Section 6 Cargo hatch cover securing arrangements

6.1 Materials and welding

6.1.1 Where stoppers or securing devices are fitted to comply with this section, they are to be manufactured of materials, including welding electrodes, in accordance with Rules for the Manufacture, Testing and Certification of Materials, January 2016 of the Rules for Ships.

6.2 Securing devices

6.2.1 Panel hatch covers are to be secured by appropriate devices (bolts, wedges or similar) suitably spaced along the coamings and between cover elements. Arrangement and spacing are to be determined with due attention to the effectiveness for weather-tightness, 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.

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

Where

a	=	spacing between securing devices, not to be taken less than 2 m
f	=	(σ_Y/235)^e
σ_Y	=	specified minimum upper yield stress in N/mm² of the steel used for fabrication, not to be taken greater than 70 per cent of the ultimate tensile strength
e	=	0,75 for σ_Y > 235
	=	1,0 for σ_Y ≤ 235

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

6.2.3 Between cover and coaming and at cross-joints, a packing line pressure sufficient to obtain weather tightness is to be maintained by the securing devices. For packing line pressures exceeding 5 N/mm, the cross section area is to be increased in direct proportion. The packing line pressure is to be specified.

6.2.4 The cover edge stiffness is to be sufficient to maintain adequate sealing pressure between securing devices. The moment of inertia, I, of edge elements is not to be less than:

Where

p	=	packing line pressure in N/mm, minimum 5 N/mm
a	=	spacing in m of securing devices.

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

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

6.2.7 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.

6.3 Stoppers

6.3.1 Nos. 1 and 2 hatch covers are to be effectively secured, by means of stoppers, against the transverse forces arising from a pressure of 175 kN/m².

6.3.2 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.

6.3.3 No. 2 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.

6.3.4 The equivalent stress in stoppers and their supporting structures, and calculated in the throat of the stopper welds, is not to exceed the allowable value of 0,8σ_Y.