5 External Pressures on Hatch Covers

5.1 Application

5.1.1 The external pressures on hatch covers are only to be applied for strength assessment.

5.2 Green sea loads

5.2.1 The green sea loads at any load point of a hatch cover, P_HC, in kN/mm², is to be taken as follows:

For cargo hold analysis according to Ch 7:
- P_HC = P_D – ρ g (z_HC – D) without being less than 0.
For other cases: P_HC = P_D,min as defined in Table 30.

P_D : Green sea pressure, in kN/mm², on the deck in way of the hatch cover obtained according to [2.2], considering χ equal to 1.0.

z_HC : z coordinate of the top of the hatch cover, in m.

5.3 Load carried on hatch covers

5.3.1 If a distributed load or a unit load is carried on a hatch cover, the pressure is to be obtained according to [2.3].

Table 33 : Coefficient f_n

Type of bulkhead	Location	*f_n*
Unprotected front bulkhead ⁽¹⁾	Lowest tier ⁽²⁾
	Second tier
	Third tier and above
Protected front bulkhead ⁽¹⁾	All tiers
Side bulkheads	All tiers
Aft end bulkheads	Abaft amidships
Aft end bulkheads	Forward of amidships
(1) The front bulkhead of a superstructure or deckhouse may be considered as protected when it is located less than B_x behind another superstructure or deckhouse, and the width of the front bulkhead being considered is less than the width of the aft bulkhead of the superstructure or deckhouse forward of it. B_x is the local breadth of the ship at the front bulkhead. (2) The lowest tier is normally that tier which is directly situated above the uppermost continuous deck to which the moulded depth D is measured. However, when (D - T_SC) exceeds the minimum non-corrected tabular freeboard (according to ICLL as amended) by at least one standard superstructure height (as defined in Ch 1, Sec 4, [3.3]), then this tier may be defined as the 2^nd tier and the tier above as the 3^rd tier.

Table 34 : Coefficient f_b

Location of bulkhead ⁽¹⁾

f_b

where:

C_B1 : Block coefficient, but not less than 0.60 nor greater than 0.80. For aft deckhouse bulkheads located forward of amidships, C_B1 may be taken as 0.80.

(1) For deckhouse sides, the deckhouse is to be subdivided into parts of approximately equal length, not exceeding 0.15L each, and x is to be taken as the X-coordinate of the centre of each part considered.

Table 35 : Minimum lateral pressure, P_A-min

	P_A-min, in kN/m²
L	Lowest tier of unprotected fronts	Elsewhere ⁽¹⁾
90 < L ≤ 250
L > 250	50	25
(1) For the 4^th tier and above, P_A-min is to be taken equal to 12.5 kN/m².

5 External Pressures on Hatch Covers

Table 33 : Coefficient fn

Table 34 : Coefficient fb

Table 35 : Minimum lateral pressure, PA-min

Table 33 : Coefficient f_n

Table 34 : Coefficient f_b

Table 35 : Minimum lateral pressure, P_A-min