2.1 General
2.1.1 A craft shall be provided with:
.1 stability characteristics and stabilization systems adequate for safety when the craft is
operated in the non-displacement mode and during the transitional mode;
.2 buoyancy and stability characteristics adequate for safety where the craft is operated
in the displacement mode, both in the intact condition and the damaged condition; and
.3 stability characteristics in the non-displacement and transitional modes adequate to
transfer the craft safely to displacement mode in case of any system malfunction.
2.1.2 Account shall be taken of the effect of icing in the stability calculations. An example of
established practice for ice accretion allowances is given in annex 5 for the guidance of the
Administration.
2.1.3 For the purpose of this and other chapters, unless expressly defined otherwise, the following
definitions apply:
.1 "Downflooding point" means any opening through which flooding of the spaces
which comprise the reserve buoyancy could take place while the craft is in the intact
or damaged condition, and inclines to an angle past the angle of equilibrium.
.2 "Fully submerged foil" means a foil having no lift components piercing the surface of
the water in the foil-borne mode.
.3 "Monohull craft" means any craft which is not a multihull craft.
.4 "Multihull craft" means a craft which in any normally achievable operating trim or
heel angle, has a rigid hull structure which penetrates the surface of the sea over more
than one discrete area.
.5 "Permeability" of a space means the percentage of the volume of that space which can
be occupied by water.
.6 "Skirt" means a downwardly extending, flexible structure used to contain or divide an
air cushion.
2.1.4 Other means of demonstrating compliance with the requirements of any part of this Chapter
may be accepted, provided that the method chosen can be shown to provide an equivalent level of
safety. Such methods may include:
.1 mathematical simulation of dynamic behaviour;
.2 scale model testing; and
.3 full-scale trials.
2.1.5 Model or full-scale tests and/or calculations (as appropriate) shall also include consideration
of the following known stability hazards to which high-speed craft are known to be liable, according
to craft type:
.1 directional instability, which is often coupled to roll and pitch instabilities;
.2 broaching and bow diving in following seas at speeds near to wave speed, applicable
to most types;
.3 bow diving of planing monohulls and catamarans due to dynamic loss of longitudinal
stability in relatively calm seas;
.4 reduction in transverse stability with increasing speed of monohulls;
.5 porpoising of planing monohulls, being coupled pitch and heave oscillations, which
can become violent;
.6 chine tripping, being a phenomenon of planing monohulls occurring when the
immersion of a chine generates a strong capsizing moment;
.7 plough-in of air-cushion vehicles, either longitudinal or transverse, as a result of bow
or side skirt tuck-under or sudden colla pse of skirt geometry, which, in extreme cases,
can result in capsize;
.8 pitch instability of SWATH (small waterplane area twin hull) craft due to the
hydrodynamic moment developed as a result of the water flow over the submerged
lower hulls;
.9 reduction in effective metacentric height (roll stiffness) of surface effect ship (SES) in
high speed turns compared to that on a straight course, which can result in sudden
increases in heel angle and/or coupled roll and pitch oscillations; and
.10 resonant rolling of SES in beam seas, which, in extreme cases, can result in capsize.
2.1.6 Suitable calculations shall be carried out and/or tests conducted to demonstrate that, when
operating within approved operational limitations, the craft will, after a disturbance causing roll,
pitch, heave or heel due to turning or any combination thereof, return to the original attitude.
2.2 Intact buoyancy and watertight and weathertight integrity
2.2.1 Intact buoyancy
2.2.1.1 All craft shall have a sufficient reserve of buoyancy at the design waterline to meet the
intact and damage stability requirements of this chapter. The Administration may require a
larger reserve of buoyancy to permit the craft to operate in any of its intended modes. This
reserve of buoyancy shall be calculated by including only those compartments that are:
.1 watertight and situated below the datum, or
.2 watertight or weathertight and situated above the datum.
In considering the stability after damage, flooding shall be assumed to occur until limited by
watertight boundaries in the equilibrium condition, and weathertight boundaries in intermediate
stages of flooding and within the range of positive righting lever required to satisfy the residual
stability requirements.
Craft built in conformity with the requirements of organizations recognised by the
Administration, in accordance with regulation XI/1 of the Convention may be considered to
possess adequate strength and integrity.
2.2.1.2 Arrangements shall be provided for checking the watertight or weathertight integrity of
those compartments taken into account in 2.2.1.1, and the details incorporated in the Craft
Operating Manual required by 18.2.1.
2.2.2 Openings in watertight divisions
2.2.2.1 The number of openings in watertight bulkheads shall be reduced to the minimum compatible
with the design and proper working of the craft, and all such doors shall be closed prior to departure
of the craft from the berth.
2.2.2.2 Doors in watertight bulkheads may be hinged or sliding. They shall be shown by suitable
testing to be capable of maintaining the watertight integrity of the bulkhead. Such testing shall be
carried out for both sides of the door and shall apply a pressure head 10% greater than that
determined from the minimum permissible height of a downflooding opening. Testing may be carried
out either before or after the door is fitted into the craft but, where shore testing is adopted,
satisfactory installation in the craft shall be verified by inspection and hose testing.
2.2.2.3 Type approval may be accepted in lieu of testing individual doors, provided the approval
process includes pressure testing to a head equal to, or greater, than the required head (refer
to 2.2.2.2).
2.2.2.4 All watertight doors shall be capable of being operated when the craft is inclined up to 15°,
and shall be fitted with means of indication in the operating compartment showing whether they are
open or closed. All such doors shall be capable of being opened and closed locally from each side of
the bulkhead.
2.2.2.5 Watertight doors shall remain closed when the craft is at sea, except that they may be opened
for access. A notice shall be attached to each door to the effect that it is not to be left open.
2.2.2.6 Watertight doors shall be capable of being closed by remote control from the operating
compartment in not less than 20 s and not more than 40 s, and shall be provided with an audible
alarm, distinct from other alarms in the area, which will sound for at least 5 s but no more than 10 s
before the doors begin to move whenever the door is closed remotely by power, and continue
sounding until the door is completely closed. The power, control and indicators shall be operable in
the event of main power failure, as required by regulation II-1/15.7.3 of the Convention. In passenger
areas and areas where the ambient noise exceeds 85 dB(A) the audible alarm shall be supplemented
by an intermittent visual signal at the door. If the Administration is satisfied that such doors are
essential for the safe work of the craft, hinged watertight doors having only local control may be
permitted for areas to which crew only have access, provided they are fitted with remote indicators as
required by 2.2.2.4.
2.2.2.7 Where pipes, scuppers, electric cables, etc. are carried through watertight divisions, the
arrangements for creating a watertight penetration shall be of a type which has been prototype tested
under hydrostatic pressure equal to or greater than that required to be withstood for the actual
location in the craft in which they are to be installed. The test pressure shall be maintained for at
least 30 min and there must be no leakage through the penetration arrangement during this period.
The test pressure head shall be 10% greater than that determined from the minimum permissible
height of a downflooding opening. Watertight bulkhead penetrations which are effected by
continuous welding do not require prototype testing. Valves on scuppers from weathertight
compartments, included in the stability calculations, shall have arrangements for remote closing from
the operating station.
2.2.2.8 Where a ventilation trunk forms part of a watertight boundary, the trunk shall be capable of
withstanding the water pressure that may be present taking into account the maximum inclination
angle allowable during all stages of flooding.
2.2.3 Inner bow doors
2.2.3.1 Where ro-ro craft are fitted with bow loading openings, an inner bow door shall be fitted
abaft such openings, to restrict the extent of flooding in the event of failure of the outer closure. This
inner bow door, where fitted, shall be:
.1 weathertight to the deck above, which deck shall itself be weathertight forward to the
bow loading opening;
.2 so arranged as to preclude the possibility of a bow loading door causing damage to it
in the case of damage to, or detachment of, the bow loading door;
.3 forward of all positions on the vehicle deck in which vehicles are intended to be
carried; and
.4 part of a boundary designed to prevent flooding into the remainder of the craft.
2.2.3.2 A craft shall be exempted from the requirement for such an inner bow door where one of the
following applies:
.1 the vehicle loading deck at the inner bow door position is above the design waterline
by a height more than the significant wave height corresponding to the worst intended
conditions;
.2 it can be demonstrated using model tests or mathematical simulations that when the
craft is proceeding at a range of speeds up to the maximum attainable speed in the
loaded condition at all headings in long crested seas of the greatest significant wave
height corresponding to the worst intended conditions, either:
.1 the bow loading door is not reached by waves; or
.2 having been tested with the bow loading door open to determine the
maximum steady state volume of water which accumulates, it can be shown
by static analysis that, with the same volume of water on the vehicle deck(s)
the residual stability requirements of 2.6.11 and 2.13 or 2.15 are satisfied. If
the model tests or mathematical simulations are unable to show that the
volume of water accumulated reaches a steady state, the craft shall be
considered not to have satisfied the conditions of this exemption.
Where mathematical simulations are employed they shall already have been verified
against full-scale or model testing;
.3 bow loading openings lead to open ro-ro spaces provided with guard-rails or having
freeing ports complying with 2.2.3.2.4;
.4 the deck of the lowest ro-ro space above the design waterline is fitted on each side of
the deck with freeing ports evenly distributed along the sides of the compartment.
These shall either be proven to be acceptable using tests according to 2.2.3.2.2 above
or comply with the following:
.1 A > 0.3 l
where :
A = the total area of freeing ports on each side of the deck in m2;
and
l = the length of the compartment in m;
.2 the craft shall maintain a residual freeboard to the deck of the ro-ro space of at
least 1 m in the worst condition;
.3 such freeing ports shall be located within the height of 0.6 m above the deck
of the ro-ro space, and the lower edge of the ports shall be within 0.02 m
above the deck of the ro-ro space; and
.4 such freeing ports shall be fitted with closing devices or flaps to prevent water
entering the deck of the ro-ro space whilst allowing water which may
accumulate on the deck of the ro-ro space to drain.
2.2.4 Other provisions for ro-ro craft
2.2.4.1 All accesses in the ro-ro space that lead to spaces below the deck shall have a lowest point
which is not less than the height required from the tests conducted according to 2.2.3.2.2 or 3 m
above the design waterline.
2.2.4.2 Where vehicle ramps are installed to give access to spaces below the deck of the ro-ro space,
their openings shall be capable of being closed weathertight to prevent ingress of water below.
2.2.4.3 Accesses in the ro-ro space that lead to spaces below the ro-ro deck and having a lowest point
which is less than the height required from the tests conducted according to 2.2.3.2.2 or 3 m above
the design waterline may be permitted provided they are watertight and are closed before the craft
leaves the berth on any voyage and remain closed until the craft is at its next berth.
2.2.4.4 The accesses referred to in 2.2.4.2 and 2.2.4.3 above shall be fitted with alarm indicators in
the operating compartment.
2.2.4.5 Special category spaces and ro-ro spaces shall be patrolled or monitored by effective means,
such as television surveillance, so that any movement of vehicles in adverse weather conditions and
unauthorised access by passengers thereto can be detected whilst the craft is underway (refer
to 7.8.3.1).
2.2.5 Indicators and surveillance
2.2.5.1 Indicators
Indicators shall be provided in the operating compartment for all shell doors, loading doors and other
closing appliances which, if left open or not properly secured, could lead to major flooding in the
intact and damage conditions. The indicator system shall be designed on the fail-safe principle and
shall show by visual alarms if the door is not fully closed or if any of the securing arrangements are
not in place and fully locked, and by audible alarms if such door or closing appliance becomes open
or the securing arrangements become unsecured. The indicator panel in the operating compartment
shall be equipped with a mode selection function 'harbour/sea voyage' so arranged that an audible
alarm is given in the operating compartment if the craft leaves harbour with the bow doors, inner
doors, stern ramp or any other side shell doors not closed or any closing device not in the correct
position. The power supply for the indicator systems shall be independent of the power supply for
operating and securing the doors.
2.2.5.2 Television surveillance
Television surveillance and a water leakage detection system shall be arranged to provide an
indication to the operating compartment and to the engine control station of any leakage through
inner and outer bow doors, stern doors or any other shell doors which could lead to major flooding.
2.2.6 Integrity of superstructure
2.2.6.1 Where entry of water into structures above the datum would significantly influence the
stability and buoyancy of the craft, such structures shall be:
.1 of adequate strength to maintain the weathertight integrity and fitted with
weathertight closing appliances; or
.2 provided with adequate drainage arrangements; or
.3 an equivalent combination of both measures.
2.2.6.2 Weathertight superstructures and deckhouses located above the datum shall in the outside
boundaries have means of closing openings with sufficient strength such as to maintain weathertight
integrity in all damage conditions where the space in question is not damaged. Furthermore, the
means of closing shall be such as to maintain weathertight integrity in all operational conditions.
2.2.7 Doors, windows, etc., in boundaries of weathertight spaces
2.2.7.1 Doors, windows, etc., and any associated frames and mullions in weathertight superstructures
and deckhouses shall be weathertight and shall not leak or fail at a uniformly applied pressure less
than that at which adjacent structure would experience permanent set or fail. Conformity with the
requirements of organizations recognized by the Administration in accordance with regulation XI/1
of the Convention may be considered to possess adequate strength.
2.2.7.2 For doors in weathertight superstructures, hose tests shall be carried out with a water pressure
from the outside in accordance with specifications at least equivalent to those acceptable to the
Organization*.
2.2.7.3 The height above the deck of sills to doorways leading to exposed decks shall be as high
above the deck as is reasonable and practicable, particularly those located in exposed positions. Such
sill heights shall in general not be less than 100 mm for doors to weathertight spaces on decks above
the datum, and 250 mm elsewhere. For craft of 30 m in length and under, sill heights may be reduced
to the maximum which is consistent with the safe working of the craft.
2.2.7.4 Windows shall not be permitted in the boundaries of special category spaces or ro-ro spaces
or below the datum. If required by restrictions in the Permit to Operate, forward facing windows, or
windows which may be submerged at any stage of flooding shall be fitted with hinged or sliding
storm shutters ready for immediate use.
2.2.7.5 Side scuttles to spaces below the datum shall be fitted with efficient hinged deadlights
arranged inside so that they can be effectively closed and secured watertight.
2.2.7.6 No side scuttle shall be fitted in a position so that its sill is below a line drawn parallel to and
one metre above the design waterline.
2.2.8 Hatchways and other openings
2.2.8.1 Hatchways closed by weathertight covers
The construction and the means for securing the weathertightness of cargo and other hatchways shall
comply with the following:
.1 coaming heights shall in general not be less than 100 mm for hatches to weathertight
spaces on decks above the datum, and 250 mm elsewhere. For craft of 30 m in length
and under, coaming heights may be reduced to the maximum which is consistent with
the safe working of the craft;
.2 the height of these coamings may be reduced, or the coamings omitted entirely, on
condition that the Administration is satisfied that the safety of the ship is not thereby
impaired in any sea conditions up to the worst intended conditions. Where coamings
are provided, they shall be of substantial construction; and
.3 the arrangements for securing and maintaining weathertightness shall ensure that the
tightness can be maintained in any sea conditions up to the worst intended conditions.
* Refer to ISO 6042 - Ships and Marine Technology - Weathertight single-leaf steel doors, or a similar
standard.