Section
13 Hatch coamings
13.1 General
13.1.1 The
height and construction of forward and side hatch coamings are to
comply with the following requirements. All hatch coamings are to
comply with the requirements of Pt 3, Ch 11, 5.1 General 5.1.1, Pt 3, Ch 11, 5.1 General 5.1.4, Pt 3, Ch 11, 5.2 Construction 5.2.1, Pt 3, Ch 11, 5.2 Construction 5.2.2, Pt 3, Ch 11, 5.2 Construction 5.2.4 to Pt 3, Ch 11, 5.2 Construction 5.2.12, Pt 3, Ch 11, 5.2 Construction 5.2.16 to Pt 3, Ch 11, 5.2 Construction 5.2.18 and Pt 3, Ch 11, 5.4 Rest bars in hatchways 5.4.1.
13.1.2 For
the structure of hatch coamings and coaming stays, the corrosion addition t
c is to be 1,5 mm.
13.1.3 Material
for the hatch coamings is to be steel according to the requirements
for the ship’s hull.
13.1.4 The
secondary stiffeners of the hatch coamings are to be continuous over
the breadth and length of the hatch coamings.
13.2 Load model
13.2.1 The
pressure p
coam, on hatch coamings is to be
taken as 220 kN/m2.
13.3 Local net plate thickness
13.3.1 The
local net plate thickness, t, in mm, of the hatch coaming
plating is to be the greater of 9,5 mm or the following:
where
|
s
|
= |
secondary
stiffener spacing, in metres |
|
P
coam
|
= |
pressure, in kN/m2, as defined in Pt 4, Ch 7, 13.2 Load model 13.2.1
|
|
S
coam
|
= |
safety factor to be taken equal to 1,15 |
|
σa,coam
|
= |
0,95σF.
|
|
σF
|
= |
minimum
upper yield stress, in N/mm2, of the material.
|
13.4 Net scantlings of longitudinal and transverse secondary stiffeners
13.4.1 The
required section modulus, Z, in cm3, of the
longitudinal or transverse secondary stiffeners of the hatch coamings,
based on net member thickness, is given by:
where
|
m
|
= |
16
in general |
|
|
= |
12 for the end
spans of stiffeners sniped at the coaming corners |
|
S
coam
|
= |
safety factor to be taken equal to 1,15 |
|
l |
= |
span of
secondary stiffeners, in metres |
|
s
|
= |
spacing
of secondary stiffeners, in metres |
|
p
coam
|
= |
pressure in kN/m2 as defined in Pt 4, Ch 7, 13.2 Load model 13.2.1
|
|
c
p
|
= |
ratio of the plastic section modulus to the elastic section
modulus of the secondary stiffeners with an attached plate breadth
equal to 40t, where t is the plate net thickness,
in mm
|
|
|
= |
1,16 in the absence
of more precise evaluation |
|
σa,coam
|
= |
0,95σF
|
|
σF
|
= |
minimum
upper yield stress, in N/mm2, of the material.
|
13.5 Net scantlings of coaming stays
13.5.1 The
required minimum section modulus, Z, in cm3,
and web thickness, t
w, in mm of coaming stays
designed as beams with flange connected to the deck or sniped and
fitted with a bracket (see
Figure 7.13.1 Typical coaming stays, Type A and B) at their connection with the deck,
based on member net thickness, are given by:
where
|
H
C
|
= |
stay height, in metres |
|
s
|
= |
stay
spacing, in metres |
|
h
|
= |
stay
depth at the connection with the deck, in mm |
|
p
coam
|
= |
pressure, in kN/m2, as defined in Pt 4, Ch 7, 13.2 Load model 13.2.1
|
|
σ
a,coam
|
= |
0,95σF
|
|
t
a,coam
|
= |
0,5σF
|
|
σF
|
= |
minimum
upper yield stress, in N/mm2, of the material.
|
Figure 7.13.1 Typical coaming stays
13.5.2 For
calculating the section modulus of coaming stays, their face plate
area is to be taken into account only when it is welded with full
penetration welds to the deck plating and adequate underdeck structure
is fitted to support the stresses transmitted by it.
13.5.3 For
other designs of coaming stays, such as those shown in Figure 7.13.1 Typical coaming stays Type C and D, the stress
levels in 12.5 apply and are to be checked at the highest stressed
locations.
13.6 Local details
13.6.1 The
design of local details is to comply with Pt 3, Ch 11, 5 Hatch coamings for the purpose of transferring the pressures on
the hatch covers to the hatch coamings and, through them, to the deck
structures below. Hatch coamings and supporting structures are to
be adequately stiffened to accommodate the loading from hatch covers,
in longitudinal, transverse and vertical directions.
13.6.3 Double
continuous welding is to be adopted for the connections of stay webs
with deck plating and the weld throat is to be not less than 0,44t
W, where t
W is the gross thickness of
the stay web.
13.6.4 Toes
of stay webs are to be connected to the deck plating with deep penetration
double bevel welds extending over a distance not less than 15 per
cent of the stay width.
|