Section
5 Single bottom structure and appendages
5.1 General
5.2 Keel
5.3 Centre girder
5.3.1 Centreline
girders are to be fitted throughout the length of each hull and are
generally to be fitted in association with transverse frames, transverses
supporting longitudinals or where the breadth of floors at the upper
edge is greater than 1,5 m.
5.3.2 Centreline
girders may be formed with intercostal or continuous plate webs. In
all cases the face flat is to be continuous. Where girder webs are
intercostal, additional bracketing and local reinforcement are to
be provided to maintain the continuity of structural strength.
5.3.3 The web
depth of the centre girder is, in general, to be equal to the depth
of the floors at the centreline as specified in Pt 6, Ch 4, 5.5 Floors 5.5.3.
5.3.9 The ratio
of the width to thickness of the face flat is to be not less than
eight but is not to exceed 16.
5.4 Side girders
5.4.1 Where the
floor breadth at the upper edge exceeds 4,0 m, side girders are to
be fitted at each side of the centre girder such that the spacing
between the side and centre girders or between the side girders themselves
is not greater than 2 metres. Side girders where fitted are to extend
as far forward and aft as practicable and are, in general, to be scarfed
into the bottom structure forward and aft of the support at which
they terminate, i.e. in way of bulkheads, deep floors or other primary
transverse structure.
5.4.6 In the
engineroom, additional side girders are generally to be fitted in
way of main machinery seatings. Where fitted they are to be integrated
into the structure of the craft and extended forward and aft as far
as practicable.
5.5 Floors
5.5.1 In transversely
framed craft, floors are generally to be fitted at every frame and
underneath each bulkhead.
5.5.2 In longitudinally
framed craft, floors are in general to be fitted at every transverse
web frame and bulkhead and generally at a spacing not exceeding 2
m. Additional transverse floors or webs are to be fitted at half web-frame
spacing in way of engine seatings and thrust bearings, pillars, skegs,
ballast/bilge keels and the bottom of the craft in the forefoot region.
5.5.5 If the
side frames of the craft are attached to the floors by brackets, the
depth of floor may be reduced by 15 per cent and the floor thickness
determined using the reduced depth. The brackets are to be flanged
and have the same thickness as the floors, and their arm lengths clear
of the frame are to be the same as the reduced floor depth given above.
5.5.7 The face
flat thickness, t
f, is to be not less than
the thickness of the web and the ratio of the web to the thickness
of the face flat is to be not less than eight but is not to exceed
16.
5.5.9 Floors
are in general to be continuous from side to side.
5.5.10 The tops
of floors, in general, may be level from side to side. However, in
craft having considerable rise of floor the depth of the floor plate
may require to be increased to maintain the required section modulus.
5.5.11 The floors in the aft peak are to extend over and provide efficient support
to the sterntube(s) where applicable.
5.6 Floors in machinery space
5.6.2 The depth
and mechanical strength properties of floors between engine or gearbox
girders is to be not less than that required to maintain continuity
of structural integrity or 50 per cent of the depth given in Pt 6, Ch 4, 5.5 Floors 5.5.3. The face flat area and web thickness
of such reduced height floors are to be increased appropriately in
order to maintain the continuity of structural strength, see
also
Pt 6, Ch 3, 4.12 Grouped frames.
5.7 Forefoot and stem
5.7.1 The thickness
of plate stems at the waterline is to comply with the requirements
for plate keels as given in Pt 6, Ch 4, 3.2 Keel plates.
5.7.2 The forefoot
and stem is to be additionally reinforced with floors.
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