Section
4 Watertight integrity
4.1 Watertight boundaries
4.1.1 All units are to be provided with watertight bulkheads, decks and flats
to give adequate strength and the arrangements are to suit the requirements for
subdivision, floodability and damage stability. In all cases, the plans submitted
are to clearly indicate the location and extent of the bulkheads. In the case of
column-stabilised drilling units, the scantling of the watertight flats and
bulkheads are to be made effective to that point necessary to meet the requirements
of damage stability and are to be indicated on the appropriate plans.
4.2 Tank boundaries
4.2.1 Deep tanks for fresh water, fuel oil or any other tanks which are not
normally kept filled in service are, in general, to have wash bulkheads or
divisions.
4.2.2 Tank bulkheads and watertight divisions are to have adequate strength
for the maximum design pressure head in normal operating and damage conditions and
the scantlings are to comply with Pt 4, Ch 6, 7 Bulkheads.
4.3 Boundary penetrations
4.3.1 Where internal boundaries are required to be watertight to meet damage
stability requirements, the number of openings in such boundaries is to be reduced
to the minimum compatible with the design and proper working of the unit.
4.3.2 Where piping, including air and overflow pipes, ventilation ducts,
shafting, electric cable runs, etc. penetrate watertight boundaries, arrangements
are to be made to ensure the watertight integrity of the boundary. Details of the
arrangements are to be submitted for approval.
4.3.4 Where pipelines or ducts serve more than one compartment, satisfactory
arrangements are to be provided to preclude the possibility of progressive flooding
through the system to other spaces in the event of damage, see also
Pt 4, Ch 7, 3.2 Damage zones.
4.3.5 Where piping systems and ventilation ducts are designed to watertight
standards and are suitable for the maximum design pressure head in damage
conditions, they are to be provided with valves at the boundaries of each watertight
compartment served.
4.3.6 Ventilation ducts which are of non-watertight construction are to be
provided with valves where they penetrate watertight subdivision boundaries.
4.3.7 Where valves are provided at watertight boundaries to maintain
watertight integrity in accordance with Pt 4, Ch 7, 4.3 Boundary penetrations 4.3.5 and Pt 4, Ch 7, 4.3 Boundary penetrations 4.3.6, these valves are to be capable of being operated from a
pump-room or other normally manned space, a weather deck, or a deck which is above
the final waterline after flooding. In the case of a column-stabilised unit, this
would be the central ballast control station. Valve position indicators should be
provided at the remote control station, weather deck or a normally manned space.
4.3.8 For self-elevating units, the ventilation system valves required to
maintain watertight integrity should be kept closed when the unit is afloat.
Necessary ventilation in this case should be arranged by alternative approved
methods.
4.4 Internal openings related to damage
stability
4.4.1 The requirements for the operation, alarm displays and controls of
watertight doors and hatch covers and other closing appliances are given in Pt 7, Ch 1, 9 Riser systems.
4.4.2 Internal access openings fitted with appliances to ensure watertight
integrity, are to comply with the following:
- Watertight doors and hatch covers which are
used during the operation of the unit while afloat may normally be open,
provided the closing appliances are capable of being remotely controlled
from a damage central control room on a deck which is above any final
waterline after flooding and are also to be operable locally from each side
of the bulkhead. Open/shut indicators are to be provided in the control room
showing whether the doors are open or closed. In addition, remotely operated
doors provided to ensure the watertight integrity of internal openings which
are used while at sea are to be sliding watertight doors with audible alarm.
The power, control and indicators are to be operable in the event of main
power failure. Particular attention is to be paid to minimising the effect
of control system failure. Each power-operated sliding watertight door is to
be provided with an individual hand-operated mechanism. It shall be possible
to open/close the door by hand at the door itself from both sides.
- Doors or hatch covers in self-elevating units
or doors placed above the deepest load line draft in column-stabilised and
surface units, which are normally closed while the unit is afloat may be of
the quick acting type and should be provided with an alarm system (e.g.
light signals) showing personnel both locally and at the central ballast
control station whether the doors or hatch covers in question are open or
closed. A notice should be affixed to each such door or hatch cover stating
that it is not to be left open while the unit is afloat.
- The closing appliances are to have strength,
packing and means for securing which are sufficient to maintain
watertightness under the maximum design water pressure head of the
watertight boundary under consideration.
4.4.3 Internal openings fitted with appliances to ensure watertight integrity,
which are to be kept permanently closed while afloat, are to comply with the
following:
- A notice to the effect that the opening is
always to be kept closed while afloat is to be attached to the closing
appliances in question.
- Opening and closing of such closing
appliances are to be noted in the unit’s logbook, or equivalent.
- Manholes fitted with gaskets and closely
bolted covers need not be dealt with as under Pt 4, Ch 7, 4.4 Internal openings related to damage stability 4.4.3.(a).
- The closing appliances are to have strength,
packing and means for securing which are sufficient to maintain
watertightness under the maximum water pressure head of the watertight
boundary under consideration.
4.5 External openings related to damage
stability
4.5.1 Where watertight integrity is dependent on external openings which are
used during the operation of the unit while afloat, they are to comply with the
following:
- The lower edge of openings of air pipes (regardless of their
closing appliances) is to be above the final equilibrium damage waterline
including wind heel effects.
- The lower edge of ventilator openings, doors and hatches with
manually operated means of weathertight closures is to be above the final
equilibrium damage waterline including wind heel effects.
- Openings such as manholes, fitted with
gaskets and closely bolted covers, and side scuttles and windows of the
non-opening type with inside hinged deadlights which are fitted with
appliances to ensure watertight integrity, may be submerged. Such openings
are not allowed to be fitted in the column of stabilised units.
- Scuppers and discharges are to be fitted with closing
appliances, see
Pt 4, Ch 7, 10.1 General.
- Where flooding of chain lockers or other buoyant volumes may
occur, the openings to these spaces should be considered as downflooding
points.
4.6 Strength of watertight doors and hatch
covers
4.6.3 In general, watertight closing appliances are to be designed to withstand
the design pressure head from both sides of the appliance unless the mode of failure
based on the damage stability criteria can only result in one-sided pressure
loading.
4.6.4 The thickness of plating, t, subjected to lateral pressure in
damage conditions is to be not less than:
t = 0,0048s
 mm but not less than 8 mm.
4.6.5 The section modulus, z, of panel stiffeners fitted in one direction and
edge stiffeners is not to be less than:
z = 0,0065s k
 cm3 but not less than 15 cm3
The section modulus of secondary panel stiffeners may also be determined
from the above formula, but doors with stiffeners designed as grillages will be
specially considered.
4.6.6 The moment of inertia, I, of edge stiffeners is in general not to
be less than:
I = 0,8 cm4 (8 cm4)
4.6.8 The strength of the bulkhead and deck framing in way of watertight
closing appliances is to comply with the requirements of Pt 4, Ch 6, 7 Bulkheads.
4.6.10 After installation in the unit, watertight closing appliances are to be
hose tested in accordance with the requirements of Pt 3, Ch 1, 8.3 Trial trip and operational tests 8.3.1 in Pt 3, Ch 1, 8 Inspection and workmanship of the Rules for Ships, and functional tests are to
be carried out to verify the satisfactory operation of the appliance, its control
and alarm functions, as required by Pt 7, Ch 1, 9 Riser systems.
4.7 Weathertight integrity related to
stability
4.7.1 Any opening, such as an air pipe, ventilator, ventilation intake or
outlet, non-watertight sidescuttle, small hatch, door, etc. having its lower edge
submerged below a waterline associated with the zones indicated in (a) or (b), is to
be fitted with a weathertight closing appliance to ensure the weathertight
integrity, when:
- A unit is inclined to the range between the first
intercept of the right moment curve and the wind heeling moment curve and the
angle necessary to comply with the requirements of 2009 MODU Code - Code for the Construction and Equipment of Mobile Offshore Drilling Units, 2009 – Resolution A.1023(26)
during the intact condition of the unit while afloat; and
- A column-stabilised unit is inclined to the
range:
- Necessary to comply with the requirements of Pt 4, Ch 7, 4.7 Weathertight integrity related to stability 4.7.1.(a) and Pt 4, Ch 7, 5.2 Column-stabilised units and tension-leg units 5.2.6 and with a zone measured 4,0 m perpendicularly above
the final damaged waterline per 2009 MODU Code - Code for the Construction and Equipment of Mobile Offshore Drilling Units, 2009 – Resolution A.1023(26) Code referred to Pt 4, Ch 7, 4.7 Weathertight integrity related to stability 4.7.1, and
- Necessary to comply with the requirements of 2009 MODU Code - Code for the Construction and Equipment of Mobile Offshore Drilling Units, 2009 – Resolution A.1023(26).
Figure 7.4.1 Minimum weathertight integrity
requirements for column-stabilised and tension-leg units
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