Section
9 Strengthening for machinery on deck
9.1 Application
9.1.1 Where it is intended to install machinery on deck, the requirements of this Section
are to be complied with and the notation ‘Machinery on deck’ will be
assigned.
9.1.2 Where the concentrated loads calculated in accordance with Pt 3, Ch 9, 9.2 Loading are less than the specified deck
design load required by Table 3.5.1 Design heads and permissible cargo
loadings or where the ship has been assigned a ‘Heavy deck
loads’ notation and the machinery loading is less than the assigned heavy
deck cargo loading, then the requirements of this Section need not be applied and
the notation will not be assigned.
9.1.3 The requirements of this Section do not apply to lifting appliances, anchoring and
mooring equipment, or towing equipment.
9.2 Loading
9.2.1 The motions of the ship and the wind loading are to be considered in
deriving the loads acting on the ship.
9.2.2 The design accelerations are to be calculated in accordance with Pt 3, Ch 9, 9.2 Loading 9.2.3 and applied as considered necessary.
Other means of deriving the design accelerations such as direct calculation or model
testing will be specially considered.
9.2.3 The following formulae are given as guidance for the components of
acceleration due to ship motions and apply to ships with a length exceeding 50
metres and where the speed is such that the ship is operating within the
displacement mode based on normal ship service speed.
Vertical acceleration due to heave, pitch and roll
motions:
Transverse acceleration due to sway, yaw and roll
motions:
Longitudinal acceleration due to surge motions:
Where:
|
A |
= |
 |
|
ax, ay and
az |
= |
are the maximum dimensionless accelerations (i.e. relative
to the acceleration of gravity) in their respective directions and are
considered as acting separately for calculation purposes. |
|
ax |
= |
is measured positive in the forward direction. Includes the
component due to static weight in the longitudinal direction due to
pitching. |
|
ay |
= |
is measured positive in the transverse direction to port.
Includes the component due to static weight in the transverse direction
due to rolling. |
|
az |
= |
is measured positive in the downwards direction, i.e. adds
to g. Does not include the component due to static weight. |
a0, aheave, apitch,
asway, ayaw,
arolly, a(rollz),
fst and A are defined in Table 9.9.1 Ship motions.
|
fHS |
= |
1 for unrestricted sea going service |
| = |
0,8 for restricted service |
| = |
0,5 for sheltered waters/harbour conditions |
|
T, L and Cb |
= |
are defined in Pt 3, Ch 1, 6.1 Principal particulars |
|
z |
= |
is the vertical distance, in metres, from the keel line to
the position or centre of gravity of the item being considered. |
9.2.5 The wind pressure, p, acting on the structure is given by:
Where:
|
V |
= |
wind speed, in m/s; to be taken as 63 m/s. |
9.2.6 The wind force, Fw, acting on the structure is given by:
Where:
|
A |
= |
the effective area of the structure concerned, i.e. the solid area
projected on to a plane perpendicular to the wind direction, in
m2 |
|
p |
= |
the wind pressure as defined in Pt 3, Ch 9, 9.2 Loading 9.2.5
|
|
Cf |
= |
the force coefficient in the direction of the wind, as
defined in Table 9.9.2 Force coefficient
Cf |
Table 9.9.2 Force coefficient
Cf
| Type
|
Description
|
Aerodynamic slenderness l/b or l/D
|
| 5
|
10
|
20
|
30
|
40
|
50
|
| Individual
members
|
Rolled sections, rectangles, hollow sections, flat plates, box
sections with b or d less than 0,5 m
|
1,30
|
1,35
|
1,60
|
1,65
|
1,70
|
1,80
|
| Circular
sections, where
|
DVs < 6 m2/s
|
0,75
|
0,80
|
0,90
|
0,95
|
1,00
|
1,10
|
| DVs ≥ 6 m2/s
|
0,60
|
0,65
|
0,70
|
0,70
|
0,75
|
0,80
|
| Box sections with b or d greater than 0,5
m
|
b/d
|
|
|
|
|
|
|
| ≥2,00
|
1,55
|
1,75
|
1,95
|
2,10
|
2,20
|
|
| 1,00
|
1,40
|
1,55
|
1,75
|
1,85
|
1,90
|
|
| 0,50
|
1,00
|
1,20
|
1,30
|
1,35
|
1,40
|
|
| 0,25
|
0,80
|
0,90
|
0,90
|
1,00
|
1,00
|
|
| Single lattice
frames
|
Flat
sided sections
|
1,70
|
| Circular
sections, where
|
DVs < 6 m2/s
|
1,20
|
| DVs ≥ 6 m2/s
|
0,80
|
| Plated structure
|
Plated structures on solid base (air flow beneath structure
prevented)
|
1,10
|
| Symbols
|
|
l |
= |
length of member |
|
D |
= |
diameter of circular section |
|
Vs |
= |
wind speed, in m/s |
|
b |
= |
breadth of box section, in metres |
|
d |
= |
depth of box section, in metres |
|
9.3 Support structure for machinery on deck
9.3.1 The deck plating and underdeck structure are to be reinforced under
machinery. Acceptable stress levels are as follows:
- σ ≤ 0,75σref
- τ ≤ 0,47σref
- σe ≤ 0,85 σref
Where
|
σ |
= |
normal stress, in N/mm2 |
|
τ |
= |
shear stress, in N/mm2 |
|
σe |
= |
equivalent stress, in N/mm2 |
|
σref |
= |
reference stress of the material, in N/mm2 |
| = |
 |
|
kL |
= |
as defined in Table 2.1.1 Values of k
L
|
9.3.2 Insert plates are to be incorporated in the deck plating in way of machinery
foundations where considered necessary to limit deflection and reduce stress
concentrations. The thickness of the insert plates is to be as required by the
designer’s calculations but in no case is to be taken as less than 1,5 times the
thickness of the adjacent attached plating.
9.3.3 Where fitted, all inserts are to have well radiused corners and be suitably edge
prepared prior to welding. The connection between the insert plate and the adjacent
deck plating is to be full penetration. All other welding in way of the insert plate
is generally to be double continuous and full penetration in way of critical
locations. Tapers are to be not less than three to one.
|