Figure B.5 Midship section of 28,400 DWT ship with round wood secured
with uprights
Ship particulars
|
|
Length between perpendiculars,
LPP:
|
160 metres
|
|
|
Moulded breadth, BM:
|
27 metres
|
|
|
Service speed:
|
14 knots
|
|
|
Metacentric height, GM:
|
0.80 metres
|
The deck cargo has the dimensions L x B x H = 110 x 25.6 x 7 metres and is
supported by 42 uprights on each side. The total weight is taken as 10,500 tons.
In addition to the uprights and hog-lashings, the cargo has been secured
with top-over lashings applied in accordance with sections 5.4 and 6.5.28 – 6.5.30 .
With ship particulars as above and considering a stowage position on deck
low, Annex
13 of the CSS Code gives a transverse acceleration of at
= 4.6 m/s2
, using the following basic acceleration and correction factors:
|
at
basic
|
=
|
6.5 m/s2
|
=
|
Basic
transverse acceleration
|
|
fR1
|
=
|
0.71
|
=
|
Correction factor for length and speed
|
|
fR
2
|
=
|
1.00
|
=
|
Correction factor for BM/GM
|
|
a t
|
= |
|
Cargo properties
|
M
|
=
|
10,500 ton
|
=
|
Mass of
the section to be secured in tons, including absorbed water and possible
icing
|
|
μstatic
|
=
|
0.35
|
=
|
Coefficient of static friction between the timber deck cargo and the ship's
deck/hatch cover
|
|
H
|
=
|
7 m
|
=
|
Height
of deck cargo in metres
|
|
B
|
=
|
25.6 m
|
=
|
Width of
deck cargo in metres
|
|
L
|
=
|
110 m
|
=
|
Length
of the deck cargo or section to be secured in metres
|
|
PW
|
=
|
770 kN
|
=
|
Wind
pressure in kN based on 1 kN per m2 wind exposed area, see CSS
Code, Annex 13
|
|
PS
|
=
|
220 kN
|
=
|
Pressure
from unavoidable sea sloshing in kN based on 1 kN per m2 exposed
area, see CSS Code, Annex 13
|
|
N
|
=
|
42 pcs
|
=
|
Number of
uprights supporting the considered section on each side
|
|
h
|
=
|
3.7 / m
6.7
|
=
|
Height
above deck at which hog lashings are attached to the uprights in
metres
|
|
nhog
|
=
|
2 pcs
|
=
|
Number
of hog lashings for each upright
|
|
k
|
=
|
1.8
|
=
|
Factor
for considering hog lashings;
|
|
|
|
|
|
|
k = 1 if no hog lashings
are used
|
|
|
|
|
|
|
k = 1.8 if hog lashings
are used
|
Bending moment in uprights
For ships carrying loose sawn wood and round wood, the design bending
moment per upright is calculated as the greater of the two moments given by the
following formulas:
With cargo properties and acceleration as given above, the following
bending moments are calculated:
|
CM bending1
|
= |
|
| = |
260 kNm
|
|
CM bending 2
|
= |
|
| = |
854 kNm
|
The design bending moment, taken as the maximum bending moment calculated by
the formulae above multiplied with a safety factor of 1.35 and considering the 12%
reduction allowed for by the use of properly applied top-over lashings, thus
becomes:
- M bending
≥
|
|
= |
0.88•1.35•854 |
| = |
1015 kNm
|
Suitable dimensions for uprights
With MSL taken as 50% of the MBL for steel with the ultimate strength 360 MPa
(N/mm2), the required bending resistance, W, can be calculated as:
|
W
|
= |
|
| = |
|
| = |
5639•103
mm
3
|
| = |
5639 cm
3
|
Thus, uprights made from either HE 600 B profiles or a cylindrical profile
with an outer diameter of 610 mm and a wall thickness of 24.6 mm are suitable (see section
B.7).
Strength in hog lashings
The required MSL of each hog lashing is calculated by the following
formula:
In this case, the hog lashings are attached at the heights 3.7 and 6.7
metres (mean height=5.2) and the required strength is calculated as:
- MSL ≥
= 
= 49 kN ≈ 4.9 ton