Example B.5.2 – Midship section of 16 600 DWT ship with round wood secured with
uprights
Ship particulars
| Length between
perpendiculars, LPP:
|
134 metres
|
| Moulded breadth,
BM:
|
22 metres
|
| Service speed:
|
14.5 knots
|
| Metacentric height, GM:
|
0.70 metres
|
The deck cargo has the dimensions L x B x H = 80 x 19.7 x 3.7 metres and is
supported by 30 uprights on each side. The weight of the cargo is taken as 3,000
tons.
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
= 5.3 m/s2
, using the following basic acceleration and correction factors:
|
at
basic
|
=
|
6.5 m/s2
|
=
|
Basic
transverse acceleration
|
|
fR1
|
=
|
0.81
|
=
|
Correction factor for length and speed
|
|
fR
2
|
=
|
1.00
|
=
|
Correction factor for BM/GM
|
|
a t
|
= |
|
| = |
6.5 • 0.81 • 1.00 |
| = |
5.3 m / s2
|
Cargo properties
|
M
|
=
|
3,000 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
|
=
|
3.7 m
|
=
|
Height of
deck cargo in metres
|
|
B
|
=
|
19.7 m
|
=
|
Width of
deck cargo in metres
|
|
L
|
=
|
80 m
|
=
|
Length
of the deck cargo or section to be secured in metres
|
|
PW
|
=
|
296 kN
|
=
|
Wind
pressure in kN based on 1 kN per m2 wind exposed area, see CSS
Code, Annex 13
|
|
PS
|
=
|
160 kN
|
=
|
Pressure
from unavoidable sea sloshing in kN based on 1 kN per m2 exposed
area, see CSS Code, Annex 13
|
|
N
|
=
|
30 pcs
|
=
|
Number of
uprights supporting on each side
|
|
h
|
=
|
3.7 m
|
=
|
Height
above deck at which hog lashings are attached to the uprights in
metres
|
|
nhog
|
=
|
1 pcs
|
=
|
Number of
hog lashings for each uprights
|
|
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 timber, 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
|
= |
|
| = |
68 kNm
|
|
CM bending2
|
= |
|
| = |
209 kNm
|
The design bending moment, taken as the maximum bending moment calculated by
the formulae above multiplied with a safety factor of 1.35, thus becomes 282 kNm:
- M bending
≥
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
|
= |
|
| = |
|
| = |
1568•103
mm
3
|
| = |
1568 cm
3
|
Thus, uprights made from either HE320B profiles or a cylindrical profile
with an outer diameter of 406 mm and a wall thickness of 16.7 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 a height of 3.7 metres and
the required strength is calculated as:
- MSL ≥
= 
= 38 kN ≈ 3.9 ton