Figure B.7 Midship section of 6,000 DWT ship with round wood secured
with uprights
Ship particulars
| Length between perpendiculars,
LPP:
|
101 metres
|
| Moulded breadth, BM:
|
17.5 metres
|
| Service speed:
|
13 knots
|
| Metacentric height, GM:
|
0.50 metres
|
The deck cargo has the dimensions L x B x H = 65 x 14.5 x 3.1 metres and is
supported by 25 uprights on each side. The weight of the cargo is taken as 1,500
tons.
With ship particulars as above and considering a stowage position on deck
low,
Annex 13 of the CSS Code gives the following basic transverse acceleration and
correction factors:
|
at
basic
|
=
|
6.5 m/s2
|
=
|
Basic
transverse acceleration
|
|
fR1
|
=
|
0.93
|
=
|
Correction factor for length and speed
|
|
fR
2
|
=
|
1.00
|
=
|
Correction factor for BM/GM
|
The ship is trading in the Baltic Sea with a weather forecast predicting a
significant wave height up to 5.5 meters. Thus, the reduction factor for operation in
restricted waters is taken as:
- fR = 1 - (Hs - 13)2 / 240 = 1 - (5.5 -
13)2 / 240 = 0.76
|
at
|
= |
|
| = |
6.5•0.93•1.00•0.76 |
| = |
4.6 m / s2
|
Cargo properties
| M
|
=
|
1,500 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
|
=
|
3.1 m
|
=
|
Height
of deck cargo in metres
|
| B
|
=
|
14.5 m
|
=
|
Width of
deck cargo in metres
|
| L
|
=
|
65 m
|
=
|
Length of
the deck cargo or section to be secured in metres
|
| PW
|
=
|
202 kN
|
=
|
Wind
pressure in kN based on 1 kN per m2 wind exposed area, see CSS
Code, Annex 13
|
| PS
|
=
|
130 kN
|
=
|
Pressure
from unavoidable sea sloshing in kN based on 1 kN per m2 exposed
area, see CSS Code, Annex 13
|
| N
|
=
|
25 pcs
|
=
|
Number of
uprights supporting the considered section on each side
|
| h
|
=
|
3.1 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
|
= |
|
| = |
39 kNm |
|
CM bending2
|
= |
|
| = |
95 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 128 kNm:
M bending
≥ 
= 1.35•95 = 128 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
|
= |
|
| = |
|
| = |
713•103
mm
3
|
| = |
713 cm
3
|
Thus, uprights made from either HE220 B profiles or a cylindrical profile
with an outer diameter of 324 mm and a wall thickness of 10 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 m and the
required strength is calculated as:
MSL ≥ 
= 
= 20.6 kN ≈ 2.1 ton