Regulation 9.1
1 This regulation is intended to minimize the impact of flooding from a minor
grounding. Special attention should be paid to the vulnerable area at the turn of the
bilge. When justifying a deviation from fitting an inner bottom, an assessment of the
consequences of allowing a more extensive flooding than reflected in the regulation
should be provided.
2 The determination regarding the requirement to fit a double bottom "as far as this is
practicable and compatible with the design and proper working of the ship" is made, or
should be accepted by, the Administration or a recognized organization acting on its
behalf.
3 Compliance with the damage stability requirement in regulation 9.8 should
not be considered as an equivalent optional requirement to the fitting of a
dimensionally compliant double bottom. This is because a flooded watertight compartment,
such as an engine-room, that complies with the damage stability requirement in
regulation 9.8 is not equivalent to a flooded double bottom below that compartment.
Compliance with the damage stability requirement in regulation 9.8 is intended to
provide a minimum level of safety in cases when the fitting of a double bottom is not
practicable or compatible with the design and proper working of the ship.
Regulation 9.2
1 Except as provided in regulations 9.3 and 9.4, parts of the double bottom not extended
for the full width of the ship as required by regulation 9.2 should be considered an
unusual arrangement for the purpose of this regulation and should be handled in
accordance with regulation 9.7. An example is provided below.
2 If an inner bottom is located higher than the partial subdivision draught
dp, this should be considered an unusual arrangement and is to
be handled in accordance with regulation 9.7.
Regulations 9.3.2.2, 9.6 and 9.7
For cargo ships of less than 80 m in length (L), the alternative arrangements to
provide a level of safety satisfactory to the Administration should be limited to
compartments not having a double bottom, having an unusual bottom arrangement, or having
an "other well" extending below the required double bottom height that is greater than
the h/2 or 500 mm limit indicated in regulation 9.3.2.1. In these cases
compliance with the bottom damage standard in regulation 9.8 should be demonstrated
assuming that the damage will only occur between the transverse watertight bulkheads in
compartments not having a double bottom, having an unusual bottom arrangement, or having
an "other well" extending below the required double bottom height that is greater than
the h/2 or 500 mm limit indicated in regulation 9.3.2.1.
Regulation 9.6
1 Any part of a passenger ship or a cargo ship of 80 m in length (L) and upwards
where a double bottom is omitted in accordance with regulation 9.1, 9.4 or 9.5 shall be
capable of withstanding bottom damages, as specified in regulation 9.8. The intent of
this provision is to specify the circumstances under which the Administration should
require calculations, which damage extents to assume and what survival criteria to apply
when double bottoms are not fitted.
2 The definition of "watertight" in regulation 2.17 implies that the strength of inner
bottoms and other boundaries assumed to be watertight should be verified if they are to
be considered effective in this context.
Regulation 9.7
The reference to a "plane" in regulation 9.2 does not imply that the surface of the inner
bottom may not be stepped in the vertical direction. Minor steps and recesses need not
be considered unusual arrangements for the purpose of this paragraph as long as no part
of the inner bottom is located below the reference plane. Discontinuities in way of wing
tanks are covered by regulation 9.4.
Regulation 9.8
1 For ships to which the probabilistic damage stability requirements of part B-1 apply,
the term "all service conditions" used in this paragraph means the three loading
conditions with all trims used to calculate the attained subdivision index A. For
ships not subject to the probabilistic damage stability requirements in part B-1, such
as cargo ships that comply with the subdivision and damage stability requirements of
other instruments as allowed by regulation II-1/4.2.1.2 and cargo ships of less than 80
m in length (L), "all service conditions" means that the limit curves or tables
required by regulation 5-1.2.1 should include values calculated for the same draught and
trim range(s) as for the other applicable stability requirements.
2 The damage extents specified in this paragraph should be applied to all parts of the
ship where no double bottom is fitted, as permitted by regulations 9.1, 9.4 or 9.5, and
include any adjacent spaces located within the extent of damage. Small wells in
accordance with regulation 9.3.1 do not need to be considered damaged even if within the
extent of the damage. Possible positions of the damages are shown in an example below
(parts of the ship not fitted with a double bottom are shaded; the damages to be assumed
are indicated by boxes).
Regulation 9.9
1 For the purpose of identifying "large lower holds", horizontal surfaces having a
continuous deck area greater than approximately 30% in comparison with the waterplane
area at subdivision draught should be taken to be located anywhere in the affected area
of the ship. For the alternative bottom damage calculation, a vertical extent of
B/10 or 3 m, whichever is less, should be assumed.
2 The increased minimum double bottom height of not more than B/10 or 3 m,
whichever is less, for passenger ships with large lower holds, is applicable to holds in
direct contact with the double bottom. Typical arrangements of ro-ro passenger ships may
include a large lower hold with additional tanks between the double bottom and the lower
hold, as shown in the figure below. In such cases, the vertical position of the double
bottom required to be B/10 or 3 m, whichever is less, should be applied to the
lower hold deck, maintaining the required double bottom height of B/20 or 2 m,
whichever is less (but not less than 760 mm). The figure below shows a typical
arrangement of a modern ro-ro passenger ferry.
