7.1.1 Requirements
are given in this Section for single bottom construction in association
with transverse framing, and are generally applicable to the following
ships:
-
Cargo ships of
less than 500 tons gross tonnage,
-
Ships not propelled
by mechanical means, and
-
Trawlers and fishing
vessels.
Cases where a single bottom structure is adopted in association
with longitudinal framing will be considered.
7.1.2 Ships
with single bottoms are to have a centre girder fitted. In addition,
one side girder is to be fitted on each side of the centreline where B does not exceed 10 m, and two side girders on each side where B is greater than 10 m and does not exceed 17 m. In addition,
continuous or intercostal longitudinal stiffeners are to be fitted
where the panel size exceeds the ratio 4 to 1. Centre and side girders
are to extend as far forward and aft as practicable, and where they
cut at bulkheads the longitudinal strength is to be maintained.
7.1.3 Plate
floors are to be fitted at every frame, and the tops of floors, in
general, may be level from side to side, but in ships having considerable
rise of floor, and towards the ends, the depth of the floor plates
is to be increased. Floor plates forming part of a watertight or deep
tank bulkhead are to be not less than 900 mm in depth measured at
the centreline, and the thickness is to be not less than that required
for the bottom strake of a bulkhead.
7.1.4 For
ships intended to load or unload while aground, see
Pt 3, Ch 9, 7 Bottom strengthening for loading and unloading aground.
Table 1.7.1 Single bottom girders and
floors
| Item
|
Depth, in mm
|
Thickness, in mm
|
Face
plate area, in cm2
|
|
(1) Centre girder
|
As for
floors
|
but not less than 6,0
|
A
f = 0,67Lk
but not less than 12,5
See Notes 2 and
3
|
|
(2) Side girders
|
As for
floors
|
but not less than 6,0
|
A
f = (0,25L+ 5)k
but not less than 10,0
See Note 3
|
|
(3) Floors
|
Where B ≤ 10 m
|
d
f = 40 (B + T)
|
but not less than 6,0
|
See Notes 2 and 3
|
|
|
Where B > 10
m
(see Note 1)
|
d
f = 40 (1,5B + T) – 200
|
| Symbols
|
|
b
f
|
= |
breadth of face plate, in mm |
|
d
f
|
= |
overall depth of floor at the centreline, in mm |
|
|
s
1
|
= |
a standard frame spacing, in mm, and is to be taken
as
2 (L + 240) |
|
A
f
|
= |
cross-sectional area of face plate, in cm2
|
|
Note
1. If the side frames are attached to the
floors by brackets, the Rule 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 and are to be the same as the
reduced floor depth given above.
Note
2. The face plate thickness of floors and
centre girder is to be not less than the floor plate thickness.
Note
3. The thickness of face plates is to be:
not less than  nor more than 
|
7.1.5 Provision
is made for the free passage of water from all parts of the bottom
to the suctions, taking into account the pumping rates required.