Section
3 Bow doors
3.1 Application
3.1.1 The
requirements of this Section are applicable to the arrangement, strength
and securing of bow doors, both the visor and the side opening type
doors, and inner doors leading to a complete or long forward enclosed
superstructure, or to a long non-enclosed superstructure which is
fitted to attain minimum bow height equivalence.
3.1.2 Other
types of bow door will be specially considered.
3.1.3 Where
the operational requirements dictate that the doors and ramps be deployed
at sea or in the surf zone, the strength and operation will be specially
considered.
3.2 General
3.2.1 The
attention of Owners and Builders is drawn to the additional statutory
regulations for bow doors that may be required by the subdivision
and stability standard.
3.2.2 Bow
doors are to be located above the vertical limit of watertight integrity.
A watertight recess is normally permitted below the vertical limit
of watertight integrity located forward of the collision bulkhead
and above the deepest waterline, for the arrangement of ramps or other
related mechanical devices. For any ship where bow doors may be open
at sea or located below the vertical limit of watertight integrity,
the enclosed spaces protected by the door or ramp are to be considered
open as well as closed in damage stability or flooding conditions.
3.2.3 An inner
door is to be fitted which is to be gasketed and weathertight. The
inner door is to be part of the collision bulkhead. The inner door
need not be fitted directly above the bulkhead below, provided it
is located within the limits specified for the position of the collision
bulkhead, see
Vol 1, Pt 3, Ch 2, 4 Bulkhead arrangements.
A vehicle ramp may be arranged for this purpose, provided its position
complies with Vol 1, Pt 3, Ch 2, 4 Bulkhead arrangements and
the ramp is weathertight over its complete length. In this case the
upper part of the ramp higher than 2,3 m above the vertical limit
of watertight integrity may extend forward of the limit specified
in Vol 1, Pt 3, Ch 2, 4 Bulkhead arrangements If this is not
possible a separate inner weathertight door is to be installed, as
far as practicable within the limits specified for the position of
the collision bulkhead.
3.2.4 Bow
doors are to be fitted as to ensure tightness consistent with operational
conditions and to give effective protection to inner doors. Inner
doors forming part of the collision bulkhead are to be weathertight
over the full height of the vehicle space and arranged with fixed
sealing supports on the aft side of the doors.
3.2.5 Bow
doors and inner doors are to be arranged so as to preclude the possibility
of the bow door causing structural damage to the inner door or to
the collision bulkhead in the case of damage to or detachment of the
bow door. If this is not possible, a separate inner weathertight door
is to be installed, as indicated in Vol 1, Pt 4, Ch 3, 3.2 General 3.2.3.
3.2.6 The
requirements for inner doors are based on the assumption that vehicles
are effectively lashed and secured against movement in the stowed
position.
3.3 Symbols and definitions
3.3.1 The
symbols used in this Section are defined as follows:
|
A
s
|
= |
area stiffener web, in cm2
|
|
A
x
|
= |
area, in m2, of the transverse vertical projection
of the bow door, between the bottom of the door and the top of the
door or between the bottom of the door and the upper deck bulwark,
or between the bottom of the door and the top of the door, including
the bulwark, where it is part of the door, whichever is the lesser, see
Figure 3.3.2 Bow visor upward hinging. Where
the flare angle of the bulwark is at least 15 degrees less than the
flare angle of the adjacent shell plating, the height from the bottom
of the door may be measured to the upper deck or to the top of the
door, whichever is lesser. In determining the height from the bottom
of the door to the upper deck or to the top of the door, the bulwark
is to be excluded.
|
|
A
y
|
= |
area, in m2, of the longitudinal vertical projection
of the bow door, between the bottom of the door and the top of the
upper deck bulwark, or between the bottom of the door and the top
of the door, including the bulwark, where it is part of the door,
whichever is the lesser, see
Figure 3.3.2 Bow visor upward hinging. Where the flare angle
of the bulwark is at least 15 degrees less than the flare angle of
the adjacent shell plating, the height from the bottom of the door
may be measured to the upper deck or to the top of the door, whichever
is the lesser.
|
|
A
z
|
= |
area, in m2, of the horizontal projection of the
bow door, between the bottom of the door and the top of the upper
deck bulwark, or between the bottom of the door and the top of the
door, including the bulwark, where it is part of the door, whichever
is the lesser, see
Figure 3.3.2 Bow visor upward hinging. Where the flare angle of the bulwark is at least 15
degrees less than the flare angle of the adjacent shell plating, the
height from the bottom of the door may be measured to the upper deck
or to the top of the door, whichever is the lesser.
|
|
h
|
= |
height
of the door between the levels of the bottom of the door and the upper
deck or between the bottom of the door and the top of the door, in
metres, whichever is the lesser, as shown in Figure 3.3.1 Definition of αf and βe
|
|
W
bv
|
= |
mass of the visor door, in tonnes |
|
τ |
= |
shear stress,
in N/mm2
|
|
σ |
= |
bending stress,
in N/mm2
|
|
σo
|
= |
specified
minimum yield strength of the material, in N/mm2
|
|
σeq
|
= |
equivalent
stress, in N/mm2
|
| = |
|
3.3.2
Locking
device. A device that locks a securing device in the closed
position.
3.3.3
Securing
device. A device used to keep the door closed by preventing
it from rotating about its hinges.
3.3.4
Side-opening
doors. Side-opening doors are opened either by rotating outwards
about a vertical axis through two or more hinges located near the
outboard edges or by horizontal translation by means of linking arms
arranged with pivoted attachments to the door and the craft. It is
anticipated that side-opening doors are arranged in pairs.
3.3.5
Supporting
device. A device used to transmit external or internal loads
from the door to a securing device and from the securing device to
the ship’s structure, or a device other than a securing device,
such as a hinge, stopper or other fixed device, that transmits loads
from the door to the ship’s structure.
3.3.6
Visor
doors. Visor doors are opened by rotating upwards and outwards
about a horizontal axis through two or more hinges located near the
top of the door and connected to the primary structure of the door
by longitudinally arranged lifting arms.
3.4 Construction and testing
3.4.1 Plans
are to be of sufficient detail for plan approval purposes. Plans showing
the proposed scantlings and arrangement of the bow door are to be
submitted. Bow doors are to be constructed under survey.
3.4.2 Bow
doors fitted below the limit of watertight integrity are to be subject
to a pressure test of a prototype to confirm the design pressure head.
3.5 Strength criteria
3.5.1 Scantlings
of the primary members, securing and supporting devices of bow doors
and inner doors are to be able to withstand the design loads defined
in Vol 1, Pt 4, Ch 3, 3.6 Design loads. The shear, bending and
equivalent stresses are not to exceed 80/k N/mm2,
120/k N/mm2 and 150/k
s N/mm2 respectively.
3.5.2 The
buckling strength of primary members is to be verified as being adequate, see
Vol 1, Pt 6, Ch 2, 3 Buckling
Figure 3.3.1 Definition of αf and βe
Figure 3.3.2 Bow visor upward hinging
3.5.3 For
steel to steel bearings in securing and supporting devices, the nominal
bearing pressure calculated by dividing the design force by the projected
bearing area is not to exceed 80 per cent of the yield stress of the
bearing material. For other bearing materials, the permissible bearing
pressure is to be determined according to the manufacturer’s
specification.
3.5.4 The
arrangement of securing and supporting devices is to be such that
threaded bolts do not carry support forces. The maximum tension in
way of threads of steel bolts not carrying support forces is not to
exceed 125/k N/mm2.
3.6 Design loads
3.6.1 The
design external pressure, P
e, for the determination
of scantlings for primary members, securing and supporting devices
of bow doors is to be taken not less than the following:
|
|
= |
1,0 for sea-going
ships |
|
|
= |
0,8 for ships operated
in coastal waters |
|
|
= |
0,5 for ships operated
in sheltered waters |
|
C
H
|
= |
0,0125L
R for L
R <
80 m
|
|
αf
|
= |
flare
angle, in degrees, at the point to be considered, defined as the angle
between a vertical line and the tangent to the side shell plating,
measured in a vertical plane normal to the horizontal tangent to the
shell plating, see
Figure 3.3.1 Definition of αf and βe
|
|
βe
|
= |
entry
angle, in degrees, at the point to be considered, defined as the angle
between a longitudinal line parallel to the centreline and the tangent
to the shell plating in a horizontal plane, see
Figure 3.3.1 Definition of αf and βe.
|
3.6.2 The
design external forces, F
x, Fy and
Fz, in kN, for the determination of scantlings of securing
and supporting devices of bow doors are taken to be not less than P
e
A
x, P
e
A
y and P
e
A
z respectively.
Where P
e is the external pressure, defined
in Vol 1, Pt 4, Ch 3, 3.6 Design loads 3.6.1, with the flare angle, αf, and the entry angle, βe, measured at the point
on the bow door, ld/2 aft of the stem line on the plane h/2 above the bottom of the door, as shown in Figure 3.3.1 Definition of αf and βe. A
x, A
y, A
z and h as
defined in Vol 1, Pt 4, Ch 3, 3.3 Symbols and definitions 3.3.1
3.6.3 For
bow doors, including bulwark, of unusual form or proportions, the
areas used for the determination of the design values of external
forces will be specially considered.
3.6.4 For
visor doors the closing moment, My, under external loads,
is to be taken as:
|
M
y
|
= |
F
x
a
bv + 10W
bv
c
bv – F
z
b
bv kNm
|
where
W
bv, a
bv, b
bv and c
bv as
defined in Vol 1, Pt 4, Ch 3, 3.3 Symbols and definitions 3.3.1, F
x and F
z as defined in Vol 1, Pt 4, Ch 3, 3.6 Design loads 3.6.2.
3.6.5 The
lifting arms of a visor and its supports are to be dimensioned for
the static and dynamic forces applied during the lifting and lowering
operations, and a minimum wind pressure of 1,5 kN/m2 is
to be taken.
3.6.6 The
design external pressure, in kN/m2, for the determination
of scantlings for primary members, securing and supporting devices
and surrounding structure of inner doors is to be taken as the greater
of 0,45L
R and 10h
2,
where h
2 is the distance, in m, from the load
point to the top of the space enclosed by the visor, L
R, as defined in Vol 1, Pt 3, Ch 1, 5.2 Principal particulars 5.2.2
3.6.7 The
design internal pressure for the determination of scantlings for securing
devices of inner doors is not to be taken less than 25 kN/m2.
3.6.8 On ships
with rounded nose bow and a large stem angle with the waterline, strengthening
against horizontal impact loads is to be considered. Similarly, in
ships with a flare angle of less than 60o with the waterline,
strengthening against vertical impact loads to be considered.
3.7 Scantlings of bow doors
3.7.1 The
strength of bow doors is to be equivalent to the surrounding structure.
3.7.2 Bow
doors are to be adequately stiffened and means are to be provided
to prevent lateral or vertical movement of the doors when closed.
For visor doors adequate strength for the opening and closing operations
is to be provided in the connections of the lifting arms to the door
structure and to the craft structure.
3.7.3 The
thickness of the bow plating is not to be less than that required
for the side shell plating, using bow door stiffener spacing, but
in no case less than the minimum required thickness of fore end shell
plating.
3.7.4 The
section modulus of horizontal or vertical stiffeners is not to be
less than that required for end framing. Consideration is to be given,
where necessary, to differences in fixity between ship's frames and
bow doors stiffeners.
3.7.6 The
bow door secondary stiffeners are to be supported by primary members
constituting the main stiffening of the door.
3.7.7 The
primary members of the bow door and the hull structure in way are
to have sufficient stiffness to ensure integrity of the boundary support
of the door.
3.7.9 The
webs of primary members are to be adequately stiffened, preferably
in a direction perpendicular to the shell plating.
3.8 Scantlings of inner doors
3.8.2 Where
inner doors also serve as vehicle ramps, the scantlings are not to
be less than those required for vehicle decks.
3.8.3 The
distribution of forces acting on the securing and supporting devices
is, in general, to be supported by direct calculations taking into
account the flexibility of the structure and actual position and stiffness
of the supports.
3.9 Securing and supporting of bow doors
3.9.1 Bow
doors are to be fitted with adequate means of securing and supporting
so as to be commensurate with the strength and stiffness of the surrounding
structure. The hull supporting structure in way of the bow doors is
to be suitable for the same design loads and design stresses as the
securing and supporting devices. Where packing is required, the packing
material is to be of a comparatively soft type, and the supporting
forces are to be carried by the steel structure only. Other types
of packing may be considered. Maximum design clearance between securing
and supporting devices is, in general, not to exceed 3 mm. A means
is to be provided for mechanically fixing the door in the open position.
3.9.2 Only
the active supporting and securing devices having an effective stiffness
in the relevant direction are to be included and considered to calculate
the reaction forces acting on the devices. Small and/or flexible devices
such as cleats intended to provide load compression of the packing
material are, in general, not to be included in the calculations called
for in Vol 1, Pt 4, Ch 3, 3.9 Securing and supporting of bow doors 3.9.8. The number of
securing and supporting devices are, in general, to be the minimum
practical whilst taking into account the requirements for redundant
provision given in Vol 1, Pt 4, Ch 3, 3.9 Securing and supporting of bow doors 3.9.9 and Vol 1, Pt 4, Ch 3, 3.9 Securing and supporting of bow doors 3.9.10 and the available space
for adequate support in the hull structure.
3.9.3 For
opening outwards visor doors, the pivot arrangement is generally to
be such that the visor is self closing under external loads, that
is M
y > 0. Moreover, the closing moment, M
y, as given in Vol 1, Pt 4, Ch 3, 3.6 Design loads 3.6.4,
is to be not less than:
|
M
y
|
= |
10W
bv
c
bv +
0,1( +  )0,5 ( +  )0,5
|
where W
bv, a
bv, b
bv and c
bv as
defined in Vol 1, Pt 4, Ch 3, 3.3 Symbols and definitions 3.3.1, F
x and F
z as defined in Vol 1, Pt 4, Ch 3, 3.6 Design loads 3.6.2
3.9.5 For
visor doors the reaction forces applied on the effective securing
and supporting devices assuming the door as a rigid body are determined
for the following combination of external loads acting simultaneously
together with the self weight of the door.
| Case 1
|
F
x and F
z
|
| Case 2
|
0,7F
y acting on each side separately together with 0,7F
x and 0,7F
z.
|
where F
x, F
y and F
z are to be determined as indicated
in Vol 1, Pt 4, Ch 3, 3.6 Design loads 3.6.2 and applied at the
centroid of projected areas.
3.9.6 For
side-opening doors the reaction forces applied on the effective securing
and supporting devices assuming the door as a rigid body are determined
for the following combination of external loads acting simultaneously
together with the self weight of the door:
| Case
1
|
F
x, F
y and F
z acting on both doors.
|
| Case
2
|
0,7F
x and 0,7F
z acting on both doors and 0,7F
y acting on each door separately.
|
where F
x, F
y and F
z are to be determined as indicated
in Vol 1, Pt 4, Ch 3, 3.6 Design loads 3.6.2 and applied at the
centroid of projected areas.
3.9.8 The
distribution of the reaction forces acting on the securing and supporting
devices may require to be supported by direct calculations taking
into account the flexibility of the hull structure and the actual
position and stiffness of the supports.
3.9.9 The
arrangement of securing and supporting devices in way of these securing
devices is to be designed with redundancy so that in the event of
failure of any single securing or supporting device the remaining
devices are capable to withstand the reaction forces without exceeding
by more than 20 per cent the permissible stresses as given in Vol 1, Pt 4, Ch 3, 3.5 Strength criteria 3.5.1.
3.9.10 For
visor doors, two securing devices are to be provided at the lower
part of the door, each capable of providing the full reaction force
required to prevent opening of the door within the permissible stresses
given in Vol 1, Pt 4, Ch 3, 3.5 Strength criteria 3.5.1. The opening
moment, M
o, to be balanced by this reaction
force, is not to be taken less than:
|
M
o
|
= |
10W
bv
d
bv +
5A
x
a
bv kNm
|
where
W
bv, A
x, d
bv and a
bv as
defined in Vol 1, Pt 4, Ch 3, 3.3 Symbols and definitions 3.3.1.
3.9.11 For
visor doors, the securing and supporting devices excluding the hinges
should be capable of resisting the vertical design force (F
z – 10W
bv), in kN, within the
permissible stresses given in Vol 1, Pt 4, Ch 3, 3.5 Strength criteria 3.5.1.
3.9.12 All
load transmitting elements in the design load path, from door through
securing and supporting devices into the ship structure, including
welded connections, are to be the same strength. These elements include
pins, supporting brackets and back-up brackets. Where cut-outs are
made in the supporting structure, the strength and stiffness will
be specially considered.
3.9.13 For
side-opening doors, thrust bearings have to be provided in way of
girder ends at the closing of the two leaves to prevent one leaf to
shift towards the other one under effect of unsymmetrical pressure, see
Figure 3.3.3 Typical thrust bearing. Each
part of the thrust bearing has to be kept secured on the other part
by means of securing devices. Any other arrangement serving the same
purpose is to be submitted for appraisal.
Figure 3.3.3 Typical thrust bearing
3.9.14 The
spacing for side and top cleats should not exceed 2,5 m and there
should be cleats positioned as close to the corners as practicable.
Alternative arrangements for ensuring weathertight sealing will be
specially considered.
3.10 Securing and locking arrangements
3.10.1 Securing
devices are to be simple to operate and easily accessible. Securing
devices are to be equipped with mechanical locking arrangement (self
locking or separate arrangement), or be of the gravity type. The opening
and closing systems as well as securing and locking devices are to
be interlocked in such a way that they can only operate in the proper
sequence.
3.10.2 Bow
doors and inner doors giving access to vehicle decks are to be provided
with an arrangement for remote control, from a position above the
vertical limit of watertight integrity, of:
-
the closing and
opening of the doors, and
-
associated securing
and locking devices for every door.
Indication of the open/closed position of every door and every
securing and locking device is to be provided at the remote control
stations. The operating panels for operation of doors are to be inaccessible
to unauthorised persons. A notice plate, giving instructions to the
effect that all securing devices are to be closed and locked before
leaving harbour, is to be placed at each operating panel and is to
be supplemented by warning indicator lights.
3.10.3 Where
hydraulic securing devices are applied, the system is to be mechanically
lockable in closed position so that in the event of loss of the hydraulic
fluid, the securing devices remain locked. The hydraulic system for
securing and locking devices is to be isolated from other hydraulic
circuits when in closed position.
3.10.4 Separate
indicator lights and audible alarms are to be provided on the navigation
bridge and on the operating panel to show that the bow door and inner
door are closed and that their securing and locking devices are properly
positioned. The indication panel is to be provided with a lamp test
function. The indicator lights are to be provided with a permanent
power supply, further, arrangements are to be such that it is not
possible to turn off these lights in service.
3.10.5 The
indicator system is to be designed on the failsafe principle and is
to show by visual alarms if the door is not fully closed and not fully
locked and by audible alarms if securing devices become open or locking
devices become unsecured. The power supply for the indicator system
is to be independent of the power supply for operating and closing
the doors. The sensors of the indicator system are to be protected
from water, ice formation and mechanical damages.
3.10.6 The
indication panel on the navigation bridge is to be equipped with a
mode selection function ‘harbour/sea voyage’, so arranged
that audible alarm is given if the ship leaves harbour with the bow
door or inner door not closed and with any of the securing devices
not in the correct position.
3.10.7 A
water leakage detection system with audible alarm and television surveillance
are to be arranged to provide an indication to the navigation bridge
and to the engine control room of leakage through the inner door.
3.10.8 Between
the bow door and the inner door a television surveillance system is
to be fitted with a monitor on the navigation bridge and in the machinery
control room. The system is to be able to monitor the position of
doors and a sufficient number of their securing devices. Special consideration
is to be given for lighting and contrasting colour of objects under
surveillance.
3.10.9 A
drainage system is to be arranged in the area between bow door and
ramp, or where no ramp is fitted, between the bow door and inner door.
The system is to be equipped with an audible and visual alarm function
to the navigation bridge being set off when the water levels in these
areas exceed 0,5 m or the high water level alarm, whichever is the
lesser. If not discharged by a bilge suction, scuppers are to be provided
port and starboard having a diameter of not less than 50 mm. Valves
are to be fitted.
3.10.11 Air
pipes from cofferdams or void spaces may terminate in the enclosed
‘tween deck space on the main vehicle deck provided the space
is adequately ventilated and the air pipes are provided with weathertight
closing appliances.
3.11 Operating and Maintenance Manual
3.11.1 An
Operating and Maintenance Manual for the bow door and inner door is
to be provided on board. The manual is to contain the following information:
-
main particulars
and design drawings,
- special safety precautions;
- details of vessel, class and statutory certificates;
- equipment and design loading for ramps;
- key plan of equipment for doors and ramps;
- manufacturers' recommended testing for equipment; and
- a description of the following equipment: bow doors; inner bow
doors; bow/ramp doors; central power pack; bridge panel; ramps leading
down from the main deck; engine control room panel.
-
service conditions:
- limiting heel and trim of the ship for loading/unloading;
- limiting heel and trim for door operations;
- operating instructions for doors and ramps; and
- emergency operating instructions for doors and ramps.
-
maintenance:
- schedule and extent of maintenance;
- troubleshooting and acceptable clearances; and
- manufacturers' maintenance procedures.
-
register of
inspections, including inspection of locking, securing and supporting
devices, repairs and renewals.
This Manual is to be submitted for approval and is to contain
a note recommending that recorded inspections of the door supporting
and securing devices carried out by the ship’s staff at monthly
intervals or following incidents that could result in damage, including
heavy weather or contact in the region of the doors. Any damages recorded
during such inspections are to be reported to LR.
3.11.2 Documented
operating procedures for closing and securing the bow door and inner
door are to be kept on board and posted at an appropriate place.
|