Regulation 27 - Types of ships
(1) For the purposes of freeboard computation,
ships shall be divided into type 'A' and type ’B’.
Type 'A' ships
(2) A type ’A’ ship is one which:
-
(a) is designed to carry only liquid cargoes in
bulk;
-
(b) has a high integrity of the exposed deck with
only small access openings to cargo compartments, closed by watertight
gasketed covers of steel or equivalent material; and
-
(c) has low permeability of loaded cargo compartments.
(3) A type 'A' ship, if over 150 m in length,
to which a freeboard less than type ’B’ has been assigned,
when loaded in accordance with the requirements of paragraph (11),
shall be able to withstand the flooding of any compartment or compartments,
with an assumed permeability of 0.95, consequent upon the damage assumptions
specified in paragraph (12), and shall remain afloat in a satisfactory
condition of equilibrium, as specified in paragraph (13). In such
a ship, the machinery space shall be treated as a floodable compartment,
but with a permeability of 0.85.
(4) A type 'A' ship shall be assigned a freeboard
not less than that based on table 28.1.
Type 'B' ships
(5) All ships which do not come within the provisions
regarding type 'A' ships in paragraphs (2) and (3) shall be considered
as type 'B' ships.
(6) Type 'B' ships, which in position 1 have hatch
covers which are permitted by the Administration to comply with the
requirements of regulation 15 (other than
paragraph (6)) or which are fitted with securing arrangements accepted
under the provisions of regulation 16(6),
shall be assigned freeboards based upon the values given in table 28.2, increased by the values given
in table 27.1:
Table 27.1 Freeboard increase
over tabular freeboard for type ’B’ ships, for ships with hatch covers complying
with the provisions of regulation 15 (other than paragraph (6))
Length of ship
(m)
|
Freeboard increase
(mm)
|
Length of ship
(m)
|
Freeboard increase
(mm)
|
Length of ship
(m)
|
Freeboard increase
(mm)
|
108 and
below
|
50
|
139
|
175
|
170
|
290
|
109
|
52
|
140
|
181
|
171
|
292
|
110
|
55
|
141
|
186
|
172
|
294
|
111
|
57
|
142
|
191
|
173
|
297
|
112
|
59
|
143
|
196
|
174
|
299
|
113
|
62
|
144
|
201
|
175
|
301
|
114
|
64
|
145
|
206
|
176
|
304
|
115
|
68
|
146
|
210
|
177
|
306
|
116
|
70
|
147
|
215
|
178
|
308
|
117
|
73
|
148
|
219
|
179
|
311
|
118
|
76
|
149
|
224
|
180
|
313
|
119
|
80
|
150
|
228
|
181
|
315
|
120
|
84
|
151
|
232
|
182
|
318
|
121
|
87
|
152
|
236
|
183
|
320
|
122
|
91
|
153
|
240
|
184
|
322
|
123
|
95
|
154
|
244
|
185
|
325
|
124
|
99
|
155
|
247
|
186
|
327
|
125
|
103
|
156
|
251
|
187
|
329
|
126
|
108
|
157
|
254
|
188
|
332
|
127
|
112
|
158
|
258
|
189
|
334
|
128
|
116
|
159
|
261
|
190
|
336
|
129
|
121
|
160
|
264
|
191
|
339
|
130
|
126
|
161
|
267
|
192
|
341
|
131
|
131
|
162
|
270
|
193
|
343
|
132
|
136
|
163
|
273
|
194
|
346
|
133
|
142
|
164
|
275
|
195
|
348
|
134
|
147
|
165
|
278
|
196
|
350
|
135
|
153
|
166
|
280
|
197
|
353
|
136
|
159
|
167
|
283
|
198
|
355
|
137
|
164
|
168
|
285
|
199
|
357
|
138
|
170
|
169
|
287
|
200
|
358
|
Freeboards at intermediate lengths of ship shall be obtained by linear
interpolation.
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Ships
above 200 m in length shall be dealt with by the Administration.
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(7) Type 'B' ships, which in position 1 have hatchways
fitted with hatch covers complying with the requirements of regulation 16(2) through (5), shall, except
as provided in paragraphs (8) to (13) inclusive, be assigned freeboards
based on table 28.2.
(8) Any type 'B' ship of over 100 m in length
may be assigned freeboards less than those required under paragraph
(7), provided that, in relation to the amount of reduction granted,
the Administration is satisfied that:
-
(a) the measures provided for the protection of
the crew are adequate;
-
(b) the freeing arrangements are adequate;
-
(c) the covers in position 1 and 2 comply with
the provisions of regulation 16(1) through (5)
and (7); and
-
(d) the ship, when loaded in accordance with the
requirements of paragraph (11), shall be able to withstand the flooding
of any compartment or compartments, with an assumed permeability of
0.95, consequent upon the damage assumptions specified in paragraph
(12), and shall remain afloat in a satisfactory condition of equilibrium,
as specified in paragraph (13). In such a ship, if over 150 m in length,
the machinery space shall be treated as a floodable compartment, but
with a permeability of 0.85.
(9) In calculating the freeboards for
type ’B’ ships which comply with the requirements of paragraphs
(8), (11), (12) and (13), the values from table
28.2 shall not be reduced by more than 60% of the difference
between the tabular values in tables 28.1 and 28.2 for the appropriate ship lengths.
(10)
-
(a) The reduction in tabular freeboard allowed
under paragraph (9) may be increased up to the total difference between
the values in table 28.1 and those in table 28.2 on condition that
the ship complies with the requirements of:
-
(i)
regulation 26,
other than paragraph (5), as if it were a type 'A' ship;
-
(ii) paragraphs (8), (11) and (13); and
-
(iii) paragraph (12), provided that throughout
the length of the ship any one transverse bulkhead will be assumed
to be damaged, such that two adjacent fore and aft compartments shall
be flooded simultaneously, except that such damage will not apply
to the boundary bulkheads of a machinery space.
-
(b) In such a ship, if over 150 m in length, the
machinery space shall be treated as a floodable compartment, but with
a permeability of 0.85.
Initial condition of loading
(11) The initial condition of loading before flooding
shall be determined as follows:
-
(a) The ship is loaded to its summer load waterline
on an imaginary even keel.
-
(b) When calculating the vertical centre of gravity,
the following principles apply:
-
(i) homogeneous cargo is carried;
-
(ii) all cargo compartments, except those referred
to under subparagraph (iii), but including compartments intended to
be partially filled, shall be considered fully loaded except that
in the case of fluid cargoes each compartment shall be treated as
98% full;
-
(iii) if the ship is intended to operate at its
summer load waterline with empty compartments, such compartments shall
be considered empty, provided the height of the centre of gravity
so calculated is not less than as calculated under subparagraph (ii);
-
(iv) 50 per cent of the ship's total capacity
of tanks and spaces fitted to contain each type of consumables and
stores is allowed for. It shall be assumed that for each type of liquid
at least one transverse pair or a single centreline tank has maximum
free surface, and the tank or combination of tanks to be taken into
account shall be those where the effect of free surfaces is the greatest;
in each tank the centre of gravity of the contents shall be taken
at the centre of volume of the tank. The remaining tanks shall be
assumed either completely empty or completely filled, and the distribution
of consumable liquids between these tanks shall be effected so as
to obtain the greatest possible height above the keel for the centre
of gravity;
-
(v) Ballast water tanks shall normally be considered
to be empty and no free surface correction shall be made for them.
-
(vi) Alternative treatment for free surface may
be considered when developing the final condition for application
of damage specified in regulation 27(12):
-
(aa) Method 1 (appropriate to virtual corrections).
The virtual centre of gravity for the initial condition is determined
as follows:
-
I the loading condition shall be developed in
accordance with paragraphs (i) to (iv);
-
ii the correction for the free surfaces is added
to the vertical centre of gravity;
-
iii one virtual initial condition with all compartments
empty is generated on summer load line draught with level trim, using
the vertical centre of gravity from the above loading condition; and
-
iv the damage cases will be checked for compliance
with the damage stability criteria using the above initial condition.
-
(bb) Method 2 (appropriate to the use of actual
free surface moments according to the assumed tank fillings for damage
case). The virtual centre of gravity for the initial condition is
determined as follows:
-
i the loading condition shall be developed in
accordance with paragraphs (i) to (iv);
-
ii one virtual initial condition for each damage
case with liquid-filled compartments may be generated on summer load
line draught with level trim, using the initial virtual condition
with filled compartments generated on summer load line draught with
level trim. Using the vertical centre of gravity and free surface
correction from the above loading condition separate calculations
for each damage case are performed, only the liquid-filled compartments
to be damaged are left empty before damage; and
-
iii the damage cases will be checked for compliance
with the damage stability criteria using above initial conditions
(one initial condition for each damage case)."
-
(vii) weights shall be calculated on the basis
of the following values for specific gravities:
|
salt water
|
1.025
|
|
fresh water
|
1.000
|
|
oil fuel
|
0.950
|
|
diesel oil
|
0.900
|
|
lubricating oil
|
0.900.
|
Damage assumptions
(12) The following principles regarding the character
of the assumed damage apply:
-
(a) The vertical extent of damage in all cases
is assumed to be from the base line upwards without limit.
-
(b) The transverse extent of damage is equal to
B/5 or 11.5 m, whichever is the lesser, measured inboard from the
side of the ship perpendicularly to the centreline at the level of
the summer load waterline.
-
(c) If damage of a lesser extent than specified
in subparagraphs (a) and (b) results in a more severe condition, such
lesser extent shall be assumed.
-
(d) Except where otherwise required by paragraph
(10)(a), the flooding shall be confined to a single compartment between
adjacent transverse bulkheads, provided that the inner longitudinal
boundary of the compartment is not in a position within the transverse
extent of assumed damage. Transverse boundary bulkheads of wing tanks,
which do not extend over the full breadth of the ship shall be assumed
not to be damaged, provided that they extend beyond the transverse
extent of assumed damage prescribed in subparagraph (b).
-
If in a transverse bulkhead there are steps or recesses
of not more than 3 m in length, located within the transverse extent
of assumed damage as defined in subparagraph (b), such transverse
bulkhead may be considered intact and the adjacent compartment may
be floodable singly. If, however, within the transverse extent of
assumed damage there is a step or recess of more than 3 m in length
in a transverse bulkhead, the two compartments adjacent to this bulkhead
shall be considered as flooded. The step formed by the afterpeak bulkhead
and the afterpeak tank top shall not be regarded as a step for the
purpose of this regulation.
-
(e) Where a main transverse bulkhead is located
within the transverse extent of assumed damage and is stepped in way
of a double bottom or side tank by more than 3 m, the double bottom
or side tanks adjacent to the stepped portion of the main transverse
bulkhead shall be considered as flooded simultaneously. If this side
tank has openings into one or several holds, such as grain feeding
holes, such hold or holds shall be considered as flooded simultaneously.
Similarly, in a ship designed for the carriage of fluid cargoes, if
a side tank has openings into adjacent compartments, such adjacent
compartments shall be considered as empty and as being flooded simultaneously.
This provision is applicable even where such openings are fitted with
closing appliances, except in the case of sluice valves fitted in
bulkheads between tanks and where the valves are controlled from the
deck. Manhole covers with closely spaced bolts are considered equivalent
to the unpierced bulkhead, except in the case of openings in topside
tanks making the topside tanks common to the holds.
-
(f) Where the flooding of any two adjacent fore
and aft compartments is envisaged, main transverse watertight bulkheads
shall be spaced at least 1/3 L2/3 or 14.5 m, whichever
is the lesser, in order to be considered effective. Where transverse
bulkheads are spaced at a lesser distance, one or more of these bulkheads
shall be assumed as non-existent in order to achieve the minimum spacing
between bulkheads.
Condition of equilibrium
(13) The condition of equilibrium after flooding
shall be regarded as satisfactory provided:
-
(a) The final waterline after flooding, taking
into account sinkage, heel and trim, is below the lower edge of any
opening through which progressive downflooding may take place. Such
openings shall include air pipes, ventilators (even if they comply
with regulation 19(4)) and openings which
are closed by means of weathertight doors (even if they comply with regulation 12) or hatch covers (even if they
comply with regulation 16(1) through (5)),
and may exclude those openings closed by means of manhole covers and
flush scuttles (which comply with regulation
18), cargo hatch covers of the type described in regulation 27(2), remotely operated sliding
watertight doors, and sidescuttles of the non-opening type (which
comply with regulation 23). However, in
the case of doors separating a main machinery space from a steering
gear compartment, watertight doors may be of a hinged, quick-acting
type kept closed at sea whilst not in use, provided also that the
lower sill of such doors is above the summer load waterline.
-
(b) If pipes, ducts or tunnels are situated within
the assumed extent of damage penetration as defined in paragraph (12)(b),
arrangements shall be made so that progressive flooding cannot thereby
extend to compartments other than those assumed to be floodable in
the calculation for each case of damage.
-
(c) The angle of heel due to unsymmetrical flooding
does not exceed 15°. If no part of the deck is immersed, an angle
of heel of up to 17° may be accepted.
-
(d) The metacentric height in the flooded condition
is positive.
-
(e) When any part of the deck outside the compartment
assumed flooded in a particular case of damage is immersed, or in
any case where the margin of stability in the flooded condition may
be considered doubtful, the residual stability is to be investigated.
It may be regarded as sufficient if the righting lever curve has a
minimum range of 20° beyond the position of equilibrium with a
maximum righting lever of at least 0.1 m within this range. The area
under the righting lever curve within this range shall be not less
than 0.0175 m.rad. The Administration shall give consideration to
the potential hazard presented by protected or unprotected openings
which may become temporarily immersed within the range of residual
stability.
-
(f) The Administration is satisfied that the stability
is sufficient during intermediate stages of flooding.
-
(g) Compliance with the residual stability criteria
specified in paragraphs (a), (c), (d) and (e) above is not required
to be demonstrated in service loading conditions using a stability
instrument, stability software or other approved method.
Ships without means of propulsion
(14) A lighter, barge or other ship without independent
means of propulsion shall be assigned a freeboard in accordance with
the provisions of these regulations. Barges which meet the requirements
of paragraphs (2) and (3) may be assigned type 'A' freeboards:
-
(a) The Administration should especially consider
the stability of barges with cargo on the weather deck. Deck cargo
can only be carried on barges to which the ordinary type 'B' freeboard
is assigned.
-
(b) However, in the case of barges which are unmanned,
the requirements of regulations 25, 26(3), 26(4) and 39 shall
not apply.
-
(c) Such unmanned barges which have on the freeboard
deck only small access openings closed by watertight gasketed covers
of steel or equivalent material may be assigned a freeboard 25% less
than those calculated in accordance with these regulations.
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