1.1.1 The stability shall be sufficient to satisfy
the provisions of 2.3, 2.4 and 2.6 of
this Code.
1.1.2
Heeling moment due to turning
The heeling moment developed during manoeuvring of the craft
in the displacement mode may be derived from the following formula:
where:
|
M
R
|
= |
moment of heeling; |
|
V
o
|
= |
speed of the craft in the turn (m/s); |
|
Δ |
= |
displacement
(t); |
|
L
|
= |
length
of the craft on the waterline (m); |
|
KG
|
= |
height
of the centre of gravity above keel (m). |
This formula is applicable when the ratio of the radius of the
turning circle to the length of the craft is 2 to 4.
1.1.3
Relationship between the capsizing
moment and heeling moment to satisfy the weather criterion
The stability of a hydrofoil boat in the displacement mode can
be checked for compliance with the weather criterion K as
follows:
where:
|
M
c
|
= |
minimum capsizing moment as determined when account is taken
of rolling; |
|
M
v
|
= |
dynamically applied heeling moment due to the wind pressure. |
1.1.4
Heeling moment due to wind pressure
The heeling moment MV
shall be taken
as constant during the whole range of heel angles and calculated by
the following expression:
where:
|
P
V
|
= |
wind pressure = 750 (V
W/ 26)2 (N/m2)
|
|
A
V
|
= |
windage area including the projections of the lateral surfaces
of the hull, superstructure and various structures above the waterline
(m2)
|
|
Z
|
= |
windage
area lever (m) = the vertical distance to the geometrical centre of
the windage area from the waterline |
|
V
W
|
= |
the wind speed corresponding to the worst intended conditions
(m/s). |
1.1.5
Evaluation of the minimum
capsizing moment Mc in the displacement mode
The minimum capsizing moment is determined from the static and
dynamic stability curves taking rolling into account.
-
.1 When the static stability curve is used, Mc is
determined by equating the areas under the curves of the capsizing
and righting moments (or levers) taking rolling into account, as indicated
by figure 1, where θ
z is the amplitude of roll and MK is a line drawn parallel to
the abscissa axis such that the shaded areas S1 and S2 are
equal.
|
M
c
|
= |
OM, if the scale of ordinates represents moments, |
|
M
c
|
= |
OM x displacement, if the scale of ordinates represents
levers.
|
-
.2 When the dynamic stability curve is used, first
an auxiliary point A shall be determined. For this purpose the amplitude
of heeling is plotted to the right along the abscissa axis and a point
A' is found (see figure 2 ).
A line AA' is drawn parallel to the abscissa axis equal to the double
amplitude of heeling (AA' = 2θ
z) and
the required auxiliary point A is found. A tangent AC to the dynamic
stability curve is drawn. From the point A the line AB is drawn parallel
to the abscissa axis and equal to 1 radian (57.3°). From the point
B a perpendicular is drawn to intersect with the tangent in point
E. The distance 
is equal to the capsizing moment if measured along the
ordinate axis of the dynamic stability curve. If, however, the dynamic
stability levers are plotted along this axis, 
is then the capsizing lever, and in this case the capsizing
moment M
c is determined by multiplication
of ordinate 
(in metres) by the corresponding displacement in tonnes
M
c = 9.81 Δ
(kNm)
-
.3 The amplitude of rolling θ
z is determined by means of model and full-scale tests in irregular
seas as a maximum amplitude of rolling of 50 oscillations of a craft
travelling at 90° to the wave direction in sea state for the worst
design condition. If such data are lacking the amplitude is assumed
to be equal to 15°.
-
.4 The effectiveness of the stability curves shall be limited to
the angle of flooding.
Figure 1 Static Stability Curve
Figure 2 Dynamic Stability Curve