5.1
The comparison of the
different assessments of the weather criterion using experimental
results is summarized in table 5.1. In the table all the possible
combinations of the wind tests and the drifting tests for estimating lw1
are included (see paragraph 1.5 of the Guidelines).
As for φ
1, the standard criterion (paragraph
3.2.2.3 of the Code) and the result of the direct measurement procedure
are included. The results of the three steps procedure can be omitted
here since the estimated φ
1 was almost
equal to the one of direct measurement procedure for this ship. The
PIT estimation is reported in section 6 below. The last line of table
5.1 shows the critical values of KGs, in which b/a=1. These last results
are to be taken with some caution, since the effects of changing the
vertical centre of gravity on Tr
and on the
other quantities related to roll motion including φ
1 have been neglected. A considerable extension of the experimental
tests would have been indeed required to correctly evaluate the limiting
KG curve.
Assessment of weather
criterion
| lw1
|
Standard Weather Criterion
|
Wind test
+
Drift test
|
Wind test
+
draft/2
|
Wind test
(upright)
+
Drift test
|
Wind test
(upright)
+
draft/2
|
Standard Weather Criterion
|
Wind test
+
Drift test
|
Wind test
+
draft/2
|
Wind test
(upright)
+
Drift test
|
Wind test
(upright)
+
draft/2
|
|
Φ1
|
Standard
Weather Criterion
|
Direct
Procedure (or Three Steps Procedure)
|
| lw1 [m]
|
0.153
|
Function
of heel angle
|
0.125
|
0.153
|
Function of heel angle
|
0.125
|
| r [-]
|
1.096
|
0.759
(Three Steps Procedure)
|
| Tr [sec]
|
16.3
|
17.9
|
| s [-]
|
0.0431
|
0.0383
|
|
Φ1 [deg]
|
15.4
|
19.3
|
|
Φ0 [deg]
|
6.1
|
3.7
|
4.9
|
3.8
|
5.0
|
6.1
|
3.7
|
4.9
|
3.8
|
5.0
|
|
Φ0 – Φ1 [deg]
|
–9.3
|
–11.7
|
–10.4
|
–11.6
|
–10.4
|
–13.2
|
–15.7
|
–14.4
|
–15.5
|
–14.3
|
|
Φf [deg]
|
39.5
|
| Area a [rad-m]
|
0.075
|
0.063
|
0.069
|
0.063
|
0.070
|
0.111
|
0.096
|
0.103
|
0.095
|
0.106
|
| Area b[rad-m]
|
0.224
|
0.295
|
0.259
|
0.276
|
0.247
|
0.224
|
0.295
|
0.259
|
0.276
|
0.247
|
| b/a [-]
|
2.99
|
4.71
|
3.76
|
4.41
|
3.51
|
2.02
|
3.09
|
2.51
|
2.90
|
2.34
|
| Crit KG [m]
|
11.48
|
11.88
|
11.68
|
11.79
|
11.62
|
11.35
|
11.82
|
11.59
|
11.73
|
11.52
|
5.2
Table 5.1 shows that the alternative
assessment by model experiment can change the ratio of areas, b/a,
significantly with respect to the standard criterion, whereas the
changes in the limiting value of the vertical centre of gravity are
more contained. For this ship, the increased φ
1 obtained
by experiments makes b/a smaller, and the lw1
evaluated
through all the combinations of the wind tests and drifting tests,
complete procedures and simplified procedures, tends to make b/a larger
than the standard weather criterion as contained in paragraph 3.2
of the Code. It has to be noted, however, that the fluctuations are
related to the large variation in the vertical centre of hydrodynamic
pressure in drift motion of this ship. More extensive confirmation
are awaited from the experience gained through the application of
the Interim Guidelines.