3.1 The material of which the model is made is
not important in itself, provided that the model, both in the intact
and damaged condition, is sufficiently rigid to ensure that its hydrostatic
properties are the same as those of the actual ship and also that
the flexural response of the hull in waves is negligible.
It is also important to ensure that the damaged compartments
are modelled as accurately as practicably possible to ensure that
the correct volume of floodwater is represented.
Since
ingress of water (even small amounts) into the intact parts of the
model will affect its behaviour, measures must be taken so that this
ingress does not occur.
In model tests involving worst
SOLAS damages near the ship ends, it was observed that progressive
flooding was not possible because of the tendency of the water on
deck to accumulate near the damage opening and hence flow out. As
such models were able to survive very high sea states, while they
capsized in lesser sea states with less onerous SOLAS damages, away
from the ends, the limit ±35% was introduced to prevent this.
Extensive research carried out for the purpose of developing
appropriate criteria for new vessels has clearly shown that in addition
to the GM and freeboard being important parameters in the survivability
of passenger ships, the area under the residual stability curve is
also another major factor. Consequently in choosing the worst SOLAS
damage for compliance with the requirement of paragraph 3.5.1 the
worst damage is to be taken as that which gives the least area under
the residual stability curve.
3.2 Model particulars
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.1 It has been found during tests that the vertical
extent of the model can affect the results when tested dynamically.
It is therefore required that the ship be modelled to at least three
superstructure standard heights above the bulkhead (freeboard) deck
so that the large waves of the wave train do not break over the model.
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.2 The model in way of the assumed damages should
be as thin as practically possible to ensure that the amount of floodwater
and its centre of gravity are adequately represented. The hull thickness
should not exceed 4 mm. It is recognised that it may not be possible
for the model hull and the elements of primary and secondary subdivision
in way of the damage to be constructed with sufficient detail and
due to these constructional limitations it may not be possible to
calculate accurately the assumed permeability of the space.
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.3 It is important that not only the draughts
in the intact condition are verified but also that the draughts of
the damaged model are accurately measured for correlation with those
derived from the damaged stability calculation. For practical reasons
a tolerance of +2 mm in any draught is accepted.
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.4 After measuring the damaged draughts it may
be found necessary to make adjustments to the permeability of the
damaged compartment by either introducing intact volumes or by adding
weights. However, it is also important to ensure that the centre of
gravity of the floodwater is accurately represented. In this case
any adjustments made must err on the side of safety.
If the model is required to be fitted with barriers on deck
and their height is less than the bulkhead height indicated below,
the model should be fitted with CCTV so that any "splashing over"
and any accumulation of water on the undamaged area of the deck can
be monitored. In this case a video recording of the event should form
part of the tests records.
The height of transverse or longitudinal bulkheads which are
taken into account as effective to confine the assumed accumulated
sea water in the compartment concerned in the damaged ro-ro deck should
be at least 4 m in height unless the height of water is less than
0.5 m. In such cases the height of the bulkhead may be calculated
in accordance with the following:
Bh = 8hw
Bh is the bulkhead height; and
hw is the height of water.
In any event, the minimum height of the bulkhead should be not
less than 2.2 m. However, in the case of a ship with hanging car decks,
the minimum height of the bulkhead should be not less than the height
to the underside of the hanging car deck when in its lowered position.
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.5 In order to ensure that the model motion characteristics
represent those of the actual ship it is important that the model
is inclined in the intact condition so that the intact GM is verified.
The mass distribution should be measured in air. The transverse radius
of gyration of the actual ship should be in the range 0.35B to 0.4B
and the longitudinal radius of gyration should be in the range 0.2L
to 0.25L.
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.6 It is assumed that the ventilators of the damaged
compartment of the actual ship are adequate for unhindered flooding
and movement of the floodwater. However in trying to scale down the
ventilating arrangements of the actual ship undesirable scale effects
may be introduced. In order to ensure that these do not occur it is
recommended to construct the ventilating arrangements to a larger
scale than that of the model, ensuring that this does not affect the
flow of water on the car deck.
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.7 It is deemed appropriate to consider a damage
shape representative of a cross section of the striking ship in the
bow region. The 15° angle is based on a study of the cross section
at a distance of B/5 from the bow for a representative selection of
vessels of different types and sizes.
The isosceles triangular profile of the prismatic damage shape
is that corresponding to the load waterline.
Additionally, in cases where side casings of width less than
B/5 are fitted and in order to avoid any possible scale effects, the
damage length in way of the side casings should not be less than 25
mm.
3.3 In the original model test method of resolution
14 of the 1995 SOLAS Conference the effect of heeling induced by the
maximum moment deriving from any of passenger crowding, launching
of survival craft, wind and turning was not considered even though
this effect was part of SOLAS. Results from an investigation have
shown however that it would be prudent to take these effects into
account and to retain the minimum of 1° heel towards the damage
for practical purposes. It is to be noted that heeling due to turning
was considered not to be relevant.
3.4 In cases where there is a margin in GM in
the actual loading conditions compared to the GM limiting curve (derived
from SOLAS 90), the Administration may accept that this margin is
taken advantage of in the model test. In such cases the GM limiting
curve should be adjusted. This adjustment can be done as follows:
Figure 1 GM limiting curve adjustment
d = dS — 0.6 ( dS - dLS )
where: dS is the subdivision draught; and
dLS is the lightship draught.
The adjusted curve is a straight line between the GM used
in the model test at the subdivision draught and the intersection
of the original SOLAS 90 curve and draught d.