Article 5 Hatchway covers
Subject to paragraph (2) of this Rule, in every vessel of 12 metres in length and over to which these Rules apply where hatchway covers are constructed of wooden boards with waterproof covers—
the unsupported span of the wooden boards shall not exceed 1.5 metres;
the finished thickness of the wooden boards shall be not less than 4 millimetres for each 100 millimetres of unsupported span and the width of their bearing surfaces shall not be less than 65 millimetres, except that no wooden board shall have a finished thickness of less than 40 millimetres;
a waterproof cover of suitable material and of adequate strength shall be provided for every hatchway and be capable of being secured in place in accordance with sub-paragraphs (e) and (f) below;
where portable beams are provided to support hatchway covers the strength of such beams shall be calculated using the assumed static loads given in sub-paragraph (3)(a) below and the mechanical properties of the material used in the construction and such beams shall be of adequate strength for their intended service;
cleats shall be set to fit the taper of the wedges, spaced 600 millimetres centre to centre and at least 65 millimetres wide. The end cleats on each end or side shall be not more than 150 millimetres from the hatch corners;
an adequate number of battens and wedges of efficient pattern and in good condition shall be provided. The wedges shall be of tough wood or equivalent material cut to a taper of not more than 1 in 6 and shall not be less than 12 millimetres thick at the toes;
steel bars shall be provided to ensure that each section of the hatchway covers can be efficiently and independently secured after the waterproof covers have been battened down;
hatchway covers shall be permanently marked to indicate their correct position.
In any such vessel less than 24.4 metres in length other arrangements equally effective to the requirements of sub-paragraphs (1)(c), (e), (f) and (g) of this Rule may be provided to maintain wooden hatch covers in position and secure them weathertight.
In every vessel of 12 metres in length and over to which these Rules apply where hatchway covers are constructed of material other than wood:—
for the purpose of strength calculations it shall be assumed that such covers are subjected to the weight of cargo intended to be carried on them or to the following static loads whichever is the greater:—
1.0 tonne per square metre, where the length of the vessel is 24.4 metres or less;
1.75 tonnes per square metre, where the length of the vessel is 100 metres or more.
For vessels of lengths more than 24.4 metres but not exceeding 100 metres the loads shall be determined by linear interpolation provided that where a hatchway is situated on the superstructure deck in a position abaft a point 0.25 of the Principal Length from the forward perpendicular, the assumed loads may be reduced to not less than 75% of the requirement of this paragraph;
where such covers are constructed of mild steel, the maximum stress calculated using the assumed static loads set out in sub-paragraph (a) above when multiplied by 4.25 shall not exceed the minimum ultimate strength of the material. Under these loads the deflections shall not be more than 0.0028 times the span;
every such cover constructed of material other than mild steel shall have strength and stiffness equivalent to those required in the case of a cover of mild steel;
every such cover shall be fitted with gaskets and clamping devices, or other equally effective arrangements, sufficient to ensure weather-tightness.