Section 4 Deck plating and continuous longitudinal hatch side coamings

4.1.1 The requirements of this Section cover the topside structure which includes the following structural parts of the ship:

• deck plating and continuous longitudinal hatch coamings.

4.1.2 For ships over 65 m in length, the thickness of the deck and coaming plating may require to be increased to obtain the midship section modulus required in Pt 3, Ch 4 Longitudinal Strength.

4.2.1 The thickness of the deck plating is to comply with Table 1.4.1 Topside structure (general), and is generally to be maintained one frame space fore and aft of the hatch opening. The plating thickness may however be reduced beyond 0,5L amidships in accordance with the requirements for taper given in Pt 3, Ch 3, 2.5 Principles for taper As an alternative, direct calculations may also be used to prove that the allowable stresses given in Section 13 will not be exceeded. The thickness at the end of the hatch opening should however be not less than 80 per cent of the thickness amidships nor less than the minimum thickness required by Table 1.4.1 Topside structure (general).

4.2.2 Openings in the deck should be kept to a minimum and are to be arranged clear of the hatch corners; compensation for these openings will generally be required.

Table 1.4.1 Topside structure (general)

Item and parameter		Requirements for all ships
(1)	Deck thickness	The greater of:
(2)	Hatch coaming	The greater of:
	minimum thickness
(3)	Upper hatch coaming stiffener inertia	I s = S 2 A st cm4
Symbols
= L, D and s are as defined in Pt 4, Ch 1, 1.5 Symbols and definitions 1.5.1 d c = vertical distance, in metres, between deck and horizontal stiffener on coaming or between horizontal stiffeners A st = area of stiffener including attached plating, in cm2 S = distance between coaming stiffeners, in metres L 1 = L but to be taken not less than 40 m I s = upper hatch coaming stiffener inertia
Note The scantlings of the topside structural parts may require to be increased to satisfy the hull girder bending stresses and buckling criteria inPt 3, Ch 4 Longitudinal Strength.

4.3.1 The thickness of the coaming is to comply with the requirements of Table 1.4.1 Topside structure (general) and is to be maintained over the length of the hatch opening. The plating thickness may, however, be reduced beyond 0,5L amidships in accordance with the requirements for taper given in Pt 3, Ch 3, 2.5 Principles for taper. Where coaming terminates at the end(s) of the hold, the combined taper area of the topside comprising coaming, deck and sheerstrake is to be used. As an alternative, direct calculations may also be used to prove that the allowable stresses given in Section 13 will not be exceeded. The thickness at the end of the hatch opening should, however, be not less than 80 per cent of the thickness amidships nor less than the minimum thickness required by Table 1.4.1 Topside structure (general)

4.3.2 The height of the hatch coaming is, in general, to be not more than 1,60 m above the deck and the hatch coaming is to extend at least 250 mm below the deck plating to provide for an efficient connection of the frame brackets and is to be substantially stiffened at the lower edge.

4.3.3 Coamings are to be stiffened at their upper edge by a substantial horizontal stiffener having scantlings complying with Table 1.4.1 Topside structure (general) The distance between the upper edge of the coaming and this stiffener is, generally, not to exceed 10 times the coaming thickness in way. If the height of the coaming is more than 1,0 m above deck, it is recommended to fit an additional horizontal stiffener halfway between the upper horizontal stiffener and the deck. Proposals to omit the longitudinal stiffener(s) are to be supported by additional buckling calculations.

4.3.4 Cut-outs in the upper edge of the coaming to accommodate hatchcovers are to be carefully designed and cut, with small rounded corners and be ground smooth after cutting. Hull girder bending stresses are to be calculated at the level of the lower edge of the cut-out.

4.3.5 Hatch coaming stays are to be fitted not more than 3 m apart. On ships regularly discharged by grabs, the distance between the stays is not to exceed 2 m.