(1) A trunk or similar structure which does not
extend to the sides of the ship shall be regarded as efficient on
the following conditions:
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(a) the trunk is at least as strong as a superstructure;
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(b) the hatchways are in the trunk deck, the hatchway
coamings and covers comply with the requirements of regulations 13 to 16 inclusive and the width of the trunk
deck stringer provides a satisfactory gangway and sufficient lateral
stiffness. However, small access openings with watertight covers may
be permitted in the freeboard deck;
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(c) a permanent working platform fore and aft
fitted with guard rails is provided by the trunk deck, or by detached
trunks connected to superstructures by efficient permanent gangways;
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(d) ventilators are protected by the trunk, by
watertight covers or by other equivalent means;
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(e) open rails are fitted on the weather parts
of the freeboard deck in way of the trunk for at least half their
length or, alternatively, freeing port area in the lower part of the
bulwarks, subject to regulation 24(2),
of 33% of the total area of the bulwarks is provided;
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(f) the machinery casings are protected by the
trunk, by a superstructure of at least standard height, or by a deckhouse
of the same height and of equivalent strength;
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(g) the breadth of the trunk is at least 60% of
the breadth of the ship; and
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(h) where there is no superstructure, the length
of the trunk is at least 0.6L.
(2) The full length of an efficient trunk reduced
in the ratio of its mean breadth to B shall be its effective length.
(3) The standard height of a trunk is the standard
height of a superstructure other than a raised quarter deck.
(4) Where the height of a trunk is less than the
standard height, its effective length shall be reduced in the ratio
of the actual to the standard height. Where the height of hatchway
coamings on the trunk deck is less than that required under regulation 14-1, a reduction from the actual
height of trunk shall be made which corresponds to the difference
between the actual and the required height of coaming.
(5) Where the trunk height is less than standard
and the trunk hatch coamings are also of less than standard height,
or omitted entirely, the reduction from the actual height of trunk
on account of insufficient hatch coaming height shall be taken as
the difference between 600 mm and the actual height of coaming, or
600 mm if no hatch coamings are fitted. Reduction in the actual height
of trunk shall not be required in cases where only small hatches with
less than standard height are fitted in the trunk deck for which dispensation
from the requirement of standard coaming height may be given.
(6) Continuous hatchways may be treated as a trunk
in the freeboard computation, provided the provisions of this paragraph
are complied with in all respects.
The trunk deck stringer referred to in paragraph (1)(b)
may be fitted outboard of the trunk side bulkhead in association with
the following:
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(a) the stringer so formed is to provide a clear
walkway of at least 450 mm in width on each side of the ship;
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(b) the stringer is to be of solid plate, efficiently
supported and stiffened;
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(c) the stringer is to be as high above the freeboard
deck as practicable. In the freeboard calculation, the trunk height
is to be reduced by at least 600 mm or by the actual difference between
the top of the trunk and the stringer, whichever is greater;
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(d) hatch cover securing appliances are to be
accessible from the stringer or walkway; and
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(e) the breadth of the trunk is to be measured
between the trunk side bulkheads.
(7) Where the trunk adjoining the superstructures
such as poop, bridge or forecastle is included in the calculation
of freeboard, openings shall not be arranged in that part of the bulkhead
which is common for the trunk and superstructure. A relaxation may
be made for small openings such as for piping, cable or manholes with
covers attached by means of bolts.
(8) The sides of a trunk included in the calculation
of freeboard shall be intact. Side scuttles of the non-opening type
and bolted manhole covers may be allowed.