0 for σc< 235.

4.2.20 Rods or bolts are to have a gross diameter not less than 19 mm for hatchways exceeding 5 m² in area.

4.2.21 In order to ensure compression between gasket and compression bar along the full length, the cover edge stiffness is to be examined. The inertia of the cover edge is to be not less than:

E

=

0,6W 1 S 1 4 cm4

where W ₁ and S ₁ are as defined in Pt 3, Ch 11, 4.2 Steel covers − Clamped and gasketed 4.2.12.

4.2.22 Securing devices are to be constructed of reliable design and securely attached to the hatchway coamings, decks or covers. Individual securing devices on each cover are to have approximately the same stiffness characteristics.

4.2.23 Where rod cleats are fitted, resilient washers or cushions are to be incorporated.

4.2.24 Where hydraulic cleating is adopted, a positive means is to be provided to ensure that it remains mechanically locked in the closed position in the event of failure of the hydraulic system.

4.2.25 The cross-joints of multi-panel covers are to be arranged with wedges, or locators (male and female) to retain the hatch covers in the correct sealing position, the number and spacing is to be arranged to suit the size and type of cover, gasket arrangements and stiffness of cover edges at cross-joints. Means are also to be provided to prevent excessive relative vertical deflections between loaded and unloaded panels. The arrangement of the gasket retaining angle and the compression bar at the cross-joints is to be such that the gasket compression is maintained between loaded and unloaded panels.

4.2.26 In addition to the requirements given above, all hatch covers, especially those carrying deck cargo are to be effectively secured against horizontal shifting due to the horizontal forces arising from the ship motions.

4.2.27 To prevent damage to hatch covers and ship structure, the location of stoppers is to be compatible with the relative movements between hatch covers and ship structure. The number should be as small as practically possible.

4.2.28 Towards the ends of the ship, vertical acceleration forces may exceed gravity forces. The resulting lifting forces must therefore be also considered when dimensioning the securing devices. Also lifting forces from cargo secured on the hatch cover during rolling are to be taken into account.

4.2.29 Hatch coamings and supporting structure are to be adequately stiffened to accommodate the loading from hatch covers and cargo carried thereon.

4.2.30 Upon completion of installation of hatch covers, a hose test with a pressure of water as specified in Table 1.9.1 Testing requirements in Chapter 1 is to be carried out. Alternative methods of tightness testing will be considered. This does not apply to covers with reduced securing arrangements as specified in Pt 4, Ch 8, 11 Hatch covers.

4.2.31 All hatch covers are to be tested to prove satisfactory operation.

4.2.32 It is recommended that ships with steel hatch covers are supplied with an operation and maintenance manual including:

1. opening and closing instructions;

2. maintenance requirements and specifications for packings, securing devices and operating items;

3. cleaning instructions for the drainage system;

4. corrosion prevention instructions;

5. list of spare parts.

4.2.33 The spacing and size of securing devices in hatch covers for holds which may be flooded and used for ballast tanks and holds in OBO, ore or oil and similar types of ship are to correspond to the reaction forces at the cover edges found by calculation. The loading is to be as required by Pt 4, Ch 7, 12.4 Load model 12.4.1.(c).

The permissible stress in the securing devices is not to exceed the following:

σ e	=	0,9 × 235 f N/mm2
	=	where
f	=	material factor as defined in Pt 3, Ch 11, 4.2 Steel covers − Clamped and gasketed 4.2.19
σ	=	bending stress in N/mm2
σe	=	equivalent stress, in N/mm2
	=
τ	=	shear stress in N/mm2

4.2.34 On tank hatch covers in 'tween decks the maximum spacing of cleats is to be 600 mm, but cleats are to be arranged as close to the corners as practicable.

4.2.35 Steel hatch covers with special sealing arrangements, insulated covers, flush hatch covers, and covers having coamings less than required by Pt 3, Ch 11, 5.1 General, will be specially considered.

4.2.36 The material and weld specifications of stoppers and securing devices are to be shown in the drawings of the hatch covers.

4.2.37 Securing devices of special design in which significant bending or shear stresses occur may be designed as anti-lifting devices according to Pt 4, Ch 8, 11.2 Direct calculations 11.2.6. The packing line pressure, as defined in Pt 3, Ch 11, 4.2 Steel covers − Clamped and gasketed 4.2.12, multiplied by the spacing between securing devices, as defined in Pt 3, Ch 11, 4.2 Steel covers − Clamped and gasketed 4.2.12, is to be applied as design load.

4.3.1 At least two layers of tarpaulin in good condition are to be provided for each hatchway in Positions 1 and 2.

4.3.2 Tarpaulins are to be free from jute, waterproof and of ample strength. The minimum mass of the material before treatment is to be 0,65 kg/m² if the material is to be tarred, 0,60 kg/m² if to be chemically dressed, or 0,55 kg/m² if to be dressed with black oil. A certificate to this effect is to be supplied by the makers of the tarpaulins. Special consideration will be given to the use of synthetic materials for tarpaulins.

4.3.3 Cleats are to be of an approved pattern, at least 65 mm wide, with edges so rounded as to minimise damage to the wedges, and are to be spaced not more than 600 mm from centre to centre: the first and last cleats along each side or end are to be not more than 150 mm from the hatch corners. Cleats should be so set as to fit the taper of the wedges.

4.3.4 Battens and wedges shall be efficient and in good condition. Wedges are to be of tough wood, generally not more than 200 mm in length and 50 mm in width. They should have a taper of not more than 1 in 6 and should not be less than 13 mm at the point.

4.3.5 For all hatchways in Positions 1 and 2, steel bars or other equivalent means are to be provided in order to secure each section of hatch covers efficiently and independently after the tarpaulins are battened down. Hatch covers of more than 1,5 m in length are to be secured by at least two such securing appliances. Where hatchway covers extend over intermediate supports, steel bars or their equivalent are to be fitted at each end of each section of covers. At all other hatchways in exposed positions on weather decks, ring bolts or other fittings suitable for lashings are to be provided.

4.4.1 Packing material is to be suitable for all expected service conditions of the ship and is to be compatible with the cargoes to be transported. The packing material is to be selected with regard to dimensions and elasticity in such a way that expected deformations can be carried. Forces are to be carried by the steel structure only.

4.4.2 Packing material is to be compressed so as to give the necessary tightness effect for all expected operating conditions. Special consideration will be given to the packing arrangement in ships with large relative movements between hatch covers and coamings or between hatch cover sections.