Common Structural Rules - Common Structural Rules for Bulk Carriers and Oil Tankers, January 2019 - Part 2 Ship Types - Chapter 1 Bulk Carriers - Section 5 Cargo Hatch Covers - 7 Weathertightness, Closing Arrangement, Securing Devices and Stoppers
7 Weathertightness, Closing Arrangement, Securing Devices and Stoppers
7.1 Weathertightness
7.1.1 Where the hatchway is exposed, the weathertightness is to be ensured by gaskets and clamping devices sufficient in number and quality.
7.1.2 In general, a minimum of two securing devices or equivalent is to be provided on each side of the hatch cover.
7.2 Gaskets
7.2.1 The weight of hatch covers and any cargo stowed thereon, together with inertia forces generated by ship motions, are to be transmitted to the ship’s structure.
7.2.2 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 to be made of a corrosion-resistant material.
7.2.3 The gasket and the securing arrangements are to maintain their efficiency when subjected to large relative movements between the hatch cover and the ship’s structure or between hatch cover elements.
If necessary, suitable devices are to be fitted to limit such movements.
7.2.4 The gasket material is to be of a quality suitable for all environmental conditions likely to be encountered by the ship, and is to be compatible with the cargoes transported.
The material and form of gasket selected are to be considered in conjunction with the type of hatch cover, the securing arrangement and the expected relative movement between the hatch cover and the ship’s structure.
The gasket is to be effectively secured to the hatch cover.
7.2.5 Coamings and steel parts of hatch covers in contact with gaskets are to have no sharp edges.
7.2.6 Metallic contact is required to ensure earthing connection between the hatch cover and the hull structures.
7.3 Closing arrangement, securing devices and stoppers
7.3.1 General
Panel hatch covers are to be secured by appropriate devices (bolts, wedges or similar) suitably spaced along the coamings and between cover elements.
Hatch covers provided with special sealing devices, insulated hatch covers, flush hatch covers and those having coamings of a reduced height according to [2.1.2] are to be considered by the Society on a case-by-case basis.
7.3.2 Arrangements
The securing and stopping devices are to be arranged so as to ensure sufficient compression on gaskets between hatch covers and coamings and between adjacent hatch covers.
Arrangement and spacing are to be determined with due attention to the effectiveness for weathertightness, depending on the type and the size of the hatch cover, as well as on the stiffness of the hatch cover edges between the securing devices.
At cross-joints of multi-panel covers, (male/female) vertical guides are to be fitted to prevent excessive relative vertical deflections between loaded/unloaded panels.
The location of stoppers is to be compatible with the relative movements between hatch covers and the ship’s structure in order to prevent damage to them. The number of stoppers is to be as small as possible.
7.3.3 Spacing
The spacing of the securing arrangements is not to be greater than 6 m.
7.3.4 Construction
Securing arrangements with reduced scantlings may be accepted provided it can be demonstrated that the possibility of water reaching the deck is negligible.
Securing devices are to be of reliable construction and securely attached to the hatchway coamings, decks or hatch covers.
Individual securing devices on each hatch cover are to have approximately the same stiffness characteristics.
7.3.5 Area of securing devices
The gross cross area of each securing device is not to be less than the value obtained, in cm2, from the following formula:
where:
SS : Spacing, in m, of securing devices.
- α = 0.75 for ReH > 235 N/mm2.
- α = 1.0 for ReH ≤ 235 N/mm2.
In the above calculations, ReH may not be taken greater than 0.7 Rm.
Between hatch cover and coaming and at cross-joints, a packing line pressure sufficient to obtain weathertightness is to be maintained by securing devices. For packing line pressures exceeding 5 N/mm, the net cross area A is to be increased in direct proportion. The packing line pressure is to be specified.
In the case of securing arrangements which are particularly stressed due to the unusual width of the hatchway, the net cross area A of the above securing arrangements is to be determined through direct calculations.
7.3.6 Inertia of edges elements
The hatch cover edge stiffness is to be sufficient to maintain adequate sealing pressure between securing devices.
The moment of inertia of edge elements is not to be less than the value obtained, in cm4, from the following formula:
where:
PL : Packing line pressure, in N/mm, to be taken not less than 5.
SS : Spacing, in m, of securing devices.
7.3.7 Diameter of rods or bolts
Rods or bolts are to have a gross diameter not less than 19 mm for hatchways exceeding 5 m2 in area.
7.3.8 Stoppers
Hatch covers are to be effectively secured, by means of stoppers, against the transverse forces arising from a pressure of 175 kN/m2.
With the exclusion of No. 1 hatch cover, hatch covers are to be effectively secured, by means of stoppers, against the longitudinal forces acting on the forward end arising from a pressure of 175 kN/m2.
No. 1 hatch cover is to be effectively secured, by means of stoppers, against the longitudinal forces acting on the forward end arising from a pressure of 230 kN/m2. This pressure may be reduced to 175 kN/m2 if a forecastle is fitted in accordance with Ch 1, Sec 1, [1].
The equivalent stress in stoppers, their supporting structures and calculated in the throat of the stopper welds is to be equal to or less than the allowable value, equal to 0.8 ReH.
7.4 Cleats
7.4.1 Where rod cleats are fitted, resilient washers or cushions are to be incorporated.
7.4.2 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.
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