(1) The coamings of hatchways closed by portable
covers secured weathertight by tarpaulins and battening devices shall
be of substantial construction, and their height above the deck shall
be at least as follows:
(2) The width of each bearing surface for hatchway
covers shall be at least 65 millimetres (2½ inches).
(3) Where covers are made of wood, the finished
thickness shall be at least 60 millimetres (2⅜ inches) in association
with a span of not more than 1.5 metres (4.9 feet).
(4) Where covers are made of mild steel the strength
shall be calculated with assumed loads not less than 1.75 metric tons
per square metre (358 pounds per square foot) on hatchways in position
1, and not less than 1.30 metric tons per square metre (266 pounds
per square foot) on hatchways in position 2, and the product of the
maximum stress thus calculated and the factor 4.25 shall not exceed
the minimum ultimate strength of the material. They shall be so designed
as to limit the deflection to not more than 0.0028 times the span
under these loads.
(5) The assumed loads on hatchways in position
1 may be reduced to 1 metric ton per square metre (205 pounds per
square foot) for ships of 24 metres (79 feet) in length and shall
be not less than 1.75 metric tons per square metre (358 pounds per
square foot) for ships of 100 metres (328 feet) in length. The corresponding
loads on hatchways in position 2 may be reduced to 0.75 metric tons
per square metre (154 pounds per square foot) and 1.30 metric tons
per square metre (266 pounds per square foot) respectively. In all
cases values at intermediate lengths shall be obtained by linear interpolation.
(6) Where portable beams for supporting hatchway
covers are made of mild steel the strength shall be calculated with
assumed loads not less than 1.75 metric tons per square metre (358
pounds per square foot) on hatchways in position 1 and not less than
1.30 metric tons per square metre (266 pounds per square foot) on
hatchways in position 2 and the product of the maximum stress thus
calculated and the factor 5 shall not exceed the minimum ultimate
strength of the material. They shall be so designed as to limit the
deflection to not more than 0.0022 times the span under these loads.
For ships of not more than 100 metres (328 feet) in length the requirements
of paragraph (5) of this Regulation are applicable.
(7) Where pontoon covers used in place of portable
beams and covers are made of mild steel the strength shall be calculated
with the assumed loads given in paragraph (4) of this Regulation,
and the product of the maximum stress thus calculated and the factor
5 shall not exceed the minimum ultimate strength of the material.
They shall be so designed as to limit the deflection to not more than
0.0022 times the span. Mild steel plating forming the tops of covers
shall be not less in thickness than one per cent of the spacing of
stiffeners or 6 millimetres (0.24 inches) if that be greater. For
ships of not more than 100 metres (328 feet) in length the requirements
of paragraph (5) of this Regulation are applicable.
(8) The strength and stiffness of covers made
of materials other than mild steel shall be equivalent to those of
mild steel to the satisfaction of the Administration.
(9) Carriers or sockets for portable beams shall
be of substantial construction, and shall provide means for the efficient
fitting and securing of the beams. Where rolling types of beams are
used, the arrangements shall ensure that the beams remain properly
in position when the hatchway is closed.
(10) Cleats shall be set to fit the taper of the
wedges. They shall be at least 65 millimetres (2½ inches) wide
and spaced not more than 600 millimetres (23½ inches) centre
to centre; the cleats along each side or end shall be not more than
150 millimetres (6 inches) from the hatch corners.
(11) Battens and wedges shall be efficient and
in good condition. Wedges shall be of tough wood or other equivalent
material. They shall have a taper of not more than 1 in 6 and shall
be not less than 13 millimetres (½ inch) thick at the toes.
(12) At least two layers of tarpaulin in good
condition shall be provided for each hatchway in position 1 or 2.
The tarpaulins shall be waterproof and of ample strength. They shall
be of a material of at least an approved standard weight and quality.
Security of Hatchway Covers
(13) For all hatchways in position 1 or 2 steel
bars or other equivalent means shall be provided in order efficiently
and independently to secure each section of hatchway covers after
the tarpaulins are battened down. Hatchway covers of more than 1.5
metres (4.9 feet) in length shall be secured by at least two such
securing appliances.