Section
1 General
1.1 Application
1.1.1 This
Chapter applies, in general, to manned or unmanned self-propelled
or non-self-propelled ships defined as follows:
-
Dredgers designed
to operate wholly or generally for the purpose of raising spoil such
as mud, silt, gravel, clay, sand or similar substances, general rubbish
or ore, minerals, etc. for the bed of the sea, rivers, lakes, canals
or harbours, etc. The dredged material may be placed in suitably designed
holds or similar spaces within the ship.
-
Hopper dredgers,
designed to raise spoil, as described in Pt 4, Ch 12, 1.1 Application 1.1.1, and so arranged that the
dredged material may be placed in one or more hoppers within the ship.
For the purpose of this definition, a hopper is a hold or other space
designed to carry dredged spoil and also arranged to enable such spoil
to be discharged through doors or valves in the bottom of the ship.
Spaces arranged to be unloaded by means of conveyor belts, suction
pipes or similar gear are not to be regarded as hoppers unless adequate
bottom doors or valves are also fitted.
-
Split hopper
dredgers, which are designed similarly to that described in Pt 4, Ch 12, 1.1 Application 1.1.1.(b) but arranged such that the
spoil is discharged through the bottom of the ship by means of the
split hull being separated using hinges and actuating devices.
-
Reclamation craft,
reclamation ships, etc. which work in a manner similar to dredgers
but draw their spoil from dredging craft and discharge it ashore.
-
Hopper barges
designed to carry spoil or dredged material in hoppers within the
ship. For the definition of a hopper, see
Pt 4, Ch 12, 1.1 Application 1.1.1.(b).
-
Split hopper
barges, which are designed similarly to that described in Pt 4, Ch 12, 1.1 Application 1.1.1.(e) but arranged such that the
spoil is discharged through the bottom of the ship by means of the
split hull being separated using hinges and actuating devices.
1.1.3 Where
bottom dump doors or valves are fitted, hatch covers are not required.
Proposals for the omission of hatch covers where bottom dump doors
or valves are not fitted will be specially considered.
1.1.4 Ships
which have their machinery placed on a shallow raft, rather than within
a hull, will have their scantlings specially considered. Dredgers
which resemble drilling rigs, or similar offshore structures, in their
design or mode of operation will be considered under the Rules for
such structures.
1.1.5 Ships
of unusual form or proportions, or intended for unusual dredging methods,
will receive individual consideration on the basis of the general
standards of the Rules.
1.1.6 The
requirements provide for transverse and longitudinal framing of the
structure. In general, the midship region scantlings are to extend
over the full length of hoppers and holds. The extent is to be not
less than 0,4L amidships, and may need to be increased
if the design and loading conditions of a particular ship result in
its maximum bending moment occurring other than at amidships.
1.2 Stability
1.2.1 Attention
is drawn to the thixotropic properties of certain types of dredged
material which, as a result of the ship's motions, can cause the spoil
to shift within spoil spaces, resulting in undesirable changes in
trim or angles of heel. This can be particularly dangerous in ships
with closed top spaces.
1.3 Class notations
1.3.1 In
general, ships complying with the requirements of this Chapter will
be eligible for one of the following classes:
-
100A1 dredger. This class will be assigned to ships as defined in Pt 4, Ch 12, 1.1 Application 1.1.1.
-
100A1 hopper
dredger. This class will be assigned to ships as defined in Pt 4, Ch 12, 1.1 Application 1.1.1.(b).
-
100A1 split
hopper dredger. This class will be assigned to ships as defined
in Pt 4, Ch 12, 1.1 Application 1.1.1.(c)
-
100A1 reclamation
craft. This class will be assigned to ships as defined in Pt 4, Ch 12, 1.1 Application 1.1.1.(d).
-
100A1 hopper
barge. This class will be assigned to ships as defined in Pt 4, Ch 12, 1.1 Application 1.1.1.(e).
-
100A1 split
hopper barge. This class will be assigned to ships as defined
in Pt 4, Ch 12, 1.1 Application 1.1.1.(f).
1.3.2 The
class notations will be assigned to ships based on the following:
-
The class notations in Pt 4, Ch 12, 1.3 Class notations 1.3.1 will be assigned to ships which are intended to
make unrestricted sea-going voyages, either as part of their work or while
transferring from one work area to another as part of their normal operations and
have also been designed to perform dredging operations in defined dredging service
areas.
-
Where dredger types listed in Pt 4, Ch 12, 1.3 Class notations 1.3.1.(b), Pt 4, Ch 12, 1.3 Class notations 1.3.1.(c), Pt 4, Ch 12, 1.3 Class notations 1.3.1.(e) and Pt 4, Ch 12, 1.3 Class notations 1.3.1.(f) perform
dredging operations at reduced freeboards, resulting in a dredging draught
(Tm) greater than the summer draught, the class notation will
be extended as follows: ‘dredging draught T
m of … metres in sea states with H
s <... metres’ and will be subject to special requirements
of National Authorities, see
Pt 4, Ch 12, 1.6 Requirements for dredgers operating at reduced freeboards 1.6.1.
-
Where requested,
the assignment of more than one dredging draught may be considered,
i.e. ‘dredging at draught T
m1…’
and ‘dredging at draught T
m2…’
, etc. provided agreement is obtained from the National Authorities
and the applicable requirements of this Chapter are complied with.
1.3.3 Ships
intended to be operated only in suitable areas or conditions which
have been agreed by the Committee, as defined in Pt 1, Ch 2, 2.3 Class notations (hull) 2.3.6, Pt 1, Ch 2, 2.3 Class notations (hull) 2.3.7, Pt 1, Ch 2, 2.3 Class notations (hull) 2.3.8 and Pt 1, Ch 2, 2.3 Class notations (hull) 2.3.10,
will receive individual consideration on the basis of the Rules with
respect to the environmental conditions agreed for the design basis
and approval. In particular, dredgers complying with the requirements
of this Chapter and Pt 3, Ch 13, 7 Equipment for
the reduced equipment requirements, will be eligible to be classed:
-
A1 dredger protected waters service, see
Pt 1, Ch 2, 2.3 Class notations (hull) 2.3.6, or
100A1 dredger with service restriction notation.
whichever is applicable. Hopper dredgers, split hopper dredgers,
reclamation craft, hopper barges and split hopper barges would be
considered similarly.
1.3.4 Where
a ship complying with the requirements of this Chapter has the bottom
structure additionally strengthened for operating aground in accordance
with Pt 4, Ch 12, 7 Bottom strengthening for operating aground, it will be eligible
for the special feature notation `bottom strengthened for operating
aground'.
1.3.5 In
addition to the above notations, an appropriate descriptive note may
be entered in the Register Book indicating the type of
dredging or reclamation craft (see
Pt 1, Ch 2, 2.6 Class notations (refrigerated cargo installations (RMC), controlled atmosphere (CA) systems and carriage
of refrigerated containers (CRC)) 2.6.1), e.g. `trailing
suction dredger', `cutter suction dredger', `bucket dredger', `grab
dredger', `dipper dredger', `self-discharging sand dredger', etc.
1.4 Information required
1.4.1 In
addition to the information and plans required by Pt 3, Ch 1, 5 Information required details of the following
are to be submitted:
- Sections through hoppers, wells, pump-rooms and dredging machinery
spaces.
- Hopper, hold and well bulkheads and associated weirs.
- Scarfing arrangements at hopper, hold and well ends.
- Hinges, actuating and locking arrangements, together with supporting
structure, weld connection details and calculations of design forces
for split hull separation devices.
- Deckhouse and deckhouse support structure.
- Outline arrangement and main scantlings of `A' frames, gantries,
positioning spuds, hopper doors and similar items, the strength and
integrity of which directly affect the hull structure of the vessel.
Support structure in way of `A' frames, positioning spuds and other
dredging structures. Seats of dredging machinery and pumps. If dredging
equipment is stored during voyages, plans of any special arrangements
for dismantling, storage and reassembly. Sufficient particulars of
static and dynamic loading for these items are to accompany the details
to enable verification of the strength and effectiveness of the supporting
ship structure.
- A full set of stability data which is to be placed on board the
ship, see
Pt 1, Ch 2, 3 Surveys - General.
- Calculations of hull girder still water bending moment and shear
force where applicable, see
Pt 4, Ch 12, 2.1 General 2.1.1, for the proposed loading
conditions, including densities of spoil. When the still water bending
moment and block coefficient are being calculated, any water within
spoil spaces should be regarded as added weight, whilst that in dredging
ladder wells and spud wells should be regarded as lost buoyancy.
1.5 Symbols
1.5.1 The
following symbols and definitions are applicable to this Chapter unless
otherwise stated:
|
B
|
= |
breadth,
in metres, defined as the greatest moulded breadth excluding any localised
bulge on the hull associated with the attachment or handling of the
dredging gear |
|
C
b
|
= |
the moulded block coefficient at draught T but
is to be taken as not less than 0,6. The block coefficient is to be
determined using the length, L. Spoil spaces should be
regarded as added weight, whilst dredging ladder wells and spud wells
should be regarded as lost buoyancy
|
|
C
bm
|
= |
the moulded block coefficient at the dredging draught T
m, but is to be taken as not less than 0,6. The block coefficient
is to be determined using length, L. Spoil spaces should
be regarded as added weight, whilst dredging ladder wells and spud
wells should be regarded as lost buoyancy
|
|
D
|
= |
moulded
depth, in metres, to the uppermost continuous deck |
|
L
|
= |
Rule
length, in metres, as defined in Pt 3, Ch 1, 6 Definitions for ships classed for unrestricted service. For ships
classed A1 protected waters service where the load waterline
is not required to be determined by the International Load Line Convention
method, the length is to be measured on the deepest waterline at which
the ship is designed to operate. On sea-going vessels with unusual
stern arrangement, or with unusual bow arrangement associated with
a dredging draught in excess of the summer load line draught, the
length, L, will be specially considered
|
|
M
s
|
= |
design still water bending moment, in kNm, at draught, T, or
less |
|
= |
maximum permissible still water bending moment, in kNm, at draught,
T, or less |
|
M
sm
|
= |
design still water bending moment, in kNm, under dredging conditions
at draught, T
m
|
|
= |
maximum permissible still water bending moment, in kNm, under
dredging conditions at draught, T
m
|
|
T
|
= |
summer
draught, in metres, as established by the method described in the
International Load Line Convention, measured from top of keel amidships |
|
T
m
|
= |
maximum dredging draught, in metres, at which the ship is designed
to operate. It is to be measured amidships from the top of keel and
is to be taken not less than T, see
Pt 4, Ch 12, 15.1 General 15.1.4
|
|
ρ |
= |
relative density
(specific gravity) which, in general, is to be taken not less than
1,86, or as derived from the stowage rate of spoil. This stowage rate
of dredged spoil is to be determined from the maximum spoil weight
at dredging draught and volume of spoil space up to the sill of the
uppermost overflow weir. The value used in the calculations of scantlings
is to be clearly marked on the relevant plans |
Hogging bending moments are positive.
1.6 Requirements for dredgers operating at reduced freeboards
1.6.1 Requirements
of IMO DR 68 Guidelines for the Operation of Dredgers at Reduced
Freeboards are to be complied with.
1.6.2 The
dredger is to be of a self discharging type and equipped with bottom
valves. When the ship is operating at a reduced freeboard, i.e. 1/2
or 1/3 of its summer freeboard, the capacity of these bottom valves,
or a part thereof, is to be sufficient to obtain the summer freeboard
by discharging the appropriate amount of cargo within 8 minutes (IMO
DR 68 refers).
1.6.3 Where
the class notation ‘dredging draft T
m of
… metres in sea states with H
s <…
metres’
is assigned, the Master is to be provided with
suitable information on the actual situation of the sea conditions
and the forecast in terms of significant wave heights.
|