Section
5 Single bottom structure and appendages
5.1 General
5.1.2 The minimum
thickness requirements detailed in Pt 8, Ch 4, 2.1 General are
to be complied with as appropriate.
5.2 Keel
5.2.1 The scantlings
and arrangements of plate keels are to be in accordance with Pt 8, Ch 4, 3.2 Keel plates. Where it is proposed to incorporate
keels of the bar type such arrangements would require to be specially
considered.
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 top hat or plate
webs. Where girder webs are intercostal, additional bracketing and
local reinforcement as given in Pt 8, Ch 3, 3.14 Local reinforcement are
to be provided to maintain the continuity of structural strength.
The face reinforcement in all cases is to be continuous.
5.3.3 The web
depth of the centre girder in general is to be equal to the depth
of the floors at the centreline as specified in Pt 8, Ch 4, 5.5 Floors.
5.3.6 The face
area of the centre girder, A
f, is to be not
less than:
5.3.8 The face
thickness, t
f, is to be not less than the
web thickness of the centre girder.
5.4 Side girder
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 3 m. Side girders where fitted are to extend as
far forward and aft as practicable and are in general to terminate
in way of bulkheads, deep floors or other primary transverse structure.
5.4.2 In the
engine room, additional side girders are generally to be fitted in
way of the main machinery.
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 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.
5.5.3 The overall
depth of transverse floors at the centreline, d
W,
is not to be taken as less than:
5.5.5 The web thickness for transverse
floors of single plate laminate construction is to be two times the
thickness as required by Pt 8, Ch 4, 5.5 Floors 5.5.4.
5.5.6 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 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.
5.5.8 The thickness
of the face laminate, t
f, is to be not less
than the web thickness.
5.5.10 Floors
are generally to be continuous from side to side.
5.5.11 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 mechanical properties
of the section.
5.5.12 The floors
in the aft peak are to extend over and provide efficient support to
the stern tube(s) where applicable.
5.6 Floors in machinery space
5.6.1 The depth
and mechanical 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 8, Ch 4, 5.5 Floors 5.5.3. The web thickness and face reinforcement
weight of such reduced height floors are to be increased appropriately
in order to maintain the continuity of structural strength.
5.7 Lower hull (SWATH)
5.7.1 Where the
lower hull structure incorporates ring frames and attached shell laminate
fitted between bulkheads or diaphragms, the scantlings of the lower
hull shell stiffening may be derived from an established method for
stiffening analysis or recognised standard for pressure vessels. Modes
of failure to be considered are buckling, frame collapse, inter frame
shell collapse and overall frame shell collapse between bulkheads.
Copies of detailed calculations are to be submitted for consideration.
5.7.2 In general,
the design load used is to be the design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or
displacement craft as appropriate. If other loads are considered to
be of significance for the scantling determination these are to be
taken into account.
5.8 Forefoot and stem
5.9 Transom knee
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