Feature 3
size and sea state, parameters which are not the worst possible combination of wave used as the basis for guidance. For a vessel
incorporated into conventional methods period and heading, so there are few full with full stability data, it is quite simple
of assessment, and it proved impossible to scale casualties for correlation purposes, to determine the maximum load, or the
compare monohull and multihull safety in but those that were found, mostly fishing maximum lift on a particular towing block
general, simply on the basis of the HSC Code vessels, appear to validate the method. It or derrick, at which the residual stability is
criteria. Although hypothetical craft could has therefore been presented to the IMO reduced to some particular level. Two levels
be compared directly, actual multihulls tend for consideration, but it is expected that were proposed; amber, at which the vessel
to be much safer than monohulls because further validation for a range of vessel types may be described as having a low level of
they tend to have greater margins of stability may be required before it can be given full safety, and red, at which there is danger
over the minimum criteria. consideration in that forum, and the MCA of capsize. In each case, the situation is
The findings were interesting, and has invited tenders for Research Project 583, associated with a maximum recommended
demonstrated that conventional criteria which will address that. sea state. The amber level was aligned with
are not the best measures of safety. It is the The conventional system of stability the safety offered by the minimum criteria,
residual stability in the presence of moments assessment discourages fishermen from and the red level at 50% of that in terms of
such as passenger crowding or wind heeling considering their stability, because they go the maximum sea state. The guidance cannot
that governs the safety, but it is the upright to sea confident in the knowledge that it be precise, but is intended to raise the safety
stability that is assessed most rigorously. complies with the relevant requirements awareness of the crew, assisting them in
Vulnerability did not appear to be influenced in all operating conditions. Inadequacies of their decisions on loading and lifting, having
by the form of the vessel, number of hulls, the conventional system are that it does not regard to the prevailing conditions.
or the existence or extent of damage. All necessarily address the effects of operational For the smaller vessels, the source
Intact Monohulls
configurations may be considered as floating loads or moments, does not address safety of guidance information was more
Damaged Monohulls
bodies characterised by their residual in terms of the size of the vessel in relation problematic, because the expense of a full
Intact Catamarans
stability curve. The vulnerability to capsize to the sea state, does not provide practical stability assessment would not be acceptable
Damaged Catamarans
is most dependent on the range of positive guidance on varying levels of safety, and politically. The research involved a study
Damaged Trimaran
residual stability and, to a lesser extent, the does not present information in a simple of fleet characteristics, and the stability of
ma
A
x
0.
i
12
mum residual righting moment. format. Regulatory boundaries have driven sample vessels, together with calculations
/
L
O
A
0
.10
new method was proposed to assess designs in undesirable ways and this was on systematic variations of hullform and
the level of safety on the basis of these something to be avoided in this work. loading. The proposed method is for the
a
p
s
i
z
e
cha
0
r
.
a
08
cteristics and the size of the vessel The recommendation was for a Stability same information to be provided as for the
rel
t
t
o
C
a
0
t
.
i
06
ve to the operational sea state. The Notice; a single page of information posted larger vessels, but basing the guidance on the
sine
i
g
h
gle formula developed may be applied to prominently on the vessel, simple enough to residual freeboard. Heavily loaded vessels,
all
H
t
0
y
.04
pes of hullform, intact or damaged. It be understood and memorised by the crew. or those lifting heavy weights over the side,
a
v
e
follows, therefore, that it may be applied to It is proposed to provide information that are far more vulnerable to capsize, and this
.
W
0.02
alli
n
types of ship. stability is variable, may be inadequate, and is reflected on the Stability Notice, Figure
M
I0n. 00some cases, the waves in which it was is under the control of the fishermen. 4. An additional recommendation was for
0.0 0.2 0.4 0.6 0.8 1.0 1.2
possible to cap
R
s
a
iz
n
e
g
e
t
(
h
R
e
M
m
m
ax
o
)
d
^0.
el
5
s were lower The method developed in Project 509, a freeboard guidance mark to be placed
than the operationalLB limits of the ferries to relate residual stability to safety with on the vessel’s side, indicating the residual
Figure
on wh
3.
ic
The
h t
strong
he mo
relatio
dels
n
w
shi
e
p
re
betwee
based
n
.
minimu
The t
m
es
wave
ts
height
regard
to
t
cap
o v
s
e
iz
s
e,
se
and
l siz
a
e
prop
and
osed
sea
st
s
ability
tate, was ideal freeboards corresponding to the safety zone
parameter.
represented the dead ship condition, and for application to fishing vessels, and was boundaries. These would have no regulatory
purpose, but would enable the crew to
STABILITY NOTICE
relate the stability notice directly to the
Name: Jolly Polly SAFETY GUIDANCE
No: AB789
vessel operation. They would also indicate
LOA: 10.6m
LOADING &
Maximum
the relative safety of different vessels, and
Beam: 3.85m
HAULER USE
Zone
Minimum
Freeboard
recommended
seastate perhaps increase the safety awareness of a
Owner: John Potter
fishing community. The information for the
Good margin of residual
notice can be derived in a few minutes with
freeboard
Good margin At least
of safety 47cm a calculator, using only the length and beam
of the vessel to determine the guidance
freeboards and sea states, and might be a
Loading or hauling reduces
minimum freeboard to less Low level of valuable tool with which to improve the very
than 47cm safety
24 to 47 cm 1.3 metres
low safety levels that occur in some parts of
the world. NA
Excessive loading or hauling
reduces minimum freeboard to Danger of Less than
less than 24cm capsize 24cm
0.6 metres
Figure 4. example Stability Notice for a
small fishing boat with no stability data.
Figure 4. Example Stability Notice for a small fishing boat with no stability data.
The Naval Architect January 2008 61
NA Jan - p59+60+
61.indd 61 04/01/2008 15:52:09
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