Section 2 Hatches and miscellaneous openings on the weather deck

2.1.1 The hatch covers on the weather decks of all ships are to be steel plated, stiffened by webs or stiffeners, hinged and secured by clamping devices. Weathertightness to be achieved by means of gaskets. The means of securing are to be such that weathertightness can be maintained in any sea condition. Where toggles are fitted, their diameter and spacing are to be in accordance with ISO standards or equivalent.

2.1.2 The scantlings of covers are not to be less than the rule thickness for the deck at that point. Where other materials are used, equivalent scantlings are to be provided. The scantlings apply basically to rectangular covers, with the stiffening members arranged primarily in one direction and carrying a uniformly distributed load. The covers are assumed to be simply supported. Where covers are stiffened by a grillage formation, and also where point loads are applied to any type of cover, the scantlings are to be determined from direct calculations.

2.1.3 In the case of flush hatch covers or of covers on coamings of lesser height than required by Vol 1, Pt 3, Ch 4, 2.3 Manholes and flush escape hatches 2.3.1, their scantlings, the securing and sealing arrangements and the drainage of gutterways will be specially considered.

2.1.4 Where hatchways are trunked through one or more lower decks, and hatchway beams and covers are dispensed with at the intermediate decks, the hatchway beams, coamings and covers immediately below the trunk are to be adequately strengthened. Plans are to be submitted for approval.

2.1.5 Small hatches, including escape hatches, are to be situated clear of RADHAZ areas and RAS stores receiving areas and storing routes. Small hatches and their securing devices are to be easily operable by one person in the expected operating conditions; this is typically achieved if the maximum operating force does not exceed 150N. Where necessary, counterbalance weights, springs or other equivalent mechanisms are to be provided to assist the user in opening and closing the hatch. Any mechanism fitted is to be designed so as not to present a hazard to persons using the hatch. Failure of the mechanism is not to prevent the operation of the hatch.

2.1.6 Where practicable access hatches to below spaces are to be arranged to allow for the passage of personnel wearing breathing apparatus as well as the transfer of injured personnel. For this purpose the opening is to be a minimum of 600mm x 600mm. Hand holds and foot holds are to be located both within the space being accessed and externally in the vicinity of hatch so as to enable ease of access.

2.1.7 Where portable plates are required in decks for unshipping machinery, or for other similar reasons, they may be accepted provided they are of equivalent strength to the unpierced deck or the surrounding structure is suitably compensated. Portable plates are to be secured by gaskets and closely spaced bolts at a pitch not exceeding five diameters or equivalent naval standard.

2.2.1 The height of coamings above the upper surface of the weather deck, measured above sheathing if fitted, is to be not less than 300 mm. For exposed decks immediately above the design draught, e.g. quarter decks and well decks, coaming heights are to be no less than 600 mm. Coaming of a height no less than 450 mm may be provided if the hatch cover is kept closed and a small access hatch is provided in the hatch cover.

2.2.2 The height of coamings of hatchways closed by steel covers fitted with gaskets and clamping devices are to be as specified in Vol 1, Pt 3, Ch 4, 2.2 Hatch coamings 2.2.1, but may be reduced, or the coamings may be omitted entirely, if the safety of the ship is not thereby impaired in any sea condition. Special attention will be given in such cases to the scantlings of the covers, to their gasketing and securing arrangements and to the drainage of recesses in the deck.

2.2.3 The height of coamings may be required to be increased on ships where this is shown to be necessary by the stability and watertight subdivision calculations required by Vol 1, Pt 3, Ch 2, 1.3 Watertight and weathertight integrity.

2.2.4 Vertical coamings are to have a thickness, t, in mm not less than the greater of the following:

1. 

2. Rule thickness of the deck in the position fitted

2.2.5 Vertical coamings are to be stiffened at their upper edge by a substantial rolled or fabricated section. Additional support is to be arranged as necessary.

2.3.1 Manholes are to be closed by substantial covers capable of being made watertight. The covers are to be permanently attached.

2.3.2 Flush escape hatches are to be closed by substantial weathertight covers capable of being opened and closed from either side unless specified otherwise for hatches that provide access to high security areas such as magazines or to prevent access from open decks. The covers are to be permanently attached.

2.4.1 The requirements of this Section are to be complied with where it is necessary to maintain the weathertight envelope.

2.4.2  Access hatches within a superstructure or deckhouse need not be provided with means for closing if all openings in the surrounding bulkheads have weathertight closing appliances.

2.4.3 Consideration should be given to positioning weathertight or gastight hatches on lower decks in accordance with a specified standard for CBRN purposes.

2.5.1 Openings on the tops and sides of enclosed structures on the weather deck up to a height of 2,5 m are to be weathertight. In the forward 0,25L _R the height should be taken to 5 m. The height of openings may be required to be increased where this is shown necessary by the stability and watertight subdivision calculation required by Vol 1, Pt 1, Ch 2, 1.1 Framework of Classification. The weather deck as defined in Vol 1, Pt 3, Ch 1, 5.4 Decks 5.4.2 may be stepped or recessed for the purpose of this Chapter. Special consideration will be given to the position of the weather deck of NS1 ship types.

2.6.1 Where blow out plates are required they are to be secured by sealing arrangements adequate to meet the weathertightness and operational requirements. They are to be of an equivalent strength to the deck in which they are fitted.

2.6.2 Blow out plates are to be permanently attached.