6 Hatch Coamings

6.1 Stiffening

6.1.1 The stiffeners of the hatch coamings are to be continuous over the breadth and length of the hatch coamings.

6.1.2 Coamings are to be stiffened on their upper edges with a stiffener suitably shaped to fit the hatch cover closing appliances.

6.1.3 Where the height of the coaming exceeds 900 mm, additional strengthening may be required. However, reductions may be granted for transverse coamings in protected areas.

6.1.4 When two hatches are close to each other, under deck stiffeners are to be fitted to connect the longitudinal coamings in order to maintaining the continuity of their strength.

Similar stiffening is to be provided over 2 frame spacings at ends of hatches exceeding 9 frame spacings in length.

In some cases, the Society may require the continuity of coamings to be maintained above the deck.

6.1.5 Where watertight metallic hatch covers are fitted, other arrangements of equivalent strength may be adopted.

6.2 Load model

6.2.1 The wave lateral pressure, P_C in kN/m², to be considered as acting on the hatch coamings is defined in [6.2.2] and [6.2.3].

6.2.2 The wave lateral pressure, P_C in kN/m², on the No. 1 forward transverse hatch coaming is to be taken equal to:

• P_C = 220, when a forecastle is fitted in accordance with Ch 1, Sec 1, [1].
• P_C = 290, in the other cases.

6.2.3 The wave lateral pressure, PC in kN/ m², on the hatch coamings other than the No. 1 forward transverse hatch coaming is to be taken equal to:

P_C = 220

6.2.4 For cargo holds intended for the carriage of ballast water, the liquid internal pressures applied on hatch coaming is also to be determined according to Pt 1, Ch 4, Sec 6.

6.3 Scantlings

6.3.1 Plating

The net thickness, in mm, of the hatch coaming plate is not to be taken less than the greater value given by the following formulae:

t = 9.5

6.3.2 Stiffeners

The net section modulus, Z, in cm³, of longitudinal or transverse stiffeners fitted on hatch coamings is not to be taken less than:

where:

6.3.3 Coaming stays

At the connection with deck, the net section modulus Z, in cm³, and the net thickness t_w, in mm, of the coaming stays designed as beams with flange connected to the deck or sniped and fitted with a bracket (examples shown in Figure 3 and Figure 4) are to be taken not less than:

where:

H_C : Stay height, in m.

s_C : Stay spacing, in mm.

h : Stay depth, in mm, at the connection with deck.

Figure 3 : Coaming stay (example 1)

Figure 4 : Coaming stay (example 2)

For calculating of offered section modulus of coaming stays, the face plate area may be taken into account only when it is welded with full penetration welds to the deck plating and provided with adequate under deck structure supporting the coaming stay in the deck structure.

For other designs of coaming stays, such as those shown in Figure 5 and Figure 6, the stress levels determined through a grillage analysis or finite element analysis, as the case may be, apply and are to be checked at the highest stressed locations. The stress levels are to comply with the following formulae:

σ ≤ 0.95 R_eH

τ ≤ 0.5 R_eH

Figure 5 : Coaming stay (example 3)

Figure 6 : Coaming stay (example 4)

6.3.4 Local details

The design of local details is to comply with the requirements in this section ensuring adequate structural continuity from the hatch covers into the supporting deck structure.

Hatch coamings and supporting structures are to be adequately stiffened to accommodate the loading from hatch covers, in longitudinal, transverse and vertical directions.

The normal stress σ and the shear stress τ, in N/mm², induced in the under deck structures by the loads transmitted by stays are to comply with the following formulae:

σ ≤ 0.95 R_eH

τ ≤ 0.5 R_eH

Unless otherwise stated, weld connections and materials are to be dimensioned and selected in accordance with the requirements of the Society.

Double continuous fillet welding is to be adopted for the connections of stay webs with deck plating and the weld leg length is not to be less than 0.62 t_w, where t_w is the gross thickness of the stay web.

Toes of stay webs are to be connected to the deck plating with partial penetration double bevel welds extending over a distance not less than 15% of the stay width.