Section 5 Hatch coamings

5.1.1 The height of coamings above the upper surface of the deck, measured above sheathing if fitted, for hatchways closed by portable covers secured weathertight by tarpaulins and battening devices, is to be not less than:

• 600 mm at Position 1,
• 450 mm at Position 2.

5.1.2 Where hatches in locations above Position 2 are included in the consideration of intact and damage stability or are in critical locations above Position 2, then the height of hatch coamings is to be specially considered.

5.1.3 The height of coamings of hatchways situated in Positions 1 and 2 closed by steel covers fitted with gaskets and clamping devices are to be as specified in Pt 3, Ch 11, 5.1 General 5.1.1, 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. The agreement of the National Authority concerned will also be required.

5.1.4 The height of coamings may be required to be increased on ships of Type `B-100' or Type `B-60' where this is shown to be necessary by the floatability calculations required by the International Convention on Load Lines, 1966.

5.2.1 Vertical cargo hatch coamings 600 mm or more in height are to be stiffened on their upper edges by a horizontal bulb flat or equivalent which is to be not less than 180 mm in width for ships where L is greater than 75 m. Additional support is to be afforded by fitting brackets or stays from the bulb flat to the deck at intervals of not more than 3 m. Each bracket or stay is to be aligned with suitable underdeck stiffeners and is to have a softened nose.

5.2.2 Vertical coamings less than 600 mm in height are to be stiffened at their upper edge by a substantial rolled or fabricated section. Additional support is to be arranged as required by Pt 3, Ch 11, 5.2 Construction 5.2.1.

5.2.3 Cargo hatchways on other decks, in positions not specified in Pt 3, Ch 1, 6.6 Position 1 and Position 2, are to be suitably framed.

5.2.4 The scantlings and arrangements of hatch coamings acting as girders will be specially considered. The coamings are to be arranged with intermediate continuous horizontal stiffeners supported by the bracket stays.

5.2.5 Sloped cargo hatch coamings will be specially considered. In general, the sloped coaming arrangement is to be restricted to the hatch side coamings with vertical coamings at the ends. The sloped coaming is not to have a knuckle and the angle to the vertical is not to exceed 30°. The scantlings are to be in accordance with Pt 3, Ch 11, 5.2 Construction 5.2.1, Pt 3, Ch 11, 5.2 Construction 5.2.2 and Pt 3, Ch 11, 5.3 Strength criteria, except that the end coamings are to be increased by 20 per cent for a distance of 0,15b from the side coamings where b is the width of the hatchway at the deck. Particular care is to be taken where the proposed loadings exceed those given in Pt 3, Ch 11, 2.3 Load model and Pt 3, Ch 3, 5 Design loading, and where the coamings are not in alignment with the topside tank vertical strake in bulk carriers.

5.2.6 A radiused coaming plate at the corner junction of the longitudinal and transverse cargo hatch coamings is acceptable for ships where L ≤ 90 m and the heights of coamings are not in excess of that specified in Pt 3, Ch 11, 5.1 General 5.1.1. Where L > 90 m the corner junctions are to be rectangular and arranged with continuation brackets as required by Pt 3, Ch 11, 5.2 Construction 5.2.8.

5.2.7 The deck plating is to extend inside the coamings and the side coamings are to be extended in the form of tapered brackets. A recommended arrangement is shown in Figure 11.5.1 Coaming continuation bracket - Recommended arrangement. Continuation brackets are also to be arranged athwartships in line with the hatch end coamings and the under deck transverse. In bulk carriers the athwartship brackets, in conjunction with the hatch end beams should be arranged to achieve a satisfactory overlap with the top side tank transverses. In cases where the hatch end beam is formed by the transverse bulkhead top stool the horizontal knuckle of the stool should be arranged well clear of the topside tank knuckle line.

Figure 11.5.1 Coaming continuation bracket - Recommended arrangement

5.2.8 In bulk carriers where the hatch side coaming does not align with the topside tank vertical strake the arrangement and scantlings will be specially considered. In general, suitable underdeck girders and cantilever brackets are to be arranged taking into consideration the hatch cover loading. The underdeck girders are to continue beyond the hatch end for a distance of 2H _c mm. Alternative arrangements incorporating bulkhead top stool structure or cross-deck structure will be considered.

5.2.9 Extension brackets or rails arranged approximately in line with the cargo hatch side coamings and intended for the stowage of steel covers are not to be welded to a deckhouse, masthouse or to each other unless they form part of the longitudinal strength members.

5.2.10 The arrangement and scantlings of continuous hatchway coamings on the strength deck will be specially considered. The material of the coamings is to comply with Table 2.2.1 Material classes and grades and Table 2.2.2 Steel grades in Pt 3, Ch 2 Materials and is to be of the same strength level as the deck plating. Discontinuous coamings of length greater than 0,09L are also to satisfy this requirement.

5.2.11 Where containers are carried on multi-panel hatch covers, the hatch coaming in way of the loaded panel will be required to be reinforced to resist the lateral loads imposed on the coaming due to rolling of the ship. Thrust blocks are to be fitted on the coaming rest bar to prevent the covers from moving. Where one-piece hatch covers are fitted with locating devices, the coamings are to be reinforced in way of the locators.

5.2.12 Cut outs in the top of hatch coamings are to be avoided. Where these are necessary for the securing devices they are to be circular or elliptical in shape. Also any local reinforcements should be given a tapered transition in the longitudinal direction with a taper the rate of which should not exceed 1 in 3. Cut-outs and drain holes are to be avoided in the hatch side coaming continuation brackets. Where these are necessary the size, shape and position will be specially considered.

5.2.13 Material for hatch coamings is to be steel, according to the requirements for ship’s hull. Alternative materials will be subject to special consideration.

5.2.14 Secondary stiffeners of hatch coamings are to be continuous over the breadth and length of hatch coamings.

5.2.15 Longitudinal hatch coamings with a length exceeding 0,1L m are to be provided with tapered brackets or equivalent transitions and a corresponding substructure at both ends. At the end of the brackets they are to be connected to the deck by full penetration welds of minimum 300 mm in length.

5.2.16 Hatch coamings and supporting structures are to be adequately stiffened to accommodate the loading from hatch covers, in longitudinal, transverse and vertical directions. Structures under deck are to be checked against the load transmitted by coaming stays.

5.2.17 On ships carrying cargo on deck, such as timber, coal or coke, coaming stays are to be spaced not more than 1,5 m apart.

5.2.18 Coaming plates are to extend to the lower edge of the deck beams; they or hatch side girders are to be fitted that extend to the lower edge of the deck beams. Extended coaming plates and hatch side girders are to be flanged or fitted with face bars or half-round bars. Figure 11.5.2 Example of hatch side girder and Figure 11.5.3 Example of coaming stays give examples.

Figure 11.5.2 Example of hatch side girder

5.3.1 The strength requirements in this Section are applicable to hatch coamings of stiffened plate construction.

5.3.2 The local net plate thickness of weather deck hatch coamings is not to be less than the larger of the following values:

5.3.3 Secondary stiffeners of coamings must be continuous at the coaming stays. For stiffeners with both ends constrained, the elastic net section modulus Z in cm³ and net shear area A _S in cm², calculated on the basis of net thickness, are not to be less than:

5.3.4 For sniped stiffeners at coaming corners, section modulus and shear area at the fixed support are to be increased by 35 per cent. The gross thickness of the coaming plate at the sniped stiffener end is not to be less than:

5.3.5 Coaming stays are to be designed for the loads transmitted through them, and permissible stresses according to Pt 3, Ch 11, 2.4 Allowable stress and deflection 2.4.1.

5.3.6 At the connection with deck, the net section modulus Z, in cm³, and the gross thickness t_w, in mm, of the coaming stays designed as beams with flange (examples 1 and 2 are shown in Figure 11.5.3 Example of coaming stays) are to be taken not less than:

5.3.7 For other designs of coaming stays, such as those shown in examples 3 and 4 in Figure 11.5.3 Example of coaming stays, the stresses are to be determined through FEM. The calculated stresses are to comply with the permissible stresses according to Pt 3, Ch 11, 2.6 Local plate thickness of hatch covers for wheel loading and helicopter landing.

Figure 11.5.3 Example of coaming stays

5.3.8 Coaming stays are to be supported by appropriate substructures. Face-plates may be included in the calculation only if an appropriate substructure is provided and welding ensures an adequate joint.

5.3.9 Webs of coaming stays are to be connected to the deck by fillet welds on both sides with a throat thickness of a = 0,44t _w.

5.3.10 For coaming stays which transfer friction forces at hatch cover supports, fatigue strength is to be considered, see Pt 3, Ch 11, 4.2 Steel covers − Clamped and gasketed 4.2.5 to Pt 3, Ch 11, 4.2 Steel covers − Clamped and gasketed 4.2.8.

5.3.11 Hatch coamings which are part of the longitudinal hull structure are to be designed according to the requirements for longitudinal strength in Pt 3, Ch 4 Longitudinal Strength.

5.3.12 For structural members welded to coamings and for cut-outs in the top of coamings, sufficient fatigue strength is to be verified.

5.4.1 Rest bars are to provide at least 65 mm bearing surface and are to be aligned if required to suit the slope of the hatches.

5.5.1 For weather deck hatch side coamings forming part of a hatch side girder subjected to loading exceeding that defined in Pt 3, Ch 11, 2.3 Load model, see Pt 4, Ch 1, 4 Deck structure.