Section
3 Watertight shell boundaries
3.1 General
3.1.1 The requirements of Chapter 7 regarding watertight
integrity are to be complied with.
3.1.2 The minimum requirements for watertight shell plating and framing of
column-stabilised units, self-elevating units, tension-leg units, buoys and deep
draught caissons are given in this Section.
3.1.3 The minimum requirements for watertight shell plating and framing of
surface type units are to comply with:
3.1.4 The Rules are, in general, applicable to shell plating with stiffeners
fitted parallel to the hull bending compressive stress. When other stiffening
arrangements are proposed, the scantlings are to be specially considered and the
minimum shell thickness is to satisfy the buckling strength requirements given in
Pt 4, Ch 5 Primary Hull Strength, but the minimum requirements of this
Section are to be complied with.
3.1.5 The shell plating thickness is to satisfy the requirements for the
overall strength of the unit in accordance with:
3.1.6 The scantlings of moonpool bulkheads will be specially considered with
regard to the maximum forces imposed on the structure and the permissible stress
levels are to comply with Pt 4, Ch 5 Primary Hull Strength.
3.1.10 The scantlings of circumturret well bulkheads on ship units are to
comply with Pt 10 Ship Units.
3.1.11 Where column structures or superstructures extend over the side shell of
the unit, the side shell/sheerstrake is to be suitably increased locally at the ends
of the structure.
3.1.12 On units fitted with two chines each side the bilge plating should not be
less than required for bottom plating. When units are fitted with hard chines the
shell plating is not to be flanged, but where the chine is formed by knuckling the
shell plating, the radius of curvature, measured on the inside of the plate, is not
to be less than 10 times the plate thickness. Where a solid round chine bar is
fitted, the bar diameter is to be not less than three times the thickness of the
thickest abutting plate. Where welded chines are used, the welding is to be built up
as necessary to ensure that the shell plating thickness is maintained across the
weld, see also
Pt 4, Ch 6, 3.4 Buoys and deep draught caissons 3.4.7.
3.1.13 The plating of swim ends is to have a thickness not less than that
required for bottom shell plating.
3.1.14 Where a rounded sheerstrake is adopted, the radius should, in general, be
not less than 15 times the plate thickness.
3.1.15 Sea inlets, or other openings, are to have well rounded corners and, so
far as possible, are to be kept clear of the bilge radius. Openings on, or near to,
the bilge radius are to be elliptical. The thickness of sea inlet box plating is to
be the same as the adjacent shell, but not less than 12,5 mm. The ends of stiffeners
should in general be bracketed and alternative proposals may be considered.
3.1.16 In general, secondary hull framing is to be continuous and the end
connections of stiffeners to watertight bulkheads are to provide adequate fixity
and, so far as practicable, direct continuity of strength.
3.1.17 The end connections of secondary hull framing and primary members are to
comply with:
3.1.19 Web frames supporting secondary hull framing are, in general, to be
spaced not more than 3,8 m apart when the length, L, is less than 100 m and
(0,006L + 3,2) m apart where L is greater than 100 m. For units
which are also required to operate aground, see
Pt 4, Ch 4, 2 Sea bed-stabilised units.
3.2 Column-stabilised and tension-leg
units
3.2.6 The shell plating and structure are to be reinforced in way of mooring
fairleads, supply boat moorings, towing brackets and other attachments, see
also
Pt 4, Ch 6, 1 General requirements.
3.2.7 Columns, lower hulls, footings and other areas likely to be damaged by
anchors, chain cables and wire ropes, etc., are to be protected or suitably
strengthened.
3.3 Self-elevating units
3.3.2 The shell plating thickness is to be suitably increased in way of high
shear forces in way of drilling cantilevers and other concentrated loads.
3.3.3 The scantlings and arrangements of the boundary bulkheads of leg wells
will be specially considered with regard to the maximum forces imposed on the
structure, and the permissible stress levels are to comply with Pt 4, Ch 5 Primary Hull Strength. The minimum scantlings are to comply with Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.4 as a tank bulkhead with the load head measured to the upper deck at side. In no case is the minimum
plating thickness to be less than 9 mm.
3.3.4 When cross ties are fitted inside pre-load tanks, the tensile stress in
the cross ties and its end connections is not to exceed 108 N/mm 2 (11,0
kgf/mm 2) at the test head, but the scantlings are also to comply with
the requirements of Pt 4, Ch 6, 3.3 Self-elevating units 3.3.5 and Pt 4, Ch 6, 3.3 Self-elevating units 3.3.6.
Table 6.3.1 Watertight shell
boundaries for lower hulls and columns of column-stabilised units and
tension-leg units
Items and
requirement
|
Boundaries of lower
hull or columns
|
(1) Shell plating thickness
See also
Pt 4, Ch 6, 3.1 General 3.1.5
|
t = 0,004s f
mm
but t +
tc not less than 7,5 mm
|
(2) Hull framing:
|
|
(a) Modulus
|
Z = 6,4 s k
ho
x 10-3 cm3
|
(b) Inertia
|
I =
Z cm4
|
(3) Primary members: Web
frames supporting framing:
|
|
(a)
Modulus
|
Z = 6,4 k ho S
cm3
|
(b)
Inertia
|
I =
Z cm4
|
Symbols
|
f = 1,1 – but not to be taken greater than 1,0
|
= load head in metres measured vertically as
follows:
|
(a) For shell plating the distance from a point
one-third of the height of the plate above its lower edge to a
point 1,4 above the keel or to the bottom of the upper
hull structure whichever is the lesser with a minimum of 6,0 m.
|
(b) For hull framing and primary members, the
distance from the middle of the effective length to a point 1,4 above the keel or to the bottom of the upper
hull structure whichever is the lesser with a minimum of 6,0 m.
|
k = steel factor as defined in Pt 4, Ch 2, 1 Materials of construction
|
= effective length of member, in metres, as
defined in Pt 4, Ch 3, 3.3 Determination of span point
|
s = spacing of frames, in mm
|
S = spacing or mean spacing of primary members, in metres
|
= maximum operating draught, in metres, as
defined in Pt 4, Ch 1, 5 Definitions
|
NOTES
|
1. In no case are the scantlings in way of tanks to
be less than the requirements given in Table 6.7.1 Watertight and deep tank
bulkhead scantlings for
tank bulkheads using the load head .
|
2. In no case are the scantlings to be less than the
requirements given in Table 6.7.1 Watertight and deep tank
bulkhead scantlings for
watertight bulkheads using the load head .
|
3. Where
frames are not continuous they are to be fitted with end
brackets in accordance with Pt 4, Ch 6, 7 Bulkheads or equivalent
arrangements provided.
|
3.3.5 When cross ties are fitted to support shell web frames the scantlings of
the web frames are to be determined from Table 6.3.4 Shell framing self-elevating
units and Table 6.7.1 Watertight and deep tank
bulkhead scantlings and the area and least moment of
inertia of the cross tie are to satisfy the following, see also
Pt 4, Ch 6, 3.3 Self-elevating units 3.3.6 and Pt 4, Ch 6, 3.3 Self-elevating units 3.3.7:
where
![](svgobject/EB04-4D9B-ACD1-05F98E45C850.xml_d9475800e1728.png) |
= |
length of cross tie between the toes of the horizontal brackets
on the web frames at the cross tie, in metres |
S |
= |
spacing of web frames, in metres |
![](svgobject/EB04-4D9B-ACD1-05F98E45C850.xml_d9475800e1831.png) |
= |
least inertia of cross tie cross-section, in cm4
|
![](svgobject/EB04-4D9B-ACD1-05F98E45C850.xml_d9475800e1875.png) |
= |
area of cross tie, in cm2
|
r |
= |
least radius of gyration of cross tie cross-section, in cm |
= |
![](svgobject/EB04-4D9B-ACD1-05F98E45C850.xml_d9475800e1926.png) |
as defined in Pt 4, Ch 3, 3.3 Determination of span point.
Figure 6.3.1 Cross tie construction
Table 6.3.2 Watertight shell boundaries of
the upper hull of column-stabilised units and tension-leg units
Items and
requirement
|
Boundaries of
upper hull
|
(1) Shell plating
thickness general
See also
Pt 4, Ch 3, 3.1 General 3.1.5
|
The greater of the
following:
|
(a)
t = 0,004sf
mm
|
(b)
t = 0,012
|
but
t + tc not less than 7,5 mm
|
(2) Bottom
plating thickness between columns within outside of column shell but not less than two web
frame spaces
See also
Pt 4, Ch 3, 3.1 General 3.1.5
|
The
greater of the following:
|
(a)
t = 0,004s f
mm
|
(b)
t = 0,012
|
but
t + tc not less than 7,5 mm
|
(3) Shell stiffeners and
primary webs, general
|
To comply with Table 6.7.1 Watertight and deep tank
bulkhead scantlings using the
load head
|
(4) Shell
stiffeners adjacent to columns as defined in (2):
|
|
(a)
Modulus
|
Z = 6,4 s k
x 10-3 cm3
|
(b)
Inertia
|
I =
Z cm4
|
Symbols
|
Symbols as defined in Table 6.7.1 Watertight and deep tank
bulkhead scantlings, except as
follows:
|
= load head, in metres, as defined in Table 6.7.1 Watertight and deep tank
bulkhead scantlings for
watertight bulkheads but not less than 6,0 m
|
= 470 + mm or 700, whichever is the smaller
|
= s but is not to be taken less than
|
W = greatest width or diameter of stability column, in metres
|
NOTES
|
In no case
are the scantlings in way of tanks to be less than the requirements
given in Table 6.7.1 Watertight and deep tank
bulkhead scantlings for tank
bulkheads using the load head .
|
3.3.6 The scantlings of the webs and flanges of cross ties are to be checked
for buckling by direct calculation.
3.3.7 Design of end connections of cross ties is to be such that the area of
the welding, including vertical brackets, where fitted, is to be not less than the
minimum cross sectional area of the cross tie derived from Pt 4, Ch 6, 3.3 Self-elevating units 3.3.5. To achieve this, full penetration welds may
be required and thickness of brackets may require further consideration. Attention
is to be given to the full continuity of area of the backing structure on the
transverses. Particular attention is also to be paid to the welding at the toes of
all end brackets on the cross tie.
3.4 Buoys and deep draught caissons
3.4.4 The shell plating and hull framing are to be reinforced in way of
mooring line attachments, mooring fairleads, supply boat moorings, towing brackets
and other attachments, see also
Pt 4, Ch 6, 1 General requirements.
3.4.5 Areas of the hull which may be damaged by chain cables or wire ropes are
to be protected or suitably strengthened.
3.4.7 Where cross ties are fitted inside tanks, the requirements of Pt 4, Ch 6, 3.3 Self-elevating units 3.3.4 are to be complied with.
Table 6.3.3 Shell plating self-elevating
units
Location
|
Thickness, in
mm, see also
Pt 4, Ch 3, 3.1 General 3.1.5
|
(1) Bottom shell
plating
|
|
See Notes 1 and 3
|
but t +
tc not less than 7,5 mm
|
(2) Bilge plating (framed)
See Note 2
|
t as for (1)
|
(3) Side shell plating
|
(a) Above from base:
|
See Notes 1, 2 and 3
|
|
|
(b) At upper turn
of bilge (see Note 1):
|
|
|
|
(c) Between upper turn of bilge
and from base:
|
|
The greater of the
following:
|
|
(i) t from (b)
|
|
(ii) t from
interpolation between (a) and (b)
|
Symbols
|
L, D,
, as defined in Pt 4, Ch 1, 5 Definitions
|
k = steel factor as defined in Pt 4, Ch 2, 1 Materials of construction
|
s = spacing of secondary stiffeners, in mm
|
= 470 + mm or 700 mm, whichever is the smaller
|
= s, but is not to be taken less than
|
Note 1. When no
bilge radius is fitted and the unit is fitted with hard chines,
the bottom shell thickness required by (1) is, in general, to be
extended up to ![](svgobject/EB04-4D9B-ACD1-05F98E45C850.xml_d9475800e3710.png) from base, see
Pt 4, Ch 6, 3.1 General 3.1.10.
|
Note 2. The
thickness of side shell need not exceed that determined from (1)
for bottom shell when using the spacing of side shell
stiffeners.
|
|
Table 6.3.4 Shell framing self-elevating
units
Items and
location
|
Modulus
|
(1) Hull framing, see
Note 1
|
|
(a) Bottom frames
|
Z = cm3
|
(b) Side frames
|
Z = cm3
|
(2) Primary members, see
Note 1
|
|
(a) Bottom web frames
supporting framing
|
Z = 6,4k
S
cm3
|
(b) Side web frames supporting
framing
|
Z = 6,4 k
S
cm3
|
Symbols
|
D and as defined in Pt 4, Ch 1, 5 Definitions
|
= load head, in metres, and is to be taken as the
distance from the middle of the effective length to a point 1,6 above the keel or to the upper deck at side
whichever is the lesser but not less than 0,01L + 0,7
|
k = steel factor as defined in Pt 4, Ch 2, 1 Materials of construction
|
= effective length of member, in metres, as
defined in Pt 4, Ch 3, 3.3 Determination of span point
|
s = spacing of frames, in mm
|
S = spacing or mean spacing of primary members, in
metres
|
NOTES
|
1. In no case are the scantlings in way of tanks to be less than
the requirements given in Table 6.7.1 Watertight and deep tank
bulkhead scantlings for tank
bulkheads using the load head .
|
2. In no case are the scantlings to be less than the
requirements given in Table 6.7.1 Watertight and deep tank
bulkhead scantlings for
watertight bulkheads using the load head .
|
3. Where frames are not continuous they are to be fitted with end
brackets in accordance with Pt 4, Ch 6, 7 Bulkheads or equivalent arrangements provided.
|
Table 6.3.5 Watertight shell boundaries of
buoys and deep draught caissons
Items and
requirement
|
Shell boundaries, see
Note 5
|
(1) Shell plating
thickness
|
t = 0,004sf
mm
|
See also
Pt 4, Ch 6, 3.1 General 3.1.5
|
but
t + tc not less than 7,5 mm
|
(2) Hull framing:
|
|
(a)
Modulus
|
Z = 6,4 s k
x 10-3 cm3
|
(b)
Inertia
|
I =
cm4
|
(3) Primary members: Web
frames supporting framing
|
|
(a)
Modulus
|
Z = 6,4 k
x 10-3 cm3
|
(b)
Inertia
|
I =
cm4
|
Symbols
|
f = 1,1 – but not to be taken greater than 1,0
|
= load head in metres measured vertically as
follows:
|
(a) For shell plating the distance from a point one third of the
height of the plate above its lower edge to the top of the highest
predicted wave in the most unfavourable design situation or to a
height 1,0 m above the uppermost deck, whichever is the greater with
a minimum of 6,0 m, see Note 3
|
(b) For hull framing and primary members, the distance from the
middle of the effective length to the top of the highest predicted
wave in the most unfavourable design situation or to a height 1,0 m
above the uppermost deck, whichever is the greater, with a minimum
of 6,0 m, see Note 3
|
k = steel factor as defined in Pt 4, Ch 2, 1 Materials of construction
|
= effective length of member in metres as defined
in Pt 4, Ch 3, 3.3 Determination of span point
|
s = spacing of frame in mm
|
S = spacing or mean spacing of primary members, in metres
|
NOTES
|
1. In no case are the scantlings in way of tanks to be less than
the requirements given in Table 6.7.1 Watertight and deep tank
bulkhead scantlings for tank bulkheads using the load
head .
|
2. In no case are the scantlings to be less than the
requirements given in Table 6.7.1 Watertight and deep tank
bulkhead scantlings for watertight bulkheads using the
load head .
|
3a. For shell plating of units defined in Pt 3, Ch 13 Buoys, Deep Draught Caissons, Turrets and Special Structures which are designed to
follow the wave profile, need not exceed the distance measured from a
point one third of the height of the plate above its lower edge to
the top of the highest predicted wave in the most unfavourable
design situation or to a height 1,0 m above the uppermost deck,
whichever is the greater. (But note that t shall not be less
than 9,0 mm.)
|
3b. For hull framing of units defined in Pt 3, Ch 13 Buoys, Deep Draught Caissons, Turrets and Special Structureswhich are designed to
follow the wave profile, need not exceed the distance measured from the
middle of the effective length to the top of the highest predicted
wave in the most unfavourable design situation or to a height 1,0 m
above the uppermost deck, whichever is the greater, but shall not be less than the calculated from the shell plating thickness
formulation (Table 6.3.5 Watertight shell boundaries of
buoys and deep draught caissons (1)) that corresponds to the
minimum thickness requirement of 9,0 mm.
|
4. Where frames are not continuous they are to be fitted
with end brackets in accordance with Pt 4, Ch 6, 7 Bulkheads or equivalent arrangements
provided.
|
5. The scantlings of shell boundaries derived from this Table are
to be suitably increased in way of tanks which cannot be inspected
at normal periodic surveys, see
Pt 4, Ch 4, 7.10 Corrosion protection.
|
|